malloc memory to a pointer to pointer

Question

I have came across this problem when using pointer to pointer to a char:

void setmemory(char** p, int num)
{
    *p=(char*)malloc(num);
}

    void test(void)
           


        

Answer 1

The orignal code is passing in the location of where the caller wants the string pointer put. If you pass in only a 'char*', the caller will pass by value the contents of the callers location - probably some uninitialized value.

If the callee has to return a string, or other indirected struct, you need both asterisks so that the callee can return a pointer into the callers pointer variable.

Does that make sense? It did to me, but then again, I wrote it.