Arrays : Clearing array contents (zeroing)

Question

Clearing array contents (zeroing)

Answer 1

Sometimes it's necessary to set an array to zero, after the initialization has been done.

#include <stdlib.h>         /* for EXIT_SUCCESS */

#define ARRLEN (10)

int main(void)

{  

int array[ARRLEN];          /* Allocated but not initialised, as not defined static or global. */

  size_t i;  

for(i = 0; i < ARRLEN; ++i)  

{    

array[i] = 0;  

}

return EXIT_SUCCESS;

}

An common short cut to the above loop is to use memset() from <string.h>. Passing array as shown below makes it decay to a pointer to its 1st element.

memset(array, 0, ARRLEN * sizeof (int));     /* Use size explicitly provided type (int here). */

or

memset(array, 0, ARRLEN * sizeof *array);    /* Use size of type the pointer is pointing to. */

As in this example array is an array and not just a pointer to an array's 1st element (see Array length on why this is important) a third option to 0-out the array is possible:

 memset(array, 0, sizeof array);      /* Use size of the array itself. */