Generic function to free 2d arrays with cleanup attribute in C
I've recently discovered __attribute__((cleanup)) which is very handy. I have made a generic function to free any type of pointer and it works fine.
#define _autofree_ __attribute__ ((cleanup(free_pointer)))
...
void free_pointer(void *pointer)
{
free(*(void **) pointer);
}
But it's not as easy when it comes to freeing 2d arrays. As far as I know cleanup uses a pointer to the given pointer for stack restriction reasons, and it's a good thing because it doesn't use a copy of it at any point. Anyway, Dereferencing a (void **) cast to pass through "derefencing void *" errors works but then if I do
#define _autofree2d_ __attribute__ ((cleanup(free_pointer_array)))
...
void free_pointer_array(void *pointer_array)
{
for (size_t i = 0 ; (void **) pointer_array[i] ; ++i)
free(*(void **) pointer_array[i]);
free(*(void ***) pointer_array);
}
I end up dereferencing a void * because of the bracketed [i]. Also this just doesn't look right.
I'm also trying doing it in a less generic way using char pointers (as I'm currently working with a word array) and it compiles but gives we a segfault because of an invalid free.
void free_pointer_array(char ***array)
{
for (size_t i = 0 ; *array[i] ; ++i)
free(*array[i]);
free(**array); // Tried using ***array and got
// "pointer from integer without a cast" error
}
c arrays attributes malloc free
asked Nov 20 '18 at 20:24
RenardRenard
166
add a comment |
I've recently discovered __attribute__((cleanup)) which is very handy. I have made a generic function to free any type of pointer and it works fine.
#define _autofree_ __attribute__ ((cleanup(free_pointer)))
...
void free_pointer(void *pointer)
{
free(*(void **) pointer);
}
But it's not as easy when it comes to freeing 2d arrays. As far as I know cleanup uses a pointer to the given pointer for stack restriction reasons, and it's a good thing because it doesn't use a copy of it at any point. Anyway, Dereferencing a (void **) cast to pass through "derefencing void *" errors works but then if I do
#define _autofree2d_ __attribute__ ((cleanup(free_pointer_array)))
...
void free_pointer_array(void *pointer_array)
{
for (size_t i = 0 ; (void **) pointer_array[i] ; ++i)
free(*(void **) pointer_array[i]);
free(*(void ***) pointer_array);
}
I end up dereferencing a void * because of the bracketed [i]. Also this just doesn't look right.
I'm also trying doing it in a less generic way using char pointers (as I'm currently working with a word array) and it compiles but gives we a segfault because of an invalid free.
void free_pointer_array(char ***array)
{
for (size_t i = 0 ; *array[i] ; ++i)
free(*array[i]);
free(**array); // Tried using ***array and got
// "pointer from integer without a cast" error
}
c arrays attributes malloc free
asked Nov 20 '18 at 20:24
RenardRenard
166
If you allocate an actual array, instead of an array of pointers to one-dimensional arrays, you could free the array with a single call tofree(). See stackoverflow.com/questions/42094465/…
– Andrew Henle
Nov 20 '18 at 20:34
add a comment |
I've recently discovered __attribute__((cleanup)) which is very handy. I have made a generic function to free any type of pointer and it works fine.
#define _autofree_ __attribute__ ((cleanup(free_pointer)))
...
void free_pointer(void *pointer)
{
free(*(void **) pointer);
}
But it's not as easy when it comes to freeing 2d arrays. As far as I know cleanup uses a pointer to the given pointer for stack restriction reasons, and it's a good thing because it doesn't use a copy of it at any point. Anyway, Dereferencing a (void **) cast to pass through "derefencing void *" errors works but then if I do
#define _autofree2d_ __attribute__ ((cleanup(free_pointer_array)))
...
void free_pointer_array(void *pointer_array)
{
for (size_t i = 0 ; (void **) pointer_array[i] ; ++i)
free(*(void **) pointer_array[i]);
free(*(void ***) pointer_array);
}
I end up dereferencing a void * because of the bracketed [i]. Also this just doesn't look right.
I'm also trying doing it in a less generic way using char pointers (as I'm currently working with a word array) and it compiles but gives we a segfault because of an invalid free.
void free_pointer_array(char ***array)
{
for (size_t i = 0 ; *array[i] ; ++i)
free(*array[i]);
free(**array); // Tried using ***array and got
// "pointer from integer without a cast" error
}
c arrays attributes malloc free
asked Nov 20 '18 at 20:24
RenardRenard
166
I've recently discovered __attribute__((cleanup)) which is very handy. I have made a generic function to free any type of pointer and it works fine.
#define _autofree_ __attribute__ ((cleanup(free_pointer)))
...
void free_pointer(void *pointer)
{
free(*(void **) pointer);
}
But it's not as easy when it comes to freeing 2d arrays. As far as I know cleanup uses a pointer to the given pointer for stack restriction reasons, and it's a good thing because it doesn't use a copy of it at any point. Anyway, Dereferencing a (void **) cast to pass through "derefencing void *" errors works but then if I do
#define _autofree2d_ __attribute__ ((cleanup(free_pointer_array)))
...
void free_pointer_array(void *pointer_array)
{
for (size_t i = 0 ; (void **) pointer_array[i] ; ++i)
free(*(void **) pointer_array[i]);
free(*(void ***) pointer_array);
}
I end up dereferencing a void * because of the bracketed [i]. Also this just doesn't look right.
I'm also trying doing it in a less generic way using char pointers (as I'm currently working with a word array) and it compiles but gives we a segfault because of an invalid free.
void free_pointer_array(char ***array)
{
for (size_t i = 0 ; *array[i] ; ++i)
free(*array[i]);
free(**array); // Tried using ***array and got
// "pointer from integer without a cast" error
}
c arrays attributes malloc free
c arrays attributes malloc free
asked Nov 20 '18 at 20:24
RenardRenard
166
asked Nov 20 '18 at 20:24
RenardRenard
166
asked Nov 20 '18 at 20:24
RenardRenard
166
asked Nov 20 '18 at 20:24
RenardRenard
166
asked Nov 20 '18 at 20:24
RenardRenard
166
166
If you allocate an actual array, instead of an array of pointers to one-dimensional arrays, you could free the array with a single call tofree(). See stackoverflow.com/questions/42094465/…
– Andrew Henle
Nov 20 '18 at 20:34
add a comment |
If you allocate an actual array, instead of an array of pointers to one-dimensional arrays, you could free the array with a single call tofree(). See stackoverflow.com/questions/42094465/…
– Andrew Henle
Nov 20 '18 at 20:34
If you allocate an actual array, instead of an array of pointers to one-dimensional arrays, you could free the array with a single call to
free(). See stackoverflow.com/questions/42094465/…– Andrew Henle
Nov 20 '18 at 20:34
If you allocate an actual array, instead of an array of pointers to one-dimensional arrays, you could free the array with a single call to
free(). See stackoverflow.com/questions/42094465/…– Andrew Henle
Nov 20 '18 at 20:34
add a comment |
1 Answer
1
active
oldest
votes
As mentioned by Andrew Henle in the comments, my method of allocation was the problem. I was making a look-up table rather than an actual 2d array. Using the method described here : Correctly allocating multi-dimensional arrays, I can simply use my original _autofree_ macro for arrays of any dimension.
answered Nov 21 '18 at 20:02
RenardRenard
166
add a comment |
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1 Answer
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1 Answer
1
active
oldest
votes
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oldest
votes
active
oldest
votes
As mentioned by Andrew Henle in the comments, my method of allocation was the problem. I was making a look-up table rather than an actual 2d array. Using the method described here : Correctly allocating multi-dimensional arrays, I can simply use my original _autofree_ macro for arrays of any dimension.
answered Nov 21 '18 at 20:02
RenardRenard
166
add a comment |
As mentioned by Andrew Henle in the comments, my method of allocation was the problem. I was making a look-up table rather than an actual 2d array. Using the method described here : Correctly allocating multi-dimensional arrays, I can simply use my original _autofree_ macro for arrays of any dimension.
answered Nov 21 '18 at 20:02
RenardRenard
166
add a comment |
As mentioned by Andrew Henle in the comments, my method of allocation was the problem. I was making a look-up table rather than an actual 2d array. Using the method described here : Correctly allocating multi-dimensional arrays, I can simply use my original _autofree_ macro for arrays of any dimension.
answered Nov 21 '18 at 20:02
RenardRenard
166
As mentioned by Andrew Henle in the comments, my method of allocation was the problem. I was making a look-up table rather than an actual 2d array. Using the method described here : Correctly allocating multi-dimensional arrays, I can simply use my original _autofree_ macro for arrays of any dimension.
answered Nov 21 '18 at 20:02
RenardRenard
166
answered Nov 21 '18 at 20:02
RenardRenard
166
answered Nov 21 '18 at 20:02
RenardRenard
166
answered Nov 21 '18 at 20:02
RenardRenard
166
166
add a comment |
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If you allocate an actual array, instead of an array of pointers to one-dimensional arrays, you could free the array with a single call to
free(). See stackoverflow.com/questions/42094465/…– Andrew Henle
Nov 20 '18 at 20:34