How to handle realloc when it fails due to memory?

Question

Question says it all but here is an example:

typedef struct mutable_t{
    int count, max;
    void **data;
} mutable_t;


void pushMutable(mutable_t *m, voi         


        

Answer 1

The standard technique is to introduce a new variable to hold the return from realloc. You then only overwrite your input variable if it succeeds:

tmp = realloc(orig, newsize);
if (tmp == NULL)
{
    // could not realloc, but orig still valid
}
else
{
    orig = tmp;
}

Answer 2

There's also another subtle error that can come from realloc. The memory leak coming from returned NULL pointer is rather well known (but quite rare to stumble upon). I had in my program a crash once in a while that came from a realloc call. I had a dynamic structure that adjusted its size automatically with a realloc resembling this one:

m->data = realloc(m->data, m->max * sizeof(void*)); 

The error I made was to not check for m->max == 0, which freed the memory area. And made from my m->data pointer a stale one.

I know it's a bit off-topic but this was the only real issue I ever had with realloc.