strncpy test

test_strncpy.c

#include <stdio.h>
#include <string.h>
/*
output:
       w's: 77 77 77 77
    short1: 61 77 77 77
    short2: 61 62 77 77
    short3: 61 62 00 77
     long1: 61 77 77 77
     long2: 61 62 77 77
     long3: 61 62 63 77
     long4: 61 62 63 64
*/
char dest[4];
char src[10];

void dump_dest(const char *info) {
    printf("%10s:", info);
    for(int i = 0; i < 4; ++i) {
        printf(" %02x", dest[i]);
    }
    printf("\n");
}

int main() {
    memset(dest, 'w', sizeof(dest));
    dump_dest("w's");

    strcpy(src, "ab");  // src is shorter

    memset(dest, 'w', sizeof(dest));
    strncpy(dest, src, 1);
    dump_dest("short1");
  
    memset(dest, 'w', sizeof(dest));
    strncpy(dest, src, 2);
    dump_dest("short2");

    memset(dest, 'w', sizeof(dest));
    strncpy(dest, src, 3);
    dump_dest("short3");

    strcpy(src, "abcde");   // src is longer

    memset(dest, 'w', sizeof(dest));
    strncpy(dest, src, 1);
    dump_dest("long1");

    memset(dest, 'w', sizeof(dest));
    strncpy(dest, src, 2);
    dump_dest("long2");

    memset(dest, 'w', sizeof(dest));
    strncpy(dest, src, 3);
    dump_dest("long3");
  
    memset(dest, 'w', sizeof(dest));
    strncpy(dest, src, 4);
    dump_dest("long4");

    return 0;
}