swt.informatik.uni-freiburg.de · – 2014-04 – main – F o r m a l M e t hod s f o r C S e m i...
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– 2014-04 – main – Formal Methods for C Seminar – Summer Semester 2014 Daniel Dietsch, Sergio Feo Arenis, Marius Greitschus, Bernd Westphal Content – 2014-04 – overview – 7/125 • Brief history • Comments • Declarations and Scopes • Variables • Expressions and Statements • Functions • Scopes • Pointers • Dynamic Storage & Storage Duration • Storage Class Specifiers • Strings and I/O • Tools & Modules • Formal Methods for C • Common Errors Function Pointers – 2014-04 – pointers – 36/125 Functions in the System’s Memory – 2014-04 – pointers – 37/125 1 void f() { return ; } ... 0x1000 0x1001 RET 0x1002 0x1003 0x1004 0x1005 0x1006 0x1007 0x1008 0x1009 0x100A 0x100B 0x100C 0x100D 0x100E 0x100F 0x1010 0x1011 0x1012 0x1013 0x1014 0x1015 0x1016 0x1017 ... the compiler chose to store the machine code of ’f’ at memory cell with address 0x1001 Calling Functions – 2014-04 – pointers – 38/125 1 void f() { return ; } 2 f(); Calling Functions – 2014-04 – pointers – 38/125 1 void f() { return ; } 2 f(); ... 0x1000 0x1001 RET 0x1002 0x1003 0x1004 0x1005 0x1006 0x1007 0x1008 0x1009 0x100A 0x100B CALL 0x100C 0x10 0x100D 0x01 0x100E 0x100F 0x1010 0x1011 0x1012 0x1013 0x1014 0x1015 0x1016 0x1017 ... calling ’f’ means machine op CALL with address of callee (here: f, address 0x1001)
Transcript of swt.informatik.uni-freiburg.de · – 2014-04 – main – F o r m a l M e t hod s f o r C S e m i...
– 2014-04 – main –
Form
al
Meth
ods
for
C
Sem
ina
r–
Su
mm
erS
emester
20
14
Daniel
Dietsch
,Serg
ioFeo
Aren
is,Mariu
sGreitsch
us,BerndW
estp
hal
Conten
t
– 2014-04 – overview –
7/125
•Brief
history
•Comments
•Declaratio
nsandScopes
•Variab
les
•Expression
sandStatem
ents
•Function
s
•Scop
es
•Pointers
•Dynam
icStorag
e&
Storag
eDuratio
n
•Storag
eClass
Specifi
ers
•Strin
gsandI/O
•Tools&
Modules
•Form
alMeth
odsfor
C
•CommonErrors
Fu
nctio
nP
oin
ters
– 2014-04 – pointers –
36/125
Functio
ns
inth
eSystem
’sM
emory
– 2014-04 – pointers –
37/125
1void
f()
{retu
rn;
}
...0x1000
0x1001
RET
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
thecompiler
chose
tostore
themach
inecode
of’f’
atmem
orycell
with
address
0x1001
Callin
gF
unctio
ns
– 2014-04 – pointers –
38/125
1void
f()
{retu
rn;
}2
f();
Callin
gF
unctio
ns
– 2014-04 – pointers –
38/125
1void
f()
{retu
rn;
}2
f();
...0x1000
0x1001
RET
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
CALL
0x100C
0x10
0x100D
0x01
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
calling’f’
mean
smach
ineopCALLwith
address
ofcallee
(here:
f,address
0x1001)
AP
oin
terto
‘f’
(16-b
itA
rchitectu
re)
– 2014-04 – pointers –
39/125
1void
f()
{retu
rn;
}2
f();
3void
(∗p)
()
=&f;
AP
oin
terto
‘f’
(16-b
itA
rchitectu
re)
– 2014-04 – pointers –
39/125
1void
f()
{retu
rn;
}2
f();
3void
(∗p)
()
=&f;
...0x1000
0x1001
RET
0x1002
0x1003
0x1004
0x10
0x1005
0x01
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
CALL
0x100C
0x10
0x100D
0x01
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
‘p’isavariab
lewhich
storestheaddress
ofa
functio
n(here:
of‘f’)
Dereferen
ceF
unctio
nP
oin
ters
– 2014-04 – pointers –
40/125
1void
f()
{retu
rn;
}2
f();
3void
(∗p)
()
=&f;
4(∗
p)();
...0x1000
0x1001
RET
0x1002
0x1003
0x1004
0x10
0x1005
0x01
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
CALL
0x100C
0x10
0x100D
0x01
0x100E
0x100F
0x1010
MOV
0x1011
0x10
0x1012
0x04
0x1013R
0x1014
CALL
0x1015R
0x1016
0x1017
...
Dereferen
ceF
unctio
nP
oin
ters
– 2014-04 – pointers –
40/125
1void
f()
{retu
rn;
}2
f();
3void
(∗p)
()
=&f;
4(∗
p)();
...0x1000
0x1001
RET
0x1002
0x1003
0x1004
0x10
0x1005
0x01
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
CALL
0x100C
0x10
0x100D
0x01
0x100E
0x100F
0x1010
MOV
0x1011
0x10
0x1012
0x04
0x1013R
0x1014
CALL
0x1015R
0x1016
0x1017
...
callingvia
‘p’mean
sread
valueofp(here:
0x1001)
into
register
R...
Dereferen
ceF
unctio
nP
oin
ters
– 2014-04 – pointers –
40/125
1void
f()
{retu
rn;
}2
f();
3void
(∗p)
()
=&f;
4(∗
p)();
...0x1000
0x1001
RET
0x1002
0x1003
0x1004
0x10
0x1005
0x01
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
CALL
0x100C
0x10
0x100D
0x01
0x100E
0x100F
0x1010
MOV
0x1011
0x10
0x1012
0x04
0x1013R
0x1014
CALL
0x1015R
0x1016
0x1017
...
callingvia
‘p’mean
sread
valueofp(here:
0x1001)
into
register
R...
...andthen
mach
ineop
CALLwith
R,calls
address
storedin
R
Po
inters
vs.A
rrays
– 2014-04 – pointers –
41/125
Arra
ys
– 2014-04 – pointers –
42/125
1char
a[5
]=
{’H
’,
’e’,
’l’,
’l’,
’o’
};
reservesom
espace
for5ch
ars...
...andlet
apoin
tto
that
space
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
’H’
0x1009
’e’0x100A’l’
0x100B’l’
0x100C
’o’
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
a
Arra
ys
– 2014-04 – pointers –
43/125
1char
a[5
]=
{’H
’,
’e’,
’l’,
’l’,
’o’
};
2int
i;
3fo
r(i=
0;
i<
5;++i)
4a[i]=
’x’;
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x..
0x1004
0x..
0x1005
0x1006
0x1007
0x1008
’H’
0x1009
’e’0x100A’l’
0x100B’l’
0x100C
’o’
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
i
Arra
ys
– 2014-04 – pointers –
43/125
1char
a[5
]=
{’H
’,
’e’,
’l’,
’l’,
’o’
};
2int
i;
3fo
r(i=
0;
i<
5;++i)
4a[i]=
’x’;
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x00
0x1004
0x01
0x1005
0x1006
0x1007
0x1008
’x’0x1009
’e’0x100A’l’
0x100B’l’
0x100C
’o’
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
i
Arra
ys
– 2014-04 – pointers –
43/125
1char
a[5
]=
{’H
’,
’e’,
’l’,
’l’,
’o’
};
2int
i;
3fo
r(i=
0;
i<
5;++i)
4a[i]=
’x’;
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x00
0x1004
0x02
0x1005
0x1006
0x1007
0x1008
’x’0x1009
’x’0x100A’l’
0x100B’l’
0x100C
’o’
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
i
Arra
ys
– 2014-04 – pointers –
43/125
1char
a[5
]=
{’H
’,
’e’,
’l’,
’l’,
’o’
};
2int
i;
3fo
r(i=
0;
i<
5;++i)
4a[i]=
’x’;
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x00
0x1004
0x03
0x1005
0x1006
0x1007
0x1008
’x’0x1009
’x’0x100A
’x’0x100B’l’
0x100C
’o’
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
i
Arra
ys
– 2014-04 – pointers –
43/125
1char
a[5
]=
{’H
’,
’e’,
’l’,
’l’,
’o’
};
2int
i;
3fo
r(i=
0;
i<
5;++i)
4a[i]=
’x’;
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x00
0x1004
0x04
0x1005
0x1006
0x1007
0x1008
’x’0x1009
’x’0x100A
’x’0x100B
’x’0x100C
’o’
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
i
Arra
ys
– 2014-04 – pointers –
43/125
1char
a[5
]=
{’H
’,
’e’,
’l’,
’l’,
’o’
};
2int
i;
3fo
r(i=
0;
i<
5;++i)
4a[i]=
’x’;
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x00
0x1004
0x05
0x1005
0x1006
0x1007
0x1008
’x’0x1009
’x’0x100A
’x’0x100B
’x’0x100C
’x’0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
i
Arra
ysvs.
Poin
ters
– 2014-04 – pointers –
44/125
1char
a[5
]=
{’H
’,
’e’,
’l’,
’l’,
’o’
};
2char∗
p=
a;
//
not&a
!3
for
(int
i=
0;
i<
5;++i,++p)
4∗p
=’o
’;
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x..
0x1004
0x..
0x1005
0x1006
0x1007
0x1008
’x’0x1009
’x’0x100A
’x’0x100B
’x’0x100C
’x’0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
p
Arra
ysvs.
Poin
ters
– 2014-04 – pointers –
44/125
1char
a[5
]=
{’H
’,
’e’,
’l’,
’l’,
’o’
};
2char∗
p=
a;
//
not&a
!3
for
(int
i=
0;
i<
5;++i,++p)
4∗p
=’o
’;
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x08
0x1005
0x1006
0x1007
0x1008
’x’0x1009
’x’0x100A
’x’0x100B
’x’0x100C
’x’0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
p
Arra
ysvs.
Poin
ters
– 2014-04 – pointers –
44/125
1char
a[5
]=
{’H
’,
’e’,
’l’,
’l’,
’o’
};
2char∗
p=
a;
//
not&a
!3
for
(int
i=
0;
i<
5;++i,++p)
4∗p
=’o
’;
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x09
0x1005
0x1006
0x1007
0x1008
’o’
0x1009
’x’0x100A
’x’0x100B
’x’0x100C
’x’0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
p
Arra
ysvs.
Poin
ters
– 2014-04 – pointers –
44/125
1char
a[5
]=
{’H
’,
’e’,
’l’,
’l’,
’o’
};
2char∗
p=
a;
//
not&a
!3
for
(int
i=
0;
i<
5;++i,++p)
4∗p
=’o
’;
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0A
0x1005
0x1006
0x1007
0x1008
’o’
0x1009
’o’
0x100A
’x’0x100B
’x’0x100C
’x’0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
p
Arra
ysvs.
Poin
ters
– 2014-04 – pointers –
44/125
1char
a[5
]=
{’H
’,
’e’,
’l’,
’l’,
’o’
};
2char∗
p=
a;
//
not&a
!3
for
(int
i=
0;
i<
5;++i,++p)
4∗p
=’o
’;
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0B
0x1005
0x1006
0x1007
0x1008
’o’
0x1009
’o’
0x100A
’o’
0x100B
’x’0x100C
’x’0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
p
Arra
ysvs.
Poin
ters
– 2014-04 – pointers –
44/125
1char
a[5
]=
{’H
’,
’e’,
’l’,
’l’,
’o’
};
2char∗
p=
a;
//
not&a
!3
for
(int
i=
0;
i<
5;++i,++p)
4∗p
=’o
’;
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0C
0x1005
0x1006
0x1007
0x1008
’o’
0x1009
’o’
0x100A
’o’
0x100B
’o’
0x100C
’x’0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
p
Arra
ysvs.
Poin
ters
– 2014-04 – pointers –
44/125
1char
a[5
]=
{’H
’,
’e’,
’l’,
’l’,
’o’
};
2char∗
p=
a;
//
not&a
!3
for
(int
i=
0;
i<
5;++i,++p)
4∗p
=’o
’;
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0D
0x1005
0x1006
0x1007
0x1008
’o’
0x1009
’o’
0x100A
’o’
0x100B
’o’
0x100C
’o’
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
p
Integ
erA
rrays
– 2014-04 – pointers –
45/125
1int
a[3
]=
{10,
010,
0x1234
};
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x00
0x1009
0x0A
0x100A
0x00
0x100B
0x08
0x100C
0x12
0x100D
0x34
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
a
reservesom
espace
for3ints...
...andlet
apoin
tto
that
space
Integ
erA
rrays
– 2014-04 – pointers –
46/125
1int
a[3
]=
{10,
010,
0x1234
};
2int
i;
3fo
r(i=
0;
i<
3;++i)
4a[i]=
0x27;...
0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x..
0x1004
0x..
0x1005
0x1006
0x1007
0x1008
0x00
0x1009
0x0A
0x100A
0x00
0x100B
0x08
0x100C
0x12
0x100D
0x34
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
i
Integ
erA
rrays
– 2014-04 – pointers –
46/125
1int
a[3
]=
{10,
010,
0x1234
};
2int
i;
3fo
r(i=
0;
i<
3;++i)
4a[i]=
0x27;...
0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x00
0x1004
0x01
0x1005
0x1006
0x1007
0x1008
0x00
0x1009
0x27
0x100A
0x00
0x100B
0x08
0x100C
0x12
0x100D
0x34
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
i
Integ
erA
rrays
– 2014-04 – pointers –
46/125
1int
a[3
]=
{10,
010,
0x1234
};
2int
i;
3fo
r(i=
0;
i<
3;++i)
4a[i]=
0x27;...
0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x00
0x1004
0x02
0x1005
0x1006
0x1007
0x1008
0x00
0x1009
0x27
0x100A
0x00
0x100B
0x27
0x100C
0x12
0x100D
0x34
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
i
Integ
erA
rrays
– 2014-04 – pointers –
46/125
1int
a[3
]=
{10,
010,
0x1234
};
2int
i;
3fo
r(i=
0;
i<
3;++i)
4a[i]=
0x27;...
0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x00
0x1004
0x03
0x1005
0x1006
0x1007
0x1008
0x00
0x1009
0x27
0x100A
0x00
0x100B
0x27
0x100C
0x00
0x100D
0x27
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
i
Integ
erA
rrays
vs.P
oin
ters
– 2014-04 – pointers –
47/125
1int
a[3
]=
{10,
010,
0x1234
};
2int∗
p=
a;
3fo
r(int
i=
0;
i<
3;++p)
4∗p
=0x3421;...
0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x..
0x1004
0x..
0x1005
0x1006
0x1007
0x1008
0x00
0x1009
0x27
0x100A
0x00
0x100B
0x27
0x100C
0x00
0x100D
0x27
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
p
Integ
erA
rrays
vs.P
oin
ters
– 2014-04 – pointers –
47/125
1int
a[3
]=
{10,
010,
0x1234
};
2int∗
p=
a;
3fo
r(int
i=
0;
i<
3;++p)
4∗p
=0x3421;...
0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x08
0x1005
0x1006
0x1007
0x1008
0x00
0x1009
0x27
0x100A
0x00
0x100B
0x27
0x100C
0x00
0x100D
0x27
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
p
Integ
erA
rrays
vs.P
oin
ters
– 2014-04 – pointers –
47/125
1int
a[3
]=
{10,
010,
0x1234
};
2int∗
p=
a;
3fo
r(int
i=
0;
i<
3;++p)
4∗p
=0x3421;...
0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0A
0x1005
0x1006
0x1007
0x1008
0x34
0x1009
0x21
0x100A
0x00
0x100B
0x27
0x100C
0x00
0x100D
0x27
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
p
Integ
erA
rrays
vs.P
oin
ters
– 2014-04 – pointers –
47/125
1int
a[3
]=
{10,
010,
0x1234
};
2int∗
p=
a;
3fo
r(int
i=
0;
i<
3;++p)
4∗p
=0x3421;...
0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0C
0x1005
0x1006
0x1007
0x1008
0x34
0x1009
0x21
0x100A
0x34
0x100B
0x21
0x100C
0x00
0x100D
0x27
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
p
Integ
erA
rrays
vs.P
oin
ters
– 2014-04 – pointers –
47/125
1int
a[3
]=
{10,
010,
0x1234
};
2int∗
p=
a;
3fo
r(int
i=
0;
i<
3;++p)
4∗p
=0x3421;...
0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0E
0x1005
0x1006
0x1007
0x1008
0x34
0x1009
0x21
0x100A
0x34
0x100B
0x21
0x100C
0x34
0x100D
0x21
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
p
Po
inters
to’vo
id’,
Po
inter
Arith
metic
– 2014-04 – pointers –
48/125
Poin
terto
’void
’
– 2014-04 – pointers –
49/125
1int[3
]a
={
10,
010,
0x1234
};
2int∗
p=
a;
3void
∗q
=a;
4fo
r(int
i=
0;
i<
3;++i)
{5
p++;
6q++;
7}
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x08
0x1005
0x10
0x1006
0x08
0x1007
0x1008
0x00
0x1009
0x0A
0x100A
0x00
0x100B
0x08
0x100C
0x12
0x100D
0x34
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
pq
Poin
terto
’void
’
– 2014-04 – pointers –
49/125
1int[3
]a
={
10,
010,
0x1234
};
2int∗
p=
a;
3void
∗q
=a;
4fo
r(int
i=
0;
i<
3;++i)
{5
p++;
6q++;
7}
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0A
0x1005
0x10
0x1006
0x08
0x1007
0x1008
0x00
0x1009
0x0A
0x100A
0x00
0x100B
0x08
0x100C
0x12
0x100D
0x34
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
pq
Poin
terto
’void
’
– 2014-04 – pointers –
49/125
1int[3
]a
={
10,
010,
0x1234
};
2int∗
p=
a;
3void
∗q
=a;
4fo
r(int
i=
0;
i<
3;++i)
{5
p++;
6q++;
7}
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0A
0x1005
0x10
0x1006
0x09
0x1007
0x1008
0x00
0x1009
0x0A
0x100A
0x00
0x100B
0x08
0x100C
0x12
0x100D
0x34
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
pq
Poin
terto
’void
’
– 2014-04 – pointers –
49/125
1int[3
]a
={
10,
010,
0x1234
};
2int∗
p=
a;
3void
∗q
=a;
4fo
r(int
i=
0;
i<
3;++i)
{5
p++;
6q++;
7}
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0C
0x1005
0x10
0x1006
0x09
0x1007
0x1008
0x00
0x1009
0x0A
0x100A
0x00
0x100B
0x08
0x100C
0x12
0x100D
0x34
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
pq
Poin
terto
’void
’
– 2014-04 – pointers –
49/125
1int[3
]a
={
10,
010,
0x1234
};
2int∗
p=
a;
3void
∗q
=a;
4fo
r(int
i=
0;
i<
3;++i)
{5
p++;
6q++;
7}
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0C
0x1005
0x10
0x1006
0x0A
0x1007
0x1008
0x00
0x1009
0x0A
0x100A
0x00
0x100B
0x08
0x100C
0x12
0x100D
0x34
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
pq
Poin
terto
’void
’
– 2014-04 – pointers –
49/125
1int[3
]a
={
10,
010,
0x1234
};
2int∗
p=
a;
3void
∗q
=a;
4fo
r(int
i=
0;
i<
3;++i)
{5
p++;
6q++;
7}
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0E
0x1005
0x10
0x1006
0x0A
0x1007
0x1008
0x00
0x1009
0x0A
0x100A
0x00
0x100B
0x08
0x100C
0x12
0x100D
0x34
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
pq
Poin
terto
’void
’
– 2014-04 – pointers –
49/125
1int[3
]a
={
10,
010,
0x1234
};
2int∗
p=
a;
3void
∗q
=a;
4fo
r(int
i=
0;
i<
3;++i)
{5
p++;
6q++;
7}
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0E
0x1005
0x10
0x1006
0x0B
0x1007
0x1008
0x00
0x1009
0x0A
0x100A
0x00
0x100B
0x08
0x100C
0x12
0x100D
0x34
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
pq
Poin
ters:O
bserva
tion
– 2014-04 – pointers –
50/125
•A
variable
ofpointer
typejust
storesanaddress.
•Sodovariab
lesofarray
type.
•Pointers
canpointto
acertain
type,
orto
void.
•“A
pointer
tovoid
shall
have
thesam
erepresen
tationandalig
nment
requirem
ents
asapointer
toacharacter
type.”
(6.2.5.26)
•Theeff
ectof“increm
entin
g”apointer
dependsonthetyp
epointed
to.
1int
a[2
];2
int∗
p=
a;
3++p;
//
poin
ts
toa[1
]4
void
∗q
=a;
5q
+=
sizeof(int);
//
poin
ts
toa[1
]6
++q;
//
may
poin
tin
to
the
middle
Poin
terA
rithm
etic
– 2014-04 – pointers –
51/125
1int[3
]a
={
10,
010,
0x1234
},
i=
0;
23int∗
p=
a;
//
not&a
!45
if
(a[0
]==
∗p)
i++;
6if
(a[1
]==
∗(p+1))
i++;
7if
(a[2
]==
∗(p+2))
i++;
89if
(&(a[2
])−
p==
2)
i++;
10
11
void
∗q
=a;
12
13
if
(a[2
]==
∗((int∗)(q
+(2
∗sizeof(int)))))
i++;
14
15
//
i==
5
void
assuch
does
not
have
values,
we
need
toca
st’q’here...
note:
void*
canbecasted
toeveryth
ing
Po
inters
for
Ca
llB
yR
eference
– 2014-04 – pointers –
52/125
Call
By
Referen
cew
ithP
oin
ters
– 2014-04 – pointers –
53/125
1void
f(
int
x,
int
y)
{2
x++,y++;
3}
4void
g(
int∗
p,
int∗
q)
{5
(∗p)+
+,
(∗q)+
+;
6}
7int
a=
2,
b=
5;
8f(
a,
b);
9g(
&a,&b
);...
0x1000
0x1001
0x00
0x1002
0x02
0x1003
0x00
0x1004
0x05
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x..
0x100B
0x..
0x100C
0x..
0x100D
0x..
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x..
0x1014
0x..
0x1015
0x..
0x1016
0x..
0x1017
...
ab
x
y
pq
Call
By
Referen
cew
ithP
oin
ters
– 2014-04 – pointers –
53/125
1void
f(
int
x,
int
y)
{2
x++,y++;
3}
4void
g(
int∗
p,
int∗
q)
{5
(∗p)+
+,
(∗q)+
+;
6}
7int
a=
2,
b=
5;
8f(
a,
b);
9g(
&a,&b
);...
0x1000
0x1001
0x00
0x1002
0x02
0x1003
0x00
0x1004
0x05
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x00
0x100B
0x02
0x100C
0x00
0x100D
0x05
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x..
0x1014
0x..
0x1015
0x..
0x1016
0x..
0x1017
...
Call
By
Referen
cew
ithP
oin
ters
– 2014-04 – pointers –
53/125
1void
f(
int
x,
int
y)
{2
x++,y++;
3}
4void
g(
int∗
p,
int∗
q)
{5
(∗p)+
+,
(∗q)+
+;
6}
7int
a=
2,
b=
5;
8f(
a,
b);
9g(
&a,&b
);...
0x1000
0x1001
0x00
0x1002
0x02
0x1003
0x00
0x1004
0x05
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x00
0x100B
0x03
0x100C
0x00
0x100D
0x06
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x..
0x1014
0x..
0x1015
0x..
0x1016
0x..
0x1017
...
Call
By
Referen
cew
ithP
oin
ters
– 2014-04 – pointers –
53/125
1void
f(
int
x,
int
y)
{2
x++,y++;
3}
4void
g(
int∗
p,
int∗
q)
{5
(∗p)+
+,
(∗q)+
+;
6}
7int
a=
2,
b=
5;
8f(
a,
b);
9g(
&a,&b
);...
0x1000
0x1001
0x00
0x1002
0x02
0x1003
0x00
0x1004
0x05
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x..
0x100B
0x..
0x100C
0x..
0x100D
0x..
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x..
0x1014
0x..
0x1015
0x..
0x1016
0x..
0x1017
...
Call
By
Referen
cew
ithP
oin
ters
– 2014-04 – pointers –
53/125
1void
f(
int
x,
int
y)
{2
x++,y++;
3}
4void
g(
int∗
p,
int∗
q)
{5
(∗p)+
+,
(∗q)+
+;
6}
7int
a=
2,
b=
5;
8f(
a,
b);
9g(
&a,&b
);...
0x1000
0x1001
0x00
0x1002
0x02
0x1003
0x00
0x1004
0x05
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x..
0x100B
0x..
0x100C
0x..
0x100D
0x..
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x10
0x1014
0x01
0x1015
0x10
0x1016
0x03
0x1017
...
Call
By
Referen
cew
ithP
oin
ters
– 2014-04 – pointers –
53/125
1void
f(
int
x,
int
y)
{2
x++,y++;
3}
4void
g(
int∗
p,
int∗
q)
{5
(∗p)+
+,
(∗q)+
+;
6}
7int
a=
2,
b=
5;
8f(
a,
b);
9g(
&a,&b
);...
0x1000
0x1001
0x00
0x1002
0x03
0x1003
0x00
0x1004
0x06
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x..
0x100B
0x..
0x100C
0x..
0x100D
0x..
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x10
0x1014
0x01
0x1015
0x10
0x1016
0x03
0x1017
...
Call
By
Referen
cew
ithP
oin
ters
– 2014-04 – pointers –
53/125
1void
f(
int
x,
int
y)
{2
x++,y++;
3}
4void
g(
int∗
p,
int∗
q)
{5
(∗p)+
+,
(∗q)+
+;
6}
7int
a=
2,
b=
5;
8f(
a,
b);
9g(
&a,&b
);...
0x1000
0x1001
0x00
0x1002
0x03
0x1003
0x00
0x1004
0x06
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x..
0x100B
0x..
0x100C
0x..
0x100D
0x..
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x..
0x1014
0x..
0x1015
0x..
0x1016
0x..
0x1017
...
Dyn
am
icSto
rage
&Sto
rage
Dura
tion
– 2014-04 – storage –
54/125
Dyn
am
icS
tora
ge
Allo
catio
n
– 2014-04 – storage –
55/125
AL
inked
List
– 2014-04 – storage –
56/125
data:
’A’
next:
0x1004
data:
’B’
next:
0x1001
data:
’C’
next:
0x0000
1typedef
struct
Node
{2
char
data
;3
struct
Node∗
next;
4}
Node;
56Node
c=
{’C
’,
0};
7Node
b=
{’B
’,&c
};
8Node
a=
{’A
’,&b
};
...0x1000
0x1001
’C’
0x1002
0x00
0x1003
0x00
0x1004
’B’
0x1005
0x10
0x1006
0x01
0x1007
’A’
0x1008
0x10
0x1009
0x04
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
Nodec
b.data
b.next=
&c
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
allocate
somespace
fora
Node,retu
rnits
address;
may
fail(“ou
tof
mem
ory”),mallo
c(3)yield
s0then
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x00
0x1002
0x00
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
head
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x00
0x1002
0x00
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x00
0x1002
0x00
0x1003
0x10
0x1004
0x13
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
’..’0x1014
0x..
0x1015
0x..
0x1016
0x1017
...
hlp
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x00
0x1002
0x00
0x1003
0x10
0x1004
0x13
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x..
0x1015
0x..
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x00
0x1002
0x00
0x1003
0x10
0x1004
0x13
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x10
0x1002
0x13
0x1003
0x10
0x1004
0x13
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
data:
’C’
next:
0x0000
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x10
0x1002
0x13
0x1003
0x10
0x1004
0x13
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
data:
’C’
next:
0x0000
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x10
0x1002
0x13
0x1003
0x10
0x1004
0x13
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
data:
’C’
next:
0x0000
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x10
0x1002
0x13
0x1003
0x10
0x1004
0x08
0x1005
0x1006
0x1007
0x1008
’..’0x1009
0x..
0x100A
0x..
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
data:
’C’
next:
0x0000
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x10
0x1002
0x13
0x1003
0x10
0x1004
0x08
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x..
0x100A
0x..
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
data:
’C’
next:
0x0000
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x10
0x1002
0x13
0x1003
0x10
0x1004
0x08
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
data:
’C’
next:
0x0000
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x08
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
data:
’B’
next:
0x1013
data:
’C’
next:
0x0000
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x08
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
data:
’B’
next:
0x1013
data:
’C’
next:
0x0000
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x08
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
data:
’B’
next:
0x1013
data:
’C’
next:
0x0000
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0D
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
’..’0x100E
0x..
0x100F
0x..
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
data:
’B’
next:
0x1013
data:
’C’
next:
0x0000
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0D
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
’A’
0x100E
0x..
0x100F
0x..
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
data:
’B’
next:
0x1013
data:
’C’
next:
0x0000
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0D
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
’A’
0x100E
0x10
0x100F
0x08
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
data:
’B’
next:
0x1013
data:
’C’
next:
0x0000
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x10
0x1002
0x0D
0x1003
0x10
0x1004
0x0D
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
’A’
0x100E
0x10
0x100F
0x08
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Allo
catio
n
– 2014-04 – storage –
57/125
data:
’A’
next:
0x1008
data:
’B’
next:
0x1013
data:
’C’
next:
0x0000
1typedef
struct
Node
{2
char
data
;struct
Node∗
next;
}Node;
34Node
∗head
=0,
∗hlp
;56
void
insert(
char
d)
{7
hlp
=(Node∗)mallo
c(
sizeof(Node)
);
8hlp−>data
=d;
9hlp−>next
=head;
10
head
=hlp
;11
}12
13
insert(
’C’
);
14
insert(
’B’
);
15
insert(
’A’
);
...0x1000
0x1001
0x10
0x1002
0x0D
0x1003
0x10
0x1004
0x0D
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
’A’
0x100E
0x10
0x100F
0x08
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Managem
ent
– 2014-04 – storage –
58/125
Dynam
icStorag
eAllo
cation:
•void*mallo
c(size
tsize
);
“[...]
allocates
sizebytes
andretu
rnsapointer
totheallo
catedmem
ory.Thememory
isnotinitia
lized.[...]”
•“Onerror,
[thisfunctio
n]retu
rnsNULL.”
•void
free(void*ptr
)
“[...]
freesthemem
oryspace
pointed
toby
ptr,
which
must
have
been
returned
byaprevio
uscall
tomallo
c(),[...].”
•“Otherw
ise,or
iffre
e(ptr)
has
alreadybeen
calledbefore,
undefinedbehavioroccu
rs.”
•“Ifptr
isNULL,nooperatio
nisperform
ed.”
•Nogarb
ageco
llectio
n!
Managem
entofdynam
icstorag
eisresp
onsib
ilityoftheprogrammer.
Unaccessib
le,notfree’d
mem
oryiscalled
memory
leak.
Dyn
am
icSto
rage
Managem
ent
Exa
mple
– 2014-04 – storage –
59/125
data:
’A’
next:
0x1008
data:
’B’
next:
0x1013
data:
’C’
next:
0x0000
1void
remove()
{2
if
(hlp
=head)
{3
head
=hlp−>next;
4free(hlp
);
5}
6}
7in
sert(
’C’
);
insert(
’B’
);
insert(
’A’
);
8remove();
9in
sert(
’X’
);
...0x1000
0x1001
0x10
0x1002
0x0D
0x1003
0x10
0x1004
0x0D
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
’A’
0x100E
0x10
0x100F
0x08
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Managem
ent
Exa
mple
– 2014-04 – storage –
59/125
data:
’A’
next:
0x1008
data:
’B’
next:
0x1013
data:
’C’
next:
0x0000
1void
remove()
{2
if
(hlp
=head)
{3
head
=hlp−>next;
4free(hlp
);
5}
6}
7in
sert(
’C’
);
insert(
’B’
);
insert(
’A’
);
8remove();
9in
sert(
’X’
);
...0x1000
0x1001
0x10
0x1002
0x0D
0x1003
0x10
0x1004
0x0D
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
’A’
0x100E
0x10
0x100F
0x08
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Managem
ent
Exa
mple
– 2014-04 – storage –
59/125
data:
’B’
next:
0x1013
data:
’C’
next:
0x0000
1void
remove()
{2
if
(hlp
=head)
{3
head
=hlp−>next;
4free(hlp
);
5}
6}
7in
sert(
’C’
);
insert(
’B’
);
insert(
’A’
);
8remove();
9in
sert(
’X’
);
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0D
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
’A’
0x100E
0x10
0x100F
0x08
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Managem
ent
Exa
mple
– 2014-04 – storage –
59/125
data:
’B’
next:
0x1013
data:
’C’
next:
0x0000
1void
remove()
{2
if
(hlp
=head)
{3
head
=hlp−>next;
4free(hlp
);
5}
6}
7in
sert(
’C’
);
insert(
’B’
);
insert(
’A’
);
8remove();
9in
sert(
’X’
);
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0D
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
’A’
0x100E
0x10
0x100F
0x08
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Managem
ent
Exa
mple
– 2014-04 – storage –
59/125
data:
’B’
next:
0x1013
data:
’C’
next:
0x0000
1void
remove()
{2
if
(hlp
=head)
{3
head
=hlp−>next;
4free(hlp
);
5}
6}
7in
sert(
’C’
);
insert(
’B’
);
insert(
’A’
);
8remove();
9in
sert(
’X’
);
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0D
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
’A’
0x100E
0x10
0x100F
0x08
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Managem
ent
Exa
mple
– 2014-04 – storage –
59/125
data:
’X’
next:
0x1008
data:
’B’
next:
0x1013
data:
’C’
next:
0x0000
1void
remove()
{2
if
(hlp
=head)
{3
head
=hlp−>next;
4free(hlp
);
5}
6}
7in
sert(
’C’
);
insert(
’B’
);
insert(
’A’
);
8remove();
9in
sert(
’X’
);
...0x1000
0x1001
0x10
0x1002
0x0D
0x1003
0x10
0x1004
0x0D
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
’X’
0x100E
0x10
0x100F
0x08
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icSto
rage
Managem
ent
Exa
mple
– 2014-04 – storage –
59/125
data:
’B’
next:
0x1013
data:
’C’
next:
0x0000
1void
remove()
{2
if
(hlp
=head)
{3
head
=hlp−>next;
4free(hlp
);
5}
6}
7in
sert(
’C’
);
insert(
’B’
);
insert(
’A’
);
8remove();
9in
sert(
’X’
);
...0x1000
0x1001
0x10
0x1002
0x08
0x1003
0x10
0x1004
0x0D
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
’A’
0x100E
0x10
0x100F
0x08
0x1010
’X’
0x1011
0x10
0x1012
0x08
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Dyn
am
icL
inked
List
Iteratio
n
– 2014-04 – storage –
60/125
1Node∗
find(
char
d)
{2
hlp
=head;
3while
(hlp
){
4if
(hlp−>data
==
d)
5break;
6hlp
=hlp−>next;
7}
8retu
rn
hlp
;9
}10
insert(
’C’
);
insert(
’B’
);
insert(
’A’
);
11
find(
’B’
);
//
yie
lds
0x1008
12
find(
’O’
);
//
yie
lds
0x0000,
aka.
NULL
...0x1000
0x1001
0x10
0x1002
0x0D
0x1003
0x10
0x1004
0x0D
0x1005
0x1006
0x1007
0x1008
’B’
0x1009
0x10
0x100A
0x13
0x100B
0x100C
0x100D
’A’
0x100E
0x10
0x100F
0x08
0x1010
0x1011
0x1012
0x1013
’C’
0x1014
0x00
0x1015
0x00
0x1016
0x1017
...
Poin
tersto
Stru
ct/Unio
n—
‘.’vs.
‘->
’
– 2014-04 – storage –
61/125
1typedef
struct
{2
int
x;
3int
y;
4}
coord
inate;
56coord
inate
pos=
{13,
27
};
78coord
inate∗
p=
&pos;
9
10
int
tmp;
11
12
tmp
=(∗
p).x;
13
(∗p).x
=(∗
p).y;
14
(∗p).y
=tm
p;
15
16
tmp
=p−
>x;
17
p−>x
=p−
>y;
18
p−>y
=tm
p;
Sto
rage
Du
ratio
no
fO
bjects
– 2014-04 – storage –
62/125
Sto
rage
Dura
tion
of
Objects
(6.2
.4)
– 2014-04 – storage –
63/125
•“sta
tic”–e.g
.variab
lesin
program
scope:
•live
from
program
startto
end
•ifnotexp
licitlyinitialized
,set
to0(6.7.8)
•“automatic”
–non-static
variables
inlocal
scope:
•live
from
block
entry
toexit
•notautomatically
initialised
:“initial
value[...]
isindeterm
inate”
•“allo
cated”–dynam
icobjects:
•live
from
mallo
cto
free
•notautomatically
initialised
“Ifan
object
isreferred
tooutsid
eofits
lifetime,
thebehavioris
undefined.
Thevalu
eofapointer
beco
mes
indeterm
inate
when
theobject
itpoints
toreach
estheendofits
lifetime.”
Exa
mple:
Anato
my
of
aL
inux
Pro
gra
min
Mem
ory
– 2014-04 – storage –
64/125
c©Gusta
voDuarte
2009,used
byperm
ission.
http://duartes.org/gustavo/blog/post/anatomy-of-a-program-in-memory
local
variables
livehere
mallo
c()/free()
work
here
uninitialised
global
variables,
setto
0,here
initialised
global
variables
here
program
code
liveshere
Sto
rage
Dura
tion
“A
uto
matic”
(Sim
plifi
ed)
– 2014-04 – storage –
65/125
1void
h()
{int
y;
y++;}
2void
g()
{int
x=
5;
x++;}
3int∗
f()
{int
c=
3;
g();
h();
h();
retu
rn
&c;
}45
int
a=
27,
b,
∗p;
6p
=f();
7b
=∗p;
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x00
0x1013
0x00
0x1014
0x00
0x1015
0x00
0x1016
0x00
0x1017
0x1B
...
pb
a
stackpointer
–stack
endsat
0x1012in
thiscase;
stackgrow
sdow
nward
s(to
smaller
addr.)
Sto
rage
Dura
tion
“A
uto
matic”
(Sim
plifi
ed)
– 2014-04 – storage –
65/125
1void
h()
{int
y;
y++;}
2void
g()
{int
x=
5;
x++;}
3int∗
f()
{int
c=
3;
g();
h();
h();
retu
rn
&c;
}45
int
a=
27,
b,
∗p;
6p
=f();
7b
=∗p;
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x00
0x1013
0x00
0x1014
0x00
0x1015
0x00
0x1016
0x00
0x1017
0x1B
...
pb
a
Sto
rage
Dura
tion
“A
uto
matic”
(Sim
plifi
ed)
– 2014-04 – storage –
65/125
1void
h()
{int
y;
y++;}
2void
g()
{int
x=
5;
x++;}
3int∗
f()
{int
c=
3;
g();
h();
h();
retu
rn
&c;
}45
int
a=
27,
b,
∗p;
6p
=f();
7b
=∗p;
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x00
0x1011
0x03
0x1012
0x00
0x1013
0x00
0x1014
0x00
0x1015
0x00
0x1016
0x00
0x1017
0x1B
...
cp
ba
Sto
rage
Dura
tion
“A
uto
matic”
(Sim
plifi
ed)
– 2014-04 – storage –
65/125
1void
h()
{int
y;
y++;}
2void
g()
{int
x=
5;
x++;}
3int∗
f()
{int
c=
3;
g();
h();
h();
retu
rn
&c;
}45
int
a=
27,
b,
∗p;
6p
=f();
7b
=∗p;
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x00
0x100F
0x05
0x1010
0x00
0x1011
0x03
0x1012
0x00
0x1013
0x00
0x1014
0x00
0x1015
0x00
0x1016
0x00
0x1017
0x1B
...x
pb
a
Sto
rage
Dura
tion
“A
uto
matic”
(Sim
plifi
ed)
– 2014-04 – storage –
65/125
1void
h()
{int
y;
y++;}
2void
g()
{int
x=
5;
x++;}
3int∗
f()
{int
c=
3;
g();
h();
h();
retu
rn
&c;
}45
int
a=
27,
b,
∗p;
6p
=f();
7b
=∗p;
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x00
0x100F
0x06
0x1010
0x00
0x1011
0x03
0x1012
0x00
0x1013
0x00
0x1014
0x00
0x1015
0x00
0x1016
0x00
0x1017
0x1B
...
pb
a
Sto
rage
Dura
tion
“A
uto
matic”
(Sim
plifi
ed)
– 2014-04 – storage –
65/125
1void
h()
{int
y;
y++;}
2void
g()
{int
x=
5;
x++;}
3int∗
f()
{int
c=
3;
g();
h();
h();
retu
rn
&c;
}45
int
a=
27,
b,
∗p;
6p
=f();
7b
=∗p;
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x00
0x100F
0x06
0x1010
0x00
0x1011
0x03
0x1012
0x00
0x1013
0x00
0x1014
0x00
0x1015
0x00
0x1016
0x00
0x1017
0x1B
...
xnolonger
alive!
pb
a
Sto
rage
Dura
tion
“A
uto
matic”
(Sim
plifi
ed)
– 2014-04 – storage –
65/125
1void
h()
{int
y;
y++;}
2void
g()
{int
x=
5;
x++;}
3int∗
f()
{int
c=
3;
g();
h();
h();
retu
rn
&c;
}45
int
a=
27,
b,
∗p;
6p
=f();
7b
=∗p;
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x00
0x100F
0x06
0x1010
0x00
0x1011
0x03
0x1012
0x00
0x1013
0x00
0x1014
0x00
0x1015
0x00
0x1016
0x00
0x1017
0x1B
...
(now
)y–notexp
licitlyinitialised
,thusinitial
valueisindeterm
inate
pb
a
Sto
rage
Dura
tion
“A
uto
matic”
(Sim
plifi
ed)
– 2014-04 – storage –
65/125
1void
h()
{int
y;
y++;}
2void
g()
{int
x=
5;
x++;}
3int∗
f()
{int
c=
3;
g();
h();
h();
retu
rn
&c;
}45
int
a=
27,
b,
∗p;
6p
=f();
7b
=∗p;
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x00
0x100F
0x07
0x1010
0x00
0x1011
0x03
0x1012
0x00
0x1013
0x00
0x1014
0x00
0x1015
0x00
0x1016
0x00
0x1017
0x1B
...
pb
a
Sto
rage
Dura
tion
“A
uto
matic”
(Sim
plifi
ed)
– 2014-04 – storage –
65/125
1void
h()
{int
y;
y++;}
2void
g()
{int
x=
5;
x++;}
3int∗
f()
{int
c=
3;
g();
h();
h();
retu
rn
&c;
}45
int
a=
27,
b,
∗p;
6p
=f();
7b
=∗p;
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x00
0x100F
0x07
0x1010
0x00
0x1011
0x03
0x1012
0x00
0x1013
0x00
0x1014
0x00
0x1015
0x00
0x1016
0x00
0x1017
0x1B
...
ynolonger
alive!
pb
a
Sto
rage
Dura
tion
“A
uto
matic”
(Sim
plifi
ed)
– 2014-04 – storage –
65/125
1void
h()
{int
y;
y++;}
2void
g()
{int
x=
5;
x++;}
3int∗
f()
{int
c=
3;
g();
h();
h();
retu
rn
&c;
}45
int
a=
27,
b,
∗p;
6p
=f();
7b
=∗p;
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x00
0x100F
0x07
0x1010
0x00
0x1011
0x03
0x1012
0x00
0x1013
0x00
0x1014
0x00
0x1015
0x00
0x1016
0x00
0x1017
0x1B
...
pb
a
Sto
rage
Dura
tion
“A
uto
matic”
(Sim
plifi
ed)
– 2014-04 – storage –
65/125
1void
h()
{int
y;
y++;}
2void
g()
{int
x=
5;
x++;}
3int∗
f()
{int
c=
3;
g();
h();
h();
retu
rn
&c;
}45
int
a=
27,
b,
∗p;
6p
=f();
7b
=∗p;
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x00
0x100F
0x08
0x1010
0x00
0x1011
0x03
0x1012
0x00
0x1013
0x00
0x1014
0x00
0x1015
0x00
0x1016
0x00
0x1017
0x1B
...
pb
a
Sto
rage
Dura
tion
“A
uto
matic”
(Sim
plifi
ed)
– 2014-04 – storage –
65/125
1void
h()
{int
y;
y++;}
2void
g()
{int
x=
5;
x++;}
3int∗
f()
{int
c=
3;
g();
h();
h();
retu
rn
&c;
}45
int
a=
27,
b,
∗p;
6p
=f();
7b
=∗p;
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x00
0x100F
0x08
0x1010
0x00
0x1011
0x03
0x1012
0x00
0x1013
0x00
0x1014
0x00
0x1015
0x00
0x1016
0x00
0x1017
0x1B
...
pb
a
Sto
rage
Dura
tion
“A
uto
matic”
(Sim
plifi
ed)
– 2014-04 – storage –
65/125
1void
h()
{int
y;
y++;}
2void
g()
{int
x=
5;
x++;}
3int∗
f()
{int
c=
3;
g();
h();
h();
retu
rn
&c;
}45
int
a=
27,
b,
∗p;
6p
=f();
7b
=∗p;
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x00
0x100F
0x08
0x1010
0x00
0x1011
0x03
0x1012
0x00
0x1013
0x00
0x1014
0x00
0x1015
0x00
0x1016
0x00
0x1017
0x1B
...
pb
a
Sto
rage
Dura
tion
“A
uto
matic”
(Sim
plifi
ed)
– 2014-04 – storage –
65/125
1void
h()
{int
y;
y++;}
2void
g()
{int
x=
5;
x++;}
3int∗
f()
{int
c=
3;
g();
h();
h();
retu
rn
&c;
}45
int
a=
27,
b,
∗p;
6p
=f();
7b
=∗p;
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x00
0x100F
0x08
0x1010
0x00
0x1011
0x03
0x1012
0x10
0x1013
0x10
0x1014
0x00
0x1015
0x00
0x1016
0x00
0x1017
0x1B
...
pb
a
Sto
rage
Dura
tion
“A
uto
matic”
(Sim
plifi
ed)
– 2014-04 – storage –
65/125
1void
h()
{int
y;
y++;}
2void
g()
{int
x=
5;
x++;}
3int∗
f()
{int
c=
3;
g();
h();
h();
retu
rn
&c;
}45
int
a=
27,
b,
∗p;
6p
=f();
7b
=∗p;
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x1007
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x00
0x100F
0x08
0x1010
0x00
0x1011
0x03
0x1012
0x10
0x1013
0x10
0x1014
0x??
0x1015
0x??
0x1016
0x00
0x1017
0x1B
...
prefers
toanon-alive
object,
the
behavior
isundefined
(everythingmay
happen,fro
m‘crash
’to
‘ignore’).
pb
a
Sto
rage
Cla
ssesand
Qualifi
ers
– 2014-04 – modifiers –
66/125
Sto
rage
Cla
ssS
pecifi
ers(6
.7.1
)
– 2014-04 – modifiers –
67/125
Sto
rage
Cla
ssSpecifi
ers(6
.7.1
)
– 2014-04 – modifiers –
68/125
1typedef
char
letter;
23extern
int
x;
4extern
int
f();
56static
int
x;
//
two
uses!
(−>
later)
7static
int
f();
89
10
auto
x;
//
”his
toric
”11
12
register
y;
//
”his
toric
”
Sto
rage
Cla
ssSpecifi
ers:extern
(6.7
.1)
– 2014-04 – modifiers –
69/125
1//
not
defin
ed
here
,”im
porte
d”...
2//
3extern
int
x;
4extern
void
f();
56//
decla
red
and
defin
ed
here
,”exported”
...
7//
8int
y;
9
10
int
g()
{11
x=
y=
27;
12
f();
13
}
•→
modules,
linkin
g(later)
•usually
onlyexternin
head
ers(later)
Sto
rage
Cla
ssSpecifi
ers:static
(6.7
.1)
– 2014-04 – modifiers –
70/125
1//
decla
red
and
defin
ed
here
,2
//
not
”exported”
...
3//
4static
int
x;
5static
void
g();
678int
f()
{9
static
int
a=
0;
10
a++;
11
prin
tf(
”%s\n”,
a);
12
}13
14
f();
f();
f();
//
yie
lds
1,
2,
3
Qu
alifi
ers(6
.7.3
)
– 2014-04 – modifiers –
71/125
Qualifi
ers(6
.7.3
)
– 2014-04 – modifiers –
72/125
1int
x;
23const
int
y;
45vola
tile
int
z;
67int∗
restric
tp;
//
alia
sin
g89
10
const
vola
tile
int
a;
restrict:
•“[...
lengthyform
aldefinitio
n...]”
•“[...]
Ifthese
requirem
ents
arenotmet,
then
thebehavior
isundefined.”
•→
use
extre
mely
carefully
(i.e.ifin
doubt,notat
all)
Excu
rsion:
Mem
ory
Mapped
I/O
– 2014-04 – modifiers –
73/125
•Intuitio
n:somemem
oryaddresses
arewired
tohard
ware
•writin
gto
theaddress
causes
apin
tochangelogical
value
•readingtheaddress
gives
logical
valueofapin
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x00
0x1007
0x00
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
Excu
rsion:
Mem
ory
Mapped
I/O
– 2014-04 – modifiers –
73/125
•Intuitio
n:somemem
oryaddresses
arewired
tohard
ware
•writin
gto
theaddress
causes
apin
tochangelogical
value
•readingtheaddress
gives
logical
valueofapin
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x01
0x1007
0x00
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
Excu
rsion:
Mem
ory
Mapped
I/O
– 2014-04 – modifiers –
73/125
•Intuitio
n:somemem
oryaddresses
arewired
tohard
ware
•writin
gto
theaddress
causes
apin
tochangelogical
value
•readingtheaddress
gives
logical
valueofapin
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x01
0x1007
0x01
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
Excu
rsion:
Mem
ory
Mapped
I/O
– 2014-04 – modifiers –
73/125
•Intuitio
n:somemem
oryaddresses
arewired
tohard
ware
•writin
gto
theaddress
causes
apin
tochangelogical
value
•readingtheaddress
gives
logical
valueofapin
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x01
0x1007
0x00
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
Excu
rsion:
Mem
ory
Mapped
I/O
– 2014-04 – modifiers –
73/125
•Intuitio
n:somemem
oryaddresses
arewired
tohard
ware
•writin
gto
theaddress
causes
apin
tochangelogical
value
•readingtheaddress
gives
logical
valueofapin
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x01
0x1007
0x00
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
•Thecompiler
does
notkn
ow,“m
emory
ismemory”
.
Qualifi
ers:volatile
(6.7
.3)
– 2014-04 – modifiers –
74/125
1vola
tile
char∗
out=
0x1006;
2vola
tile
char∗
in=
0x1007;
34out=
0x01;
//
switch
lamp
on
56if
(in
&0x01)
{/∗
...
∗/
}78
if
((in
&0x01)&&
(in
&0x01))
{/∗
...
∗/
}
...0x1000
0x1001
0x1002
0x1003
0x1004
0x1005
0x1006
0x00
0x1007
0x00
0x1008
0x1009
0x100A
0x100B
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x1017
...
Strin
gs
&In
put/O
utp
ut
– 2014-04 – stringsandio –
75/125
Strin
gs
– 2014-04 – stringsandio –
76/125
Strin
gs
are
0-T
ermin
ated
ch
ar
Arra
ys
– 2014-04 – stringsandio –
77/125
1char∗
msg
=”Hello
”;
2char∗
str
=msg
;
...0x1000
0x1001
0x10
0x1002
0x06
0x1003
0x1004
0x1005
0x1006
’H’
0x1007
’e’0x1008’l’
0x1009’l’
0x100A
’o’
0x100B
’\0’
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x..
0x1017
0x..
...
msg
(char)
0
Strin
gs
are
0-T
ermin
ated
ch
ar
Arra
ys
– 2014-04 – stringsandio –
77/125
1char∗
msg
=”Hello
”;
2char∗
str
=msg
;
...0x1000
0x1001
0x10
0x1002
0x06
0x1003
0x1004
0x1005
0x1006
’H’
0x1007
’e’0x1008’l’
0x1009’l’
0x100A
’o’
0x100B
’\0’
0x100C
0x100D
0x100E
0x100F
0x1010
0x1011
0x1012
0x1013
0x1014
0x1015
0x1016
0x10
0x1017
0x06
...
msg
str
(char)
0
Strin
gM
anip
ula
tion
(Annex
B)
– 2014-04 – stringsandio –
78/125
#inclu
de<strin
g.h>
provid
esam
ongothers:
•size
tstrle
n(const
char*
s)
“[...]calcu
lateslen
gthof
strings,exclu
dingtheterm
inatin
gnullbyte
(’\0’).”
•intstrcm
p(const
char*
s1,const
char*
s2)
“[...]com
pares
thetwostrin
gss1
ands2.
Itretu
rnsan
integer
lessthan,equal
to,or
greaterthan
zeroifs1
isfou
nd,
respectively,
tobeless
than,to
match
,or
begreater
than
s2.”
•char*
strcpy(char*
s1,const
char*
s2)
“Thestrcpy()
function
copies
thestrin
gpoin
tedto
bys2,
inclu
dingtheterm
inatin
gnullbyte
(’\0’),to
thebuffer
poin
tedto
bys1.”
•char*
strncp
y(char*
s1,const
char*
s2,size
tn)
Noneofthese
functio
nsallo
catesmemory!
Allo
cateandcopy:
(notC99,butPOSIX)
•char*
strdup(const
char*
s)
Inp
ut/O
utp
ut
– 2014-04 – stringsandio –
79/125
Prin
ting
– 2014-04 – stringsandio –
80/125
1#in
clu
de
<stdio
.h>
23prin
tf(
”%s−
%i−
%f\n”,
”Hello
”,
27,
3.1
4);
Tools
&M
odules
– 2014-04 – tools –
81/125
Hello
,A
gain
– 2014-04 – tools –
82/125
1#in
clu
de
<stdio
.h>
23int
g(
int
x)
{retu
rn
x/2;
}45
int
f()
{retu
rn
g(1);
}67
int
main
()
{8
prin
tf(
”Hello
World
.\n”
);
9retu
rn
f();
10
}
•%
gcc
helloworld.c
•%
ls
•a.out
helloworld.c
•%
./a.out
•Hello
World.
•%
Zoom
In:
Prep
rocessin
g,
Com
pilin
g,
Lin
king
– 2014-04 – tools –
83/125
1#in
clu
de
<stdio
.h>
23int
g(
int
x)
{retu
rn
x/2;
}45
int
f()
{retu
rn
g(1);
}67
int
main
()
{8
prin
tf(
”Hello
World
.\n”
);
9retu
rn
f();
10
}
•%
gcc
-E
helloworld.c
>helloworld.i
•%
gcc
-c
-o
helloworld.i
•%
ld
-o
helloworld
[...]
helloworld.o
[...]
•%
./helloworld
•Hello
World.
•%
Modules
– 2014-04 – tools –
84/125
1#in
clu
de
<stdio
.h>
23int
g(
int
x)
{4
retu
rn
x/2;
5}
67int
f()
{8
retu
rn
g(1);
9}
10
11
int
main
()
{12
prin
tf(
”Hello
World
.\n”
);
13
retu
rn
f();
14
}
Modules
– 2014-04 – tools –
84/125
1#in
clu
de
<stdio
.h>
23int
g(
int
x)
{4
retu
rn
x/2;
5}
67int
f()
{8
retu
rn
g(1);
9}
10
11
int
main
()
{12
prin
tf(
”Hello
World
.\n”
);
13
retu
rn
f();
14
}Split
into:
•.h(head
er):declaratio
ns
•.c:
definitio
ns,
use
head
ersto
“im
port”
declaratio
ns
Modules
– 2014-04 – tools –
84/125
1#in
clu
de
<stdio
.h>
23int
g(
int
x)
{4
retu
rn
x/2;
5}
67int
f()
{8
retu
rn
g(1);
9}
10
11
int
main
()
{12
prin
tf(
”Hello
World
.\n”
);
13
retu
rn
f();
14
}Split
into:
•.h(head
er):declaratio
ns
•.c:
definitio
ns,
use
head
ersto
“im
port”
declaratio
ns
1#ifndef
GH
2#defin
eG
H34
extern
int
5g(
int
x);
6#endif
1#ifndef
FH
2#defin
eF
H34
extern
int
5f();
6#endif
1#in
clu
de
”g.h
”23
int
g(
int
x)
{4
retu
rn
x/2;
5}
1#in
clu
de
”g.h
”2
#in
clu
de
”f.h
”34
int
f()
{5
retu
rn
g(1);
6}
1#in
clu
de
<stdio
.h>
2#in
clu
de
”f.h
”34
int
main
()
{5
prin
tf(
”Hello
World
.\n”
);
6retu
rn
f();
7}
g.h
f.h
g.c
f.c
helloworld.c
Modules
At
Work
– 2014-04 – tools –
85/125
preprocess
&co
mpile
:
•%gcc
-c
g.cf.c
\helloworld.c
•%ls
*.o
•f.o
g.ohelloworld.o
link:
•%gcc
g.o
f.ohelloworld.o
exe
cute:
•%./a.out
•Hello
World.
1#ifndef
GH
2#defin
eG
H34
extern
int
5g(
int
x);
6#endif
1#ifndef
FH
2#defin
eF
H34
extern
int
5f();
6#endif
1#in
clu
de
”g.h
”23
int
g(
int
x)
{4
retu
rn
x/2;
5}
1#in
clu
de
”g.h
”2
#in
clu
de
”f.h
”34
int
f()
{5
retu
rn
g(1);
6}
1#in
clu
de
<stdio
.h>
2#in
clu
de
”f.h
”34
int
main
()
{5
prin
tf(
”Hello
World
.\n”
);
6retu
rn
f();
7}
g.h
f.h
g.c
f.c
helloworld.c
Modules
At
Work
– 2014-04 – tools –
85/125
preprocess
&co
mpile
:
•%gcc
-c
g.cf.c
\helloworld.c
•%ls
*.o
•f.o
g.ohelloworld.o
link:
•%gcc
g.o
f.ohelloworld.o
exe
cute:
•%./a.out
•Hello
World.
1#ifndef
GH
2#defin
eG
H34
extern
int
5g(
int
x);
6#endif
1#ifndef
FH
2#defin
eF
H34
extern
int
5f();
6#endif
1#in
clu
de
”g.h
”23
int
g(
int
x)
{4
retu
rn
x/2;
5}
1#in
clu
de
”g.h
”2
#in
clu
de
”f.h
”34
int
f()
{5
retu
rn
g(1);
6}
1#in
clu
de
<stdio
.h>
2#in
clu
de
”f.h
”34
int
main
()
{5
prin
tf(
”Hi!\
n”
);
6retu
rn
f();
7}
g.h
f.h
g.c
f.c
helloworld.c
Modules
At
Work
– 2014-04 – tools –
85/125
preprocess
&co
mpile
:
•%gcc
-c
g.cf.c
\helloworld.c
•%ls
*.o
•f.o
g.ohelloworld.o
link:
•%gcc
g.o
f.ohelloworld.o
exe
cute:
•%./a.out
•Hello
World.
fixandre-build
:
•%gcc
-c
helloworld.c
•%gcc
g.o
f.ohelloworld.o
•%./a.out
•Hi!
1#ifndef
GH
2#defin
eG
H34
extern
int
5g(
int
x);
6#endif
1#ifndef
FH
2#defin
eF
H34
extern
int
5f();
6#endif
1#in
clu
de
”g.h
”23
int
g(
int
x)
{4
retu
rn
x/2;
5}
1#in
clu
de
”g.h
”2
#in
clu
de
”f.h
”34
int
f()
{5
retu
rn
g(1);
6}
1#in
clu
de
<stdio
.h>
2#in
clu
de
”f.h
”34
int
main
()
{5
prin
tf(
”Hi!\
n”
);
6retu
rn
f();
7}
g.h
f.h
g.c
f.c
helloworld.c
Prep
rocessin
g
– 2014-04 – tools –
86/125
1#in
clu
de
<stdio
.h>
2#in
clu
de
”f.h
”34
int
main
()
{5
prin
tf(
”Hello
World
.\n”
);
6retu
rn
f();
7}•
%gcc
-E
helloworld.c
-o
helloworld.i
1#
1”hello
world
.c”
2#
1”<
comman
d−lin
e>”
3#
1”hello
world
.c”
4#
1”/usr/in
clu
de/stdio
.h”
13
45
#28
”/usr/in
clu
de/stdio
.h”
34
6#
1”/usr/in
clu
de/fe
atures.h
”1
34
7#
323
”/usr/in
clu
de/fe
atures.h
”3
48
#1
”/usr/in
clu
de/x86
64−lin
ux−gnu/bits/pre
defs
.h”
13
49
#324
”/usr/in
clu
de/fe
atures.h
”2
34
10
#356
”/usr/in
clu
de/fe
atures.h
”3
411
#1
”/usr/in
clu
de/x86
64−lin
ux−gnu/sys/cdefs
.h”
13
412
#359
”/usr/in
clu
de/x86
64−lin
ux−gnu/sys/cdefs
.h”
34
13
#1
”/usr/in
clu
de/x86
64−lin
ux−gnu/bits/word
size.h
”1
34
14
#360
”/usr/in
clu
de/x86
64−lin
ux−gnu/sys/cdefs
.h”
23
415
#357
”/usr/in
clu
de/fe
atures.h
”2
34
16
#388
”/usr/in
clu
de/fe
atures.h
”3
417
#1
”/usr/in
clu
de/x86
64−lin
ux−gnu/gnu/stubs.h
”1
34
18
19
20
21
#1
”/usr/in
clu
de/x86
64−lin
ux−gnu/bits/word
size.h
”1
34
22
#5
”/usr/in
clu
de/x86
64−lin
ux−gnu/gnu/stubs.h
”2
34
23
24
[...]
25
26
extern
int
ftrylo
ckfile
(FILE
∗stre
am
)attrib
ute
((
nothro
w))
;27
28
29
extern
void
funlo
ckfile
(FILE
∗stre
am
)attrib
ute
((
nothro
w));
30
#936
”/usr/in
clu
de/stdio
.h”
34
31
32
#2
”hello
world
.c”
233
#1
”f.h
”1
34
35
36
37
extern
int
38
f();
39
#3
”hello
world
.c”
240
41
int
main
()
{42
prin
tf(
”Hello
World
.\n”
);
43
retu
rn
f();
44
}
helloworld.c
helloworld.i
Prep
rocessin
gD
irectives(6
.10)
– 2014-04 – tools –
87/125
1#in
clu
de
<stdio
.h>
2#in
clu
de
”battery
.h”
34#defin
ePI
3.1
415
56#defin
eDEBUG
7#ifdef
DEBUG
8fprin
tf(
stderr
,”honk\n”
);
9#endif
10
11
#if
GNUC
>=
312
#defin
epure
attrib
ute
((pure
))
13
#else
14
#defin
epure
/∗
no
pure
∗/
15
#endif
16
17
extern
int
f()
pure
;
Lin
king
– 2014-04 – tools –
88/125
provides:
int
g(int)
needs:
./.
provides:
int
f()
needs:
int
g(int)
providesint
main()
needs:
int
f(int)
int
printf(const
char*,...)
provides:
int
printf(const
char*,...)
...
needs:
...
g.o
f.o
helloworld.o
libc.a
Lin
king
– 2014-04 – tools –
88/125
provides:
int
g(int)
needs:
./.
provides:
int
f()
needs:
int
g(int)
providesint
main()
needs:
int
f(int)
int
printf(const
char*,...)
provides:
int
printf(const
char*,...)
...
needs:
...
g.o
f.o
helloworld.o
libc.a
Lin
king
– 2014-04 – tools –
88/125
provides:
int
g(int)
needs:
./.
provides:
int
f()
needs:
int
g(int)
providesint
main()
needs:
int
f(int)
int
printf(const
char*,...)
provides:
int
printf(const
char*,...)
...
needs:
...
g.o
f.o
helloworld.o
libc.a
Lin
king
– 2014-04 – tools –
88/125
provides:
int
g(int)
needs:
./.
provides:
int
f()
needs:
int
g(int)
providesint
main()
needs:
int
f(int)
int
printf(const
char*,...)
provides:
int
printf(const
char*,...)
...
needs:
...
g.o
f.o
helloworld.o
libc.a
Lin
king
– 2014-04 – tools –
88/125
provides:
int
g(int)
needs:
./.
provides:
int
f()
needs:
int
g(int)
providesint
main()
needs:
int
f(int)
int
printf(const
char*,...)
provides:
int
printf(const
char*,...)
...
needs:
...
g.o
f.o
helloworld.o
libc.a
a.out
Com
piler
– 2014-04 – tools –
89/125
gcc
[OPTIO
N]...
infile...
-E–prepro
cesson
ly
-c–com
pile
only,
don
’tlink
Exa
mple:gcc
-cmain.c—
produces
main.o
-ooutfile
–write
outputto
outfile
Exa
mple:gcc
-c-o
x.o
main.c—
produces
x.o
-g–adddebuginform
ation
-W,-W
all,
...–enable
warn
ings
-Idir
–adddirto
inclu
depath
forsearch
inghead
ers
-Ldir
–adddirto
library
path
forsearch
inglibraries
-Dmacro
[=defn]–definemacro
(todefn)
Exa
mple:gcc
-DDEBUG
-DMAGICNUMBER=27
-l library
linkagain
stliblibrary.{a,so},
order
matters
Exa
mple:gcc
a.ob.o
main.o
-lxy
→cf.
man
gcc
gdb(1
),ddd(1
),nm
(1),
make(1
)
– 2014-04 – tools –
90/125
•CommandLineDebugger:gdb
a.out
[core]
•GUIDebugger:
ddd
a.out
[core]
(works
best
with
debugginginform
ationcompiled
in(gcc
-g))
•Insp
ect
Object
File
s:
nm
a.o
•Build
Utility
:
make
See
battery
contro
llerexercise
foran
example.
Core
Dum
ps
– 2014-04 – tools –
91/125
c©Gusta
voDuarte
2009,used
byperm
ission.
http://duartes.org/gustavo/blog/post/anatomy-of-a-program-in-memory
•Reca
ll:Anatom
yof
aLinuxProgram
inMem
ory
•Core
dump:(basically)
thismem
orywritten
toafile.
Core
Dum
ps
– 2014-04 – tools –
91/125
c©Gusta
voDuarte
2009,used
byperm
ission.
http://duartes.org/gustavo/blog/post/anatomy-of-a-program-in-memory
•Reca
ll:Anatom
yof
aLinuxProgram
inMem
ory
•Core
dump:(basically)
thismem
orywritten
toafile.
1int
main
()
{2
int
∗p;
3∗p
=27;
4retu
rn
0;
5}
1%
gcc
−g
core
.c
2%
limit
core
dumpsize
3core
dumpsize
0kbytes
4%
limit
core
dumpsize
1g
5%
./a.out
6Segmenta
tion
fault
(core
dumped
)7
%ls
−lh
core
8−rw
−−−−−−−
1user
user
232K
Feb
29
11:1
1core
9%
gdb
a.out
core
10
GNU
gdb
(GDB)
7.4.1
−debian
11
[...]
12
Core
was
genera
ted
by
‘./a.out’.
13
Program
term
inated
with
sig
nal
11,
Segmenta
tion
fault
.14
#0
0x00000000004004b4
inmain
()
at
core
.c:3
15
3∗p
=27;
16
(gdb)
pp
17
$1
=(in
t∗)
0x0
18
(gdb)
q
Form
al
Meth
ods
for
C
– 2014-04 – assert –
92/125
Co
rrectness
an
dR
equ
iremen
ts
– 2014-04 – assert –
93/125
Correctn
ess
– 2014-04 – assert –
94/125
•Correctn
essisdefined
with
resp
ect
toaspecifi
cation.
•A
program
(functio
n,...)
isco
rrect
(wrt.
specifi
cationϕ)
ifandonly
ifitsatisfi
esϕ.
•Definitio
nof“satisfi
es”:in
aminute.
Examples:
•ϕ1 :
theretu
rnvalu
eis10divid
edby
param
eter(if
param
eternot0)
•ϕ2 :
thevalu
eofvariab
lexis“alw
ays”strictly
greater
than
3
•ϕ3 :
thevalu
eofiincreases
ineach
loopiteratio
n
•...
Com
mon
Pattern
s
– 2014-04 – assert –
95/125
•State
Invaria
nts:
“at
this
program
point,thevalu
eofpmust
notbeNULL”
“at
allpro
gram
points,
thevalu
eofpmust
notbeNULL”
(cf.sequence
points
(Annex
C))
•Data
Invaria
nts:
“thevalu
eofnmust
bethelen
gth
ofs”
•(F
unctio
n)Pre/Post
Conditio
ns:
Pre-C
onditio
n:theparam
etermust
notbe0
Post-C
onditio
n:theretu
rnvalu
eis10divid
edby
theparam
eter
•LoopInvaria
nts:
“thevalu
eofiisbetw
een0andarray
length
minus1”
Po
or
Ma
n’s
Req
uirem
ents
Sp
ecifica
tion
aka
.H
ow
toF
orm
alize
Req
uirem
ents
inC
?
– 2014-04 – assert –
96/125
Dia
gnostics
(7.2
)
– 2014-04 – assert –
97/125
1#in
clu
de
<assert.h>
2void
assert(
/∗
scala
r∗/
expressio
n);
Dia
gnostics
(7.2
)
– 2014-04 – assert –
97/125
1#in
clu
de
<assert.h>
2void
assert(
/∗
scala
r∗/
expressio
n);
•“Theassert
macro
puts
diag
nostic
testsinto
program
s;[...]
When
itisexecu
ted,ifexpression(w
hich
shall
have
ascalar
type)
isfalse
(that
is,compares
equal
to0),
theassert
macro
•writes
inform
ationab
outtheparticu
larcall
that
failed[...]
onthe
standard
errorstream
inan
implem
entatio
n-defined
format.
•Itthen
callstheabort
functio
n.”
Dia
gnostics
(7.2
)
– 2014-04 – assert –
97/125
1#in
clu
de
<assert.h>
2void
assert(
/∗
scala
r∗/
expressio
n);
•“Theassert
macro
puts
diag
nostic
testsinto
program
s;[...]
When
itisexecu
ted,ifexpression(w
hich
shall
have
ascalar
type)
isfalse
(that
is,compares
equal
to0),
theassert
macro
•writes
inform
ationab
outtheparticu
larcall
that
failed[...]
onthe
standard
errorstream
inan
implem
entatio
n-defined
format.
•Itthen
callstheabort
functio
n.”
Pitfall:
•Ifmacro
NDEBUGisdefinedwhen
inclu
ding<asse
rt.h>,
expressionis
notevaluated(th
usshould
besid
e-effect
free).
abort
(7.2
0.4
.1)
– 2014-04 – assert –
98/125
1#in
clu
de
<stdlib
.h>
23void
abort
();
•“Theab
ortfunctio
ncau
sesabnorm
alpro
gram
terminatio
nto
occu
r,unless
[...]
•[...]
Anim
plem
entatio
n-defined
formofthestatu
sunsuccessfu
lterm
inatio
nisretu
rned
tothehost
enviro
nmentby
mean
softhefunctio
ncall
raise(SIGABRT).”
(→Core
Dumps)
Com
mon
Pattern
sw
ithassert
– 2014-04 – assert –
99/125
•State
Invaria
nts:
“at
this
program
point,thevalu
eofpmust
notbeNULL”
“at
allpro
gram
points,
thevalu
eofpmust
notbeNULL”
(cf.sequence
points
(Annex
C))
•Data
Invaria
nts:
“thevalu
eofnmust
bethelen
gth
ofs”
•(F
unctio
n)Pre/Post
Conditio
ns:
Pre-C
onditio
n:theparam
etermust
notbe0
Post-C
onditio
n:theretu
rnvalu
eis10divid
edby
theparam
eter
•LoopInvaria
nts:
“thevalu
eofiisbetw
een0andarray
length
minus1”
Sta
teIn
varia
nts
with
<assert.h
>
– 2014-04 – assert –
100/125
1void
f()
{2
int∗
p=
(int∗)mallo
c(sizeof(int));
34if
(!p)
5retu
rn;
67assert(p);
//
assu
me
pis
valid
from
here
8//
...
9}
10
11
void
g()
{12
Node∗
p=
find(
’a’
);
13
14
assert(p);
//
we
inserted
’a’
befo
re15
//
...
16
}
Data
Inva
riants
with
<assert.h
>
– 2014-04 – assert –
101/125
1typedef
struct
{2
char∗
s;
3int
n;
4}
str;
56str∗
constru
ct(
char∗
s)
{7
str∗
x=
(str∗)mallo
c(
sizeof(str)
);
8//
...
9assert(
(x−
>s==
NULL
&&
x−>n
==
−1)
10
||(x−
>n
=strle
n(
x−>s
))
);
11
}
Pre/P
ost
Conditio
ns
with
<assert.h
>
– 2014-04 – assert –
102/125
1int
f(
int
x)
{2
assert(
x!=
0);
//
pre−conditio
n34
int
r=
10/x;
56assert(
r==
10/x
);
//
post−
condititio
n78
retu
rn
r;
9}
Loop
Inva
riants
with
<assert.h
>
– 2014-04 – assert –
103/125
1void
f(
int
a[]
,int
n)
{2
int
i=
0;
34//
hold
sbefo
reth
eloop
5assert(
0<=
i&&
i<=
n);
6assert(
i<
1||
a[i−1]==
0);
78while
(i<
n)
{9
//
hold
sbefo
reeach
iteratio
n10
assert(
0<=
i&&
i<=
n);
11
assert(
i<
1||
a[i−1]==
0);
12
13
a[i+
+]=
0;
14
}15
//
hold
saft
er
exitin
gth
eloop
16
assert(
0<=
i&&
i<=
n);
17
assert(
i<
1||
a[i−1]==
0);
18
19
retu
rn;
20
}
Old
Varia
bles,
Ghost
Varia
bles
– 2014-04 – assert –
104/125
1void
xorS
wap(
unsigned
int∗
a,
unsigned
int∗
b)
{2
#ifndefNDEBUG
3unsigned
int
∗old
a=
a,
∗old
b=
b;
4#endif
5assert(
a&&
b);
assert(
a!=
b);
//
pre−conditio
n67
∗a
=∗a
+∗b;
8∗b
=∗a
−∗b;
9∗a
=∗a
−∗b;
10
11
assert(
∗a
==
∗old
b&&
∗b
==
∗old
a);
//
post−
con−
12
assert(
a==
old
a&&
b==
old
b);
//
ditio
n13
}
Outlo
ok
– 2014-04 – assert –
105/125
•Someverifi
cationtoolssim
ply
verifyfor
eachassertstatem
ent:
When
executed
,expressionisnotfalse.
•Someverifi
cationtoolssupport
sophisticated
requirem
ents
specifi
cation
languages
likeACSLwith
explicit
support
for
•pre/
post
conditio
ns
•ghost
variables,
old
values
•data
invarian
ts
•loopinvarian
ts
•...
Dep
end
ab
leVerifi
catio
n(Ja
ckson
)
– 2014-04 – assert –
106/125
Dep
endability
– 2014-04 – assert –
107/125
•“Theprogram
hasbeenverifi
ed.”
tellsus
Dep
endability
– 2014-04 – assert –
107/125
•“Theprogram
hasbeenverifi
ed.”
tellsusnotvery
much
.
Dep
endability
– 2014-04 – assert –
107/125
•“Theprogram
hasbeenverifi
ed.”
tellsusnotvery
much
.
•Onewants
tokn
ow(an
dshould
state):
Dep
endability
– 2014-04 – assert –
107/125
•“Theprogram
hasbeenverifi
ed.”
tellsusnotvery
much
.
•Onewants
tokn
ow(an
dshould
state):
•W
hich
specifi
catio
nshave
been
consid
ered?
Dep
endability
– 2014-04 – assert –
107/125
•“Theprogram
hasbeenverifi
ed.”
tellsusnotvery
much
.
•Onewants
tokn
ow(an
dshould
state):
•W
hich
specifi
catio
nshave
been
consid
ered?
•Under
which
assu
mptio
nswas
theverifi
cationconducted
?
•Platform
assumptio
ns:
finite
word
s(size?),
math
ematical
integ
ers,...
•Enviro
nmentassu
mptio
ns,inputvalu
es,...
Assu
mptio
nsare
often
implicit,
“inthetool”!
Dep
endability
– 2014-04 – assert –
107/125
•“Theprogram
hasbeenverifi
ed.”
tellsusnotvery
much
.
•Onewants
tokn
ow(an
dshould
state):
•W
hich
specifi
catio
nshave
been
consid
ered?
•Under
which
assu
mptio
nswas
theverifi
cationconducted
?
•Platform
assumptio
ns:
finite
word
s(size?),
math
ematical
integ
ers,...
•Enviro
nmentassu
mptio
ns,inputvalu
es,...
Assu
mptio
nsare
often
implicit,
“inthetool”!
•Andwhatdoesverifi
catio
nmeanafter
all?
•In
somecontexts:
testin
g.
•In
somecontexts:
review.
•In
somecontexts:
model-ch
eck
ingpro
cedure.
(“Weverifi
edtheprogram
!”–“What
did
thetoolsay?”
–“Verifi
cationfailed
.”)
•In
somecontexts:
model-ch
eck
ingtoolcla
imsco
rrectn
ess.
Com
mon
Erro
rs
– 2014-04 – pitfalls –
108/125
Distin
guish
– 2014-04 – pitfalls –
109/125
Most
generic
erro
rsboildow
nto:
•specifi
edbutunwantedbehaviour,
e.g.under/
overfl
ows
•initia
lisatio
nissu
es
e.g.automatic
block
scopeobjects
•unsp
ecifi
edbehaviour(J.1
)e.g
.ord
erofevalu
ationin
somecases
•undefinedbehaviour(J.2
)
•im
plementatio
ndefinedbehaviour(J.3
)
Confo
rmance
(4)
– 2014-04 – pitfalls –
110/125
•“A
program
that
is
•correct
inall
other
aspects,
•op
eratingon
correctdata,
•con
tainingunsp
ecifi
edbehavio
r
shall
beacorrect
program
andact
inaccord
ance
with
5.1.2.3.(P
rogram
Execu
tion)
•A
conform
ingpro
gram
isonethat
isaccep
table
toaconform
ing
implem
entatio
n.
•Strictly
conform
ingpro
gram
sare
inten
ded
tobemaxim
allyportab
leam
ong
conform
ingim
plem
entatio
ns.
•Anim
plem
entatio
n[ofC,acompiler]
shall
beacco
mpanied
byadocument
that
defines
allim
plem
entatio
n-defined
andlocale-sp
ecificcharacteristics
andall
extensio
ns.
Over-
an
dU
nd
erflo
ws
– 2014-04 – pitfalls –
111/125
Over-
and
Underfl
ow
s,C
astin
g
– 2014-04 – pitfalls –
112/125
•Notspecifi
cto
C...
1void
f(
short
a,
int
b)
{2
a=
b;
//
typin
gok,
but...
3}
45short
a;
//
provisio
nin
g,
implic
itcast
6if
(++a
<0)
{/∗
no
∗/
}78
if
(++i>
MAX
INT)
{9
/∗
no
∗/
}10
11
12
int
e=
0;
13
14
void
set
error()
{e++;}
15
void
cle
ar
error()
{e
=0;
}16
17
void
g()
{if
(e)
{/∗
...
∗/
}}
Initia
lisatio
n(6
.7.8
)
– 2014-04 – pitfalls –
113/125
Initia
lisatio
n(6
.7.8
)
– 2014-04 – pitfalls –
114/125
•“Ifan
object
that
has
automatic
storageduratio
nisnotinitialized
explicitly,
itsvalu
eisindeterm
inate.”
1void
f()
{2
int
a;
34prin
tf(
”%i\
n”,
a);
//
surprise...
5}
Un
specifi
edB
eha
viou
r(J.1
)
– 2014-04 – pitfalls –
115/125
Unsp
ecified
Beh
avio
ur
(J.1)
– 2014-04 – pitfalls –
116/125
Each
implem
entatio
n(ofacompiler)
documents
how
thechoice
ismade.
Forexample
•wheth
ertwostrin
gliterals
resultin
distin
ctarrays
(6.4.5)
•theord
erin
which
thefunction
design
ator,argu
ments,
andsubexpression
swith
intheargu
ments
areevalu
atedin
afunction
call(6.5.2.2)
•thelayou
tof
storagefor
function
param
eters(6.9.1)
•theresu
ltof
roundingwhen
thevalu
eisou
tof
range
(7.12.9.5,...)
•theord
erandcon
tiguity
ofstorage
allocated
bysuccessive
callsto
malloc(7.20.3)
•etc.
pp.
1char
a[]
=”hello
”,
b[]
=”hello
”;
//
a==
b?
23i=
0;
f(++i,++i,++i
);
//
f(1,2
,3)?
45int
g()
{int
a,
b;
}//
&a
>&b
?67
int∗
p=
mallo
c(sizeof(int));
8int∗
q=
mallo
c(sizeof(int));
//
q>
p?
Un
defi
ned
Beh
avio
ur
(J.2)
– 2014-04 – pitfalls –
117/125
Undefi
ned
Beh
avio
ur
(3.4
.3)
– 2014-04 – pitfalls –
118/125
“Behavio
ur,uponuse
ofanon-portab
leor
erroneouspro
gram
constru
ctor
oferro
neousdata,
forwhich
thisIntern
ational
Stan
dard
imposes
no
requirem
ents.”
“Possib
leundefinedbehaviourrangesfro
m
•ignorin
gthesitu
ationcompletely
with
unpredicta
ble
results,
•to
behavin
gdurin
gtra
nsla
tionorprogram
execu
tion
inadocumented
manner
characteristic
oftheenviro
nment
(with
orwith
outtheissu
ance
ofadiag
nostic
messag
e),
•to
terminatin
gatra
nsla
tionorexecu
tion
(with
theissu
ance
ofadiag
nostic
messag
e).”
“Anexam
ple
ofundefined
behavio
uristhebehavio
uronintegeroverflow.”
Undefi
ned
Beh
avio
ur
(J.2)
– 2014-04 – pitfalls –
119/125
More
examples:
•an
identifi
er[...]
contain
san
invalid
multibyte
character
(5.2.1.2)
Undefi
ned
Beh
avio
ur
(J.2)
– 2014-04 – pitfalls –
119/125
More
examples:
•an
identifi
er[...]
contain
san
invalid
multibyte
character
(5.2.1.2)
•an
object
isreferred
toou
tsideof
itslifetim
e(6.2.4)
Undefi
ned
Beh
avio
ur
(J.2)
– 2014-04 – pitfalls –
119/125
More
examples:
•an
identifi
er[...]
contain
san
invalid
multibyte
character
(5.2.1.2)
•an
object
isreferred
toou
tsideof
itslifetim
e(6.2.4)
•thevalu
eof
apoin
terto
anob
jectwhole
lifetimehas
ended
isused
(6.2.4)
Undefi
ned
Beh
avio
ur
(J.2)
– 2014-04 – pitfalls –
119/125
More
examples:
•an
identifi
er[...]
contain
san
invalid
multibyte
character
(5.2.1.2)
•an
object
isreferred
toou
tsideof
itslifetim
e(6.2.4)
•thevalu
eof
apoin
terto
anob
jectwhole
lifetimehas
ended
isused
(6.2.4)
•con
versionto
orfrom
aninteger
typepro
duces
avalu
eou
tsidetheran
gethat
canberepresen
ted(6.3.1.4)
Undefi
ned
Beh
avio
ur
(J.2)
– 2014-04 – pitfalls –
119/125
More
examples:
•an
identifi
er[...]
contain
san
invalid
multibyte
character
(5.2.1.2)
•an
object
isreferred
toou
tsideof
itslifetim
e(6.2.4)
•thevalu
eof
apoin
terto
anob
jectwhole
lifetimehas
ended
isused
(6.2.4)
•con
versionto
orfrom
aninteger
typepro
duces
avalu
eou
tsidetheran
gethat
canberepresen
ted(6.3.1.4)
•con
versionbetw
eentwopoin
tertyp
espro
duces
aresu
ltthat
isincorrectly
aligned
(6.3.2.3)
Undefi
ned
Beh
avio
ur
(J.2)
– 2014-04 – pitfalls –
119/125
More
examples:
•an
identifi
er[...]
contain
san
invalid
multibyte
character
(5.2.1.2)
•an
object
isreferred
toou
tsideof
itslifetim
e(6.2.4)
•thevalu
eof
apoin
terto
anob
jectwhole
lifetimehas
ended
isused
(6.2.4)
•con
versionto
orfrom
aninteger
typepro
duces
avalu
eou
tsidetheran
gethat
canberepresen
ted(6.3.1.4)
•con
versionbetw
eentwopoin
tertyp
espro
duces
aresu
ltthat
isincorrectly
aligned
(6.3.2.3)
•theprogram
attempts
tomodify
astrin
gliteral
(6.4.5)
Undefi
ned
Beh
avio
ur
(J.2)
– 2014-04 – pitfalls –
119/125
More
examples:
•an
identifi
er[...]
contain
san
invalid
multibyte
character
(5.2.1.2)
•an
object
isreferred
toou
tsideof
itslifetim
e(6.2.4)
•thevalu
eof
apoin
terto
anob
jectwhole
lifetimehas
ended
isused
(6.2.4)
•con
versionto
orfrom
aninteger
typepro
duces
avalu
eou
tsidetheran
gethat
canberepresen
ted(6.3.1.4)
•con
versionbetw
eentwopoin
tertyp
espro
duces
aresu
ltthat
isincorrectly
aligned
(6.3.2.3)
•theprogram
attempts
tomodify
astrin
gliteral
(6.4.5)
•an
exception
alcon
dition
occu
rsdurin
gtheevalu
ationof
anexpression
(6.5)
Undefi
ned
Beh
avio
ur
(J.2)
– 2014-04 – pitfalls –
119/125
More
examples:
•an
identifi
er[...]
contain
san
invalid
multibyte
character
(5.2.1.2)
•an
object
isreferred
toou
tsideof
itslifetim
e(6.2.4)
•thevalu
eof
apoin
terto
anob
jectwhole
lifetimehas
ended
isused
(6.2.4)
•con
versionto
orfrom
aninteger
typepro
duces
avalu
eou
tsidetheran
gethat
canberepresen
ted(6.3.1.4)
•con
versionbetw
eentwopoin
tertyp
espro
duces
aresu
ltthat
isincorrectly
aligned
(6.3.2.3)
•theprogram
attempts
tomodify
astrin
gliteral
(6.4.5)
•an
exception
alcon
dition
occu
rsdurin
gtheevalu
ationof
anexpression
(6.5)
•thevalu
eof
thesecon
dop
erandof
the/or
%op
eratoriszero
(6.5.5)
Undefi
ned
Beh
avio
ur
(J.2)
– 2014-04 – pitfalls –
119/125
More
examples:
•an
identifi
er[...]
contain
san
invalid
multibyte
character
(5.2.1.2)
•an
object
isreferred
toou
tsideof
itslifetim
e(6.2.4)
•thevalu
eof
apoin
terto
anob
jectwhole
lifetimehas
ended
isused
(6.2.4)
•con
versionto
orfrom
aninteger
typepro
duces
avalu
eou
tsidetheran
gethat
canberepresen
ted(6.3.1.4)
•con
versionbetw
eentwopoin
tertyp
espro
duces
aresu
ltthat
isincorrectly
aligned
(6.3.2.3)
•theprogram
attempts
tomodify
astrin
gliteral
(6.4.5)
•an
exception
alcon
dition
occu
rsdurin
gtheevalu
ationof
anexpression
(6.5)
•thevalu
eof
thesecon
dop
erandof
the/or
%op
eratoriszero
(6.5.5)
•poin
tersthat
donot
poin
tinto,
orjust
beyon
d,thesam
earray
object
aresubtracted
(6.5.6)
Undefi
ned
Beh
avio
ur
(J.2)
– 2014-04 – pitfalls –
119/125
More
examples:
•an
identifi
er[...]
contain
san
invalid
multibyte
character
(5.2.1.2)
•an
object
isreferred
toou
tsideof
itslifetim
e(6.2.4)
•thevalu
eof
apoin
terto
anob
jectwhole
lifetimehas
ended
isused
(6.2.4)
•con
versionto
orfrom
aninteger
typepro
duces
avalu
eou
tsidetheran
gethat
canberepresen
ted(6.3.1.4)
•con
versionbetw
eentwopoin
tertyp
espro
duces
aresu
ltthat
isincorrectly
aligned
(6.3.2.3)
•theprogram
attempts
tomodify
astrin
gliteral
(6.4.5)
•an
exception
alcon
dition
occu
rsdurin
gtheevalu
ationof
anexpression
(6.5)
•thevalu
eof
thesecon
dop
erandof
the/or
%op
eratoriszero
(6.5.5)
•poin
tersthat
donot
poin
tinto,
orjust
beyon
d,thesam
earray
object
aresubtracted
(6.5.6)
•Anarray
subscrip
tisou
tof
range
[...](6.5.6)
Undefi
ned
Beh
avio
ur
(J.2)
– 2014-04 – pitfalls –
119/125
More
examples:
•an
identifi
er[...]
contain
san
invalid
multibyte
character
(5.2.1.2)
•an
object
isreferred
toou
tsideof
itslifetim
e(6.2.4)
•thevalu
eof
apoin
terto
anob
jectwhole
lifetimehas
ended
isused
(6.2.4)
•con
versionto
orfrom
aninteger
typepro
duces
avalu
eou
tsidetheran
gethat
canberepresen
ted(6.3.1.4)
•con
versionbetw
eentwopoin
tertyp
espro
duces
aresu
ltthat
isincorrectly
aligned
(6.3.2.3)
•theprogram
attempts
tomodify
astrin
gliteral
(6.4.5)
•an
exception
alcon
dition
occu
rsdurin
gtheevalu
ationof
anexpression
(6.5)
•thevalu
eof
thesecon
dop
erandof
the/or
%op
eratoriszero
(6.5.5)
•poin
tersthat
donot
poin
tinto,
orjust
beyon
d,thesam
earray
object
aresubtracted
(6.5.6)
•Anarray
subscrip
tisou
tof
range
[...](6.5.6)
•theprogram
removes
thedefinition
ofamacro
whose
nam
ebegin
swith
anunderscore
andeith
eran
uppercase
letteror
anoth
erunderscore
(7.1.3)
Undefi
ned
Beh
avio
ur
(J.2)
– 2014-04 – pitfalls –
119/125
More
examples:
•an
identifi
er[...]
contain
san
invalid
multibyte
character
(5.2.1.2)
•an
object
isreferred
toou
tsideof
itslifetim
e(6.2.4)
•thevalu
eof
apoin
terto
anob
jectwhole
lifetimehas
ended
isused
(6.2.4)
•con
versionto
orfrom
aninteger
typepro
duces
avalu
eou
tsidetheran
gethat
canberepresen
ted(6.3.1.4)
•con
versionbetw
eentwopoin
tertyp
espro
duces
aresu
ltthat
isincorrectly
aligned
(6.3.2.3)
•theprogram
attempts
tomodify
astrin
gliteral
(6.4.5)
•an
exception
alcon
dition
occu
rsdurin
gtheevalu
ationof
anexpression
(6.5)
•thevalu
eof
thesecon
dop
erandof
the/or
%op
eratoriszero
(6.5.5)
•poin
tersthat
donot
poin
tinto,
orjust
beyon
d,thesam
earray
object
aresubtracted
(6.5.6)
•Anarray
subscrip
tisou
tof
range
[...](6.5.6)
•theprogram
removes
thedefinition
ofamacro
whose
nam
ebegin
swith
anunderscore
andeith
eran
uppercase
letteror
anoth
erunderscore
(7.1.3)
•etc.
pp.
Null-P
oin
ter
– 2014-04 – pitfalls –
120/125
1int
main
()
{2
int
∗p;
3∗p
=27;
4retu
rn
0;
5}
Null-P
oin
ter
– 2014-04 – pitfalls –
120/125
1int
main
()
{2
int
∗p;
3∗p
=27;
4retu
rn
0;
5}
•“A
ninteger
constan
texpression
with
thevalu
e0,
orsuch
anexpression
castto
typevoid*,
iscalled
anullpointerco
nsta
nt.
[...]”
•“T
hemacro
NULLisdefined
in<std
def.h
>(an
doth
erhead
ers)as
anullpoin
tercon
stant;see
7.17.”
•“A
mon
gtheinvalid
values
fordereferen
cingapoin
terby
theunary
*op
eratorare
anullpoin
ter,[...]”
(6.5.3.2)
Seg
men
tatio
nV
iola
tion
– 2014-04 – pitfalls –
121/125
1int
main
()
{2
int
∗p
=(int∗)0
x12345678;
3∗p
=27;
45∗(int∗)(((void
∗)p)
+1)
=13;
6retu
rn
0;
7}
Seg
men
tatio
nV
iola
tion
– 2014-04 – pitfalls –
121/125
1int
main
()
{2
int
∗p
=(int∗)0
x12345678;
3∗p
=27;
45∗(int∗)(((void
∗)p)
+1)
=13;
6retu
rn
0;
7}
•Modern
operatin
gsystem
sprovid
ememory
protectio
n.
•Accessin
gmem
orywhich
thepro
cessisnot
allowed
toaccess
isob
servedby
theop
eratingsystem
.
•Typically
aninstan
ceof
“accessingan
object
outsid
eits
lifetime”.
•But:
other
way
rounddoes
not
hold
,accessin
gan
object
outsid
eits
lifetimedoes
not
imply
asegm
entation
violation.
Seg
men
tatio
nV
iola
tion
– 2014-04 – pitfalls –
121/125
1int
main
()
{2
int
∗p
=(int∗)0
x12345678;
3∗p
=27;
45∗(int∗)(((void
∗)p)
+1)
=13;
6retu
rn
0;
7}
•Modern
operatin
gsystem
sprovid
ememory
protectio
n.
•Accessin
gmem
orywhich
thepro
cessisnot
allowed
toaccess
isob
servedby
theop
eratingsystem
.
•Typically
aninstan
ceof
“accessingan
object
outsid
eits
lifetime”.
•But:
other
way
rounddoes
not
hold
,accessin
gan
object
outsid
eits
lifetimedoes
not
imply
asegm
entation
violation.
•Som
eplatform
s(e.g.
SPARC):
unalign
edmem
oryaccess,
i.e.ou
tsideword
bou
ndaries,
not
supported
byhard
ware
(“buserror”).
Operatin
gsystem
notifi
espro
cess,defau
lthandler:
terminate,
dumpcore.
Imp
lemen
tatio
n-D
efin
edB
eha
viou
r(J.3
)
– 2014-04 – pitfalls –
122/125
Implem
enta
tion-D
efined
Beh
avio
ur
(J.3)
– 2014-04 – pitfalls –
123/125
“A
conform
ingim
plem
entatio
nisreq
uired
todocumentits
choice
ofbehavior
ineach
oftheareas
listedin
thissubclau
se.Thefollow
ingare
implem
entatio
n-defined:”
Implem
enta
tion-D
efined
Beh
avio
ur
(J.3)
– 2014-04 – pitfalls –
123/125
“A
conform
ingim
plem
entatio
nisreq
uired
todocumentits
choice
ofbehavior
ineach
oftheareas
listedin
thissubclau
se.Thefollow
ingare
implem
entatio
n-defined:”
•J.3.2
Environ
ment,e.g.
Theset
ofsign
als,their
semantics,
andtheir
defau
lthandling(7.14).
Implem
enta
tion-D
efined
Beh
avio
ur
(J.3)
– 2014-04 – pitfalls –
123/125
“A
conform
ingim
plem
entatio
nisreq
uired
todocumentits
choice
ofbehavior
ineach
oftheareas
listedin
thissubclau
se.Thefollow
ingare
implem
entatio
n-defined:”
•J.3.2
Environ
ment,e.g.
Theset
ofsign
als,their
semantics,
andtheir
defau
lthandling(7.14).
•J.3.3
Identifi
ers,e.g.
Thenumber
ofsign
ifican
tinitial
characters
inan
identifi
er(5.2.4.1,
6.4.2).
Implem
enta
tion-D
efined
Beh
avio
ur
(J.3)
– 2014-04 – pitfalls –
123/125
“A
conform
ingim
plem
entatio
nisreq
uired
todocumentits
choice
ofbehavior
ineach
oftheareas
listedin
thissubclau
se.Thefollow
ingare
implem
entatio
n-defined:”
•J.3.2
Environ
ment,e.g.
Theset
ofsign
als,their
semantics,
andtheir
defau
lthandling(7.14).
•J.3.3
Identifi
ers,e.g.
Thenumber
ofsign
ifican
tinitial
characters
inan
identifi
er(5.2.4.1,
6.4.2).
•J.3.4
Characters,
e.g.Thenumber
ofbits
inabyte
(3.6).
Implem
enta
tion-D
efined
Beh
avio
ur
(J.3)
– 2014-04 – pitfalls –
123/125
“A
conform
ingim
plem
entatio
nisreq
uired
todocumentits
choice
ofbehavior
ineach
oftheareas
listedin
thissubclau
se.Thefollow
ingare
implem
entatio
n-defined:”
•J.3.2
Environ
ment,e.g.
Theset
ofsign
als,their
semantics,
andtheir
defau
lthandling(7.14).
•J.3.3
Identifi
ers,e.g.
Thenumber
ofsign
ifican
tinitial
characters
inan
identifi
er(5.2.4.1,
6.4.2).
•J.3.4
Characters,
e.g.Thenumber
ofbits
inabyte
(3.6).
•J.3.5
Integers,
e.g.Anyexten
ded
integer
types
that
existin
theim
plem
entation
(6.2.5).
Implem
enta
tion-D
efined
Beh
avio
ur
(J.3)
– 2014-04 – pitfalls –
123/125
“A
conform
ingim
plem
entatio
nisreq
uired
todocumentits
choice
ofbehavior
ineach
oftheareas
listedin
thissubclau
se.Thefollow
ingare
implem
entatio
n-defined:”
•J.3.2
Environ
ment,e.g.
Theset
ofsign
als,their
semantics,
andtheir
defau
lthandling(7.14).
•J.3.3
Identifi
ers,e.g.
Thenumber
ofsign
ifican
tinitial
characters
inan
identifi
er(5.2.4.1,
6.4.2).
•J.3.4
Characters,
e.g.Thenumber
ofbits
inabyte
(3.6).
•J.3.5
Integers,
e.g.Anyexten
ded
integer
types
that
existin
theim
plem
entation
(6.2.5).
•J.3.6
Floatin
gPoin
t,e.g.
Theaccu
racyof
thefloatin
g-poin
top
erations[...]
(5.2.4.2.2).
Implem
enta
tion-D
efined
Beh
avio
ur
(J.3)
– 2014-04 – pitfalls –
123/125
“A
conform
ingim
plem
entatio
nisreq
uired
todocumentits
choice
ofbehavior
ineach
oftheareas
listedin
thissubclau
se.Thefollow
ingare
implem
entatio
n-defined:”
•J.3.2
Environ
ment,e.g.
Theset
ofsign
als,their
semantics,
andtheir
defau
lthandling(7.14).
•J.3.3
Identifi
ers,e.g.
Thenumber
ofsign
ifican
tinitial
characters
inan
identifi
er(5.2.4.1,
6.4.2).
•J.3.4
Characters,
e.g.Thenumber
ofbits
inabyte
(3.6).
•J.3.5
Integers,
e.g.Anyexten
ded
integer
types
that
existin
theim
plem
entation
(6.2.5).
•J.3.6
Floatin
gPoin
t,e.g.
Theaccu
racyof
thefloatin
g-poin
top
erations[...]
(5.2.4.2.2).
•J.3.7
Arrays
andPoin
ters,e.g.
Theresu
ltof
convertin
gapoin
terto
aninteger
orvice
versa(6.3.2.3).
Implem
enta
tion-D
efined
Beh
avio
ur
(J.3)
– 2014-04 – pitfalls –
123/125
“A
conform
ingim
plem
entatio
nisreq
uired
todocumentits
choice
ofbehavior
ineach
oftheareas
listedin
thissubclau
se.Thefollow
ingare
implem
entatio
n-defined:”
•J.3.2
Environ
ment,e.g.
Theset
ofsign
als,their
semantics,
andtheir
defau
lthandling(7.14).
•J.3.3
Identifi
ers,e.g.
Thenumber
ofsign
ifican
tinitial
characters
inan
identifi
er(5.2.4.1,
6.4.2).
•J.3.4
Characters,
e.g.Thenumber
ofbits
inabyte
(3.6).
•J.3.5
Integers,
e.g.Anyexten
ded
integer
types
that
existin
theim
plem
entation
(6.2.5).
•J.3.6
Floatin
gPoin
t,e.g.
Theaccu
racyof
thefloatin
g-poin
top
erations[...]
(5.2.4.2.2).
•J.3.7
Arrays
andPoin
ters,e.g.
Theresu
ltof
convertin
gapoin
terto
aninteger
orvice
versa(6.3.2.3).
•etc.
pp.
Loca
leand
Com
mon
Exten
sions
(J.4,J.5
)
– 2014-04 – pitfalls –
124/125
•J.4
Locale-sp
ecificbehavio
ur
•J.5
Commonexten
sions
“Thefollow
ingexten
sionsare
widely
used
inmanysystem
s,butare
not
portab
leto
allim
plem
entatio
ns.”
Referen
ces
– 2014-04 – main –
125/125
[ISO,1999]ISO
(1999).
Program
minglan
guages
–C.Tech
nical
Report
ISO/IEC9899:1999,ISO.Seco
ndeditio
n,1999-12-01.
