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, void *object)
{
    if(m->count == m->max){
        m->max *= 2;
        m->data = realloc(m->data, m->max * sizeof(void*));
    }
    // how to handle oom??
    m->data[m->count++] = object;
}

How can I handle running out of memory and not NULL out all of my data?

edit - let's assume there is something which could be done e.g. free up some memory somewhere or at least tell the user "you can't do that - you're out of memory". Ideally I would like to leave what was allocated there.

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;
}