Initializing a malloc'ed string index to NULL

Question

For example, say I just created a char **strings by using malloc.

How would I set each index strings[i] to NULL? Is it initially set to NULL? Because when I check with another function for an index equal to NULL, like if(strings[i] == NULL); It never seems to work. Any help? Sorry I'm new to dynamic memory..

Answer 1

NULL is usually defined as a macro that expands to (void *)0

You can use calloc to allocate and initialize to zero. Be sure to use the correct number of parentheses.

char* buffer = calloc(4, sizeof(char));

if(*buffer == 0) {
    printf("%s\n", "*buffer == 0");
}

Answer 2

malloc() only allocates memory. You should use calloc() which allocates memory and zeroes the allocated memory.

Being an array of pointers, each element will now be equal to NULL .

char **strings = calloc(1024, sizeof *string);
if(strings[1] == NULL)
    printf("%s", "yes. NULL");