C Language Clearing array contents (zeroing)


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). */


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. */