C: Expanding an array with malloc
Use realloc, but you have to allocate the array with malloc first. You're allocating it on the stack in the above example.
size_t myarray_size = 1000; mystruct* myarray = malloc(myarray_size * sizeof(mystruct)); myarray_size += 1000; mystruct* myrealloced_array = realloc(myarray, myarray_size * sizeof(mystruct)); if (myrealloced_array) { myarray = myrealloced_array; } else { // deal with realloc failing because memory could not be allocated. }
You want to use realloc (as other posters have already pointed out). But unfortunately, the other posters have not shown you how to correctly use it:
POINTER *tmp_ptr = realloc(orig_ptr, new_size);if (tmp_ptr == NULL){ // realloc failed, orig_ptr still valid so you can clean up}else{ // Only overwrite orig_ptr once you know the call was successful orig_ptr = tmp_ptr;}
You need to use tmp_ptr
so that if realloc
fails, you don't lose the original pointer.
No, you can't. You can't change the size of an array on the stack once it's defined: that's kind of what fixed-size means. Or a global array, either: it's not clear from your code sample where myarray
is defined.
You could malloc
a 1000-element array, and later resize it with realloc
. This can return you a new array, containing a copy of the data from the old one, but with extra space at the end.