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cmemset

Usage of memset() in c

I have written a small program to get used to memset() operation:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>

int main()
{
    int arr[10], i;
    int t = INT_MAX;
    memset(arr, t, sizeof(arr));
    for (i = 0; i < 10; i++)
        printf("%d\t",arr[i]);

    printf("%d",t);
    return 0;
}

The result of the above program is:

-1 -1 -1 -1 -1 -1 -1 -1 -1 -1

2147483647

What is the behaviour of the memset() in the above program? Why is it setting the array elements to -1?

Solution

  • memset only takes the lower eight bits of the value and fills the whole buffer with these bits. The lower eight bits of MAX_INT are all ones (0xFF), and thus the array is afterwards filled with all ones. For signed integers, this is -1.