How to free the memory after return the array?

[ggyyree]

I have got some codes written in C, it returns an array allocated using 'calloc'. However, as far as I know, we need to do the 'free'. But if we free the array before return, it will return nothing. If we don't do free, we will get a memory leak somehow in the future. May I ask how to do it please? Here is the codes:

Rbt * mcrbt_CreeRbtVide(int32_t taillemax)
{
int32_t i;
Rbt * T = (Rbt *)calloc(1,sizeof(Rbt) + taillemax*sizeof(RbtElt));

T->max = taillemax;
T->util = 0;
T->maxutil = 0;
T->nil = &(T->elts[0]);
T->nil->left = T->nil->right = T->nil->parent = NULL;
T->root = T->nil;

return T;
// My question is how to free this T then?
}

[moorecm]

Document the requirement that users of mcrbt_CreeRbtVide have ownership of the return and are responsible for the free.

[webJose]

Or you can opt to request the caller of the function for the appropriate buffer, like the Windows API. I prefer this method.

Rbt* mcrbt_CreeRbtVide(int32_t taillemax, void *lpBuffer, size_t *lpBuffSize)
{
    //Calculate the required buffer size.  If it is less than *lpBuffSize, don't perform the operation
    //and return in *lpBuffSize the required size.
    size_t requiredSize = sizeof(Rbt) + taillemax * sizeof(RbtElt);
    if (*lpBuffSize < requiredSize)
    {
        *lpBuffSize = requiredSize;
        return NULL;
    }
    //At this point, all you have to do is cast the lpBuffer pointer as (Rbt*) and you are good to go.
    .....
}

//Callers of the function are then required to provide their own buffers, like this:
size_t buffSize = 0;
void *lpBuffer = NULL;
mcrbt_CreeRbtVide(someValue, lpBuffer, &buffSize);
lpBuffer = malloc(buffSize);
//Now the buffer is ready and good to go.  Repeat the function call.
mcrbt_CreeRbtVide(someValue, lpBuffer, &buffSize);
//Use the data
....
//Now release the buffer.
free(lpBuffer);

This is my favorite choice because the caller is free to use whatever memory allocator function he/she requires, like Windows' HeapAlloc(), or COM's IMalloc, etc.

[stereoMatching]

why don't just encapsulate the data and let the destructor free your memory?
Or just use smart pointer to do all of the dirty jobs?

[webJose]

@stereoMatching: It is C, not C++. But yes, that would be ideal. :-)

[stereoMatching]

sorry, I should read the post carefully.