Segfault while accessing dynamicly allocated C struct array
I have the following struct that is defined in the following way
typedef struct _abcd {
int a;
unsigned long b;
void (*c)(int);
int d;
} abcd_t, *abcd;
Now i have the following code
static abcd foo
int set_size(int size){
foo = malloc(sizeof(abcd) * size);
}
This code for some reason gives me segfault when accessing some of the properties of array members.
But i have noticed that if i change the malloc line to the following - it fixes the issue
foo = malloc(sizeof(foo[0]) * size);
I find it strange as obviously sizeof(foo[0]) = sizeof(abcd)
So what is exactly the difference here?
Thanks
c malloc dynamic-arrays
asked Nov 15 '18 at 0:50
Dor DaliDor Dali
235
add a comment |
I have the following struct that is defined in the following way
typedef struct _abcd {
int a;
unsigned long b;
void (*c)(int);
int d;
} abcd_t, *abcd;
Now i have the following code
static abcd foo
int set_size(int size){
foo = malloc(sizeof(abcd) * size);
}
This code for some reason gives me segfault when accessing some of the properties of array members.
But i have noticed that if i change the malloc line to the following - it fixes the issue
foo = malloc(sizeof(foo[0]) * size);
I find it strange as obviously sizeof(foo[0]) = sizeof(abcd)
So what is exactly the difference here?
Thanks
c malloc dynamic-arrays
asked Nov 15 '18 at 0:50
Dor DaliDor Dali
235
add a comment |
I have the following struct that is defined in the following way
typedef struct _abcd {
int a;
unsigned long b;
void (*c)(int);
int d;
} abcd_t, *abcd;
Now i have the following code
static abcd foo
int set_size(int size){
foo = malloc(sizeof(abcd) * size);
}
This code for some reason gives me segfault when accessing some of the properties of array members.
But i have noticed that if i change the malloc line to the following - it fixes the issue
foo = malloc(sizeof(foo[0]) * size);
I find it strange as obviously sizeof(foo[0]) = sizeof(abcd)
So what is exactly the difference here?
Thanks
c malloc dynamic-arrays
asked Nov 15 '18 at 0:50
Dor DaliDor Dali
235
I have the following struct that is defined in the following way
typedef struct _abcd {
int a;
unsigned long b;
void (*c)(int);
int d;
} abcd_t, *abcd;
Now i have the following code
static abcd foo
int set_size(int size){
foo = malloc(sizeof(abcd) * size);
}
This code for some reason gives me segfault when accessing some of the properties of array members.
But i have noticed that if i change the malloc line to the following - it fixes the issue
foo = malloc(sizeof(foo[0]) * size);
I find it strange as obviously sizeof(foo[0]) = sizeof(abcd)
So what is exactly the difference here?
Thanks
c malloc dynamic-arrays
c malloc dynamic-arrays
asked Nov 15 '18 at 0:50
Dor DaliDor Dali
235
asked Nov 15 '18 at 0:50
Dor DaliDor Dali
235
edited Nov 15 '18 at 0:56
Dor Dali
asked Nov 15 '18 at 0:50
Dor DaliDor Dali
235
asked Nov 15 '18 at 0:50
Dor DaliDor Dali
235
asked Nov 15 '18 at 0:50
Dor DaliDor Dali
235
235
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
obviously
sizeof(foo[0]) = sizeof(abcd)
It is not the same since you typedefed abcd to be a *pointer* to struct _abcd.
Use
foo = malloc(sizeof(*foo) * size);
to have robust code even if the type of foo should change at some point.
Your
foo = malloc(sizeof(foo[0]) * size);
is essentially the same since foo[0] is just syntactic sugar for *(foo + 0) which becomes *foo.
answered Nov 15 '18 at 0:55
SwordfishSwordfish
10.1k11436
add a comment |
The bug is you're allocating sizeof(abcd) and that's a pointer, not a struct. You want sizeof(abcd_t) or sizeof(*abcd).
answered Nov 15 '18 at 0:56
John ZwinckJohn Zwinck
153k17177296
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
obviously
sizeof(foo[0]) = sizeof(abcd)
It is not the same since you typedefed abcd to be a *pointer* to struct _abcd.
Use
foo = malloc(sizeof(*foo) * size);
to have robust code even if the type of foo should change at some point.
Your
foo = malloc(sizeof(foo[0]) * size);
is essentially the same since foo[0] is just syntactic sugar for *(foo + 0) which becomes *foo.
answered Nov 15 '18 at 0:55
SwordfishSwordfish
10.1k11436
add a comment |
obviously
sizeof(foo[0]) = sizeof(abcd)
It is not the same since you typedefed abcd to be a *pointer* to struct _abcd.
Use
foo = malloc(sizeof(*foo) * size);
to have robust code even if the type of foo should change at some point.
Your
foo = malloc(sizeof(foo[0]) * size);
is essentially the same since foo[0] is just syntactic sugar for *(foo + 0) which becomes *foo.
answered Nov 15 '18 at 0:55
SwordfishSwordfish
10.1k11436
add a comment |
obviously
sizeof(foo[0]) = sizeof(abcd)
It is not the same since you typedefed abcd to be a *pointer* to struct _abcd.
Use
foo = malloc(sizeof(*foo) * size);
to have robust code even if the type of foo should change at some point.
Your
foo = malloc(sizeof(foo[0]) * size);
is essentially the same since foo[0] is just syntactic sugar for *(foo + 0) which becomes *foo.
answered Nov 15 '18 at 0:55
SwordfishSwordfish
10.1k11436
obviously
sizeof(foo[0]) = sizeof(abcd)
It is not the same since you typedefed abcd to be a *pointer* to struct _abcd.
Use
foo = malloc(sizeof(*foo) * size);
to have robust code even if the type of foo should change at some point.
Your
foo = malloc(sizeof(foo[0]) * size);
is essentially the same since foo[0] is just syntactic sugar for *(foo + 0) which becomes *foo.
answered Nov 15 '18 at 0:55
SwordfishSwordfish
10.1k11436
answered Nov 15 '18 at 0:55
SwordfishSwordfish
10.1k11436
answered Nov 15 '18 at 0:55
SwordfishSwordfish
10.1k11436
answered Nov 15 '18 at 0:55
SwordfishSwordfish
10.1k11436
10.1k11436
add a comment |
add a comment |
The bug is you're allocating sizeof(abcd) and that's a pointer, not a struct. You want sizeof(abcd_t) or sizeof(*abcd).
answered Nov 15 '18 at 0:56
John ZwinckJohn Zwinck
153k17177296
add a comment |
The bug is you're allocating sizeof(abcd) and that's a pointer, not a struct. You want sizeof(abcd_t) or sizeof(*abcd).
answered Nov 15 '18 at 0:56
John ZwinckJohn Zwinck
153k17177296
add a comment |
The bug is you're allocating sizeof(abcd) and that's a pointer, not a struct. You want sizeof(abcd_t) or sizeof(*abcd).
answered Nov 15 '18 at 0:56
John ZwinckJohn Zwinck
153k17177296
The bug is you're allocating sizeof(abcd) and that's a pointer, not a struct. You want sizeof(abcd_t) or sizeof(*abcd).
answered Nov 15 '18 at 0:56
John ZwinckJohn Zwinck
153k17177296
answered Nov 15 '18 at 0:56
John ZwinckJohn Zwinck
153k17177296
answered Nov 15 '18 at 0:56
John ZwinckJohn Zwinck
153k17177296
answered Nov 15 '18 at 0:56
John ZwinckJohn Zwinck
153k17177296
153k17177296
add a comment |
add a comment |
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