Comparison between naive string concatenation and better one

gistfile1.c

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define SIZE 100000

int main() {
    int i;
    char *buffer;
    buffer = (char*) malloc(sizeof (char) * (SIZE + 1));
    clock_t t1, t2;

    // algorhythm1
    memset(buffer, 0, sizeof (buffer));
    t1 = clock();

    for (i = 0; i < SIZE; i++) {
        joinstring1(buffer, "a");
    }

    t2 = clock();
    printf("naive: %.3f\n", (double) (t2 - t1) / CLOCKS_PER_SEC);

    // algorhythm2
    memset(buffer, 0, sizeof (buffer));
    t1 = clock();

    int len = 0;
    for (i = 0; i < SIZE; i++) {
        len = joinstring2(buffer, "a", len);
    }

    t2 = clock();
    printf("modified: %.3f\n", (double) (t2 - t1) / CLOCKS_PER_SEC);

    free(buffer);
    return EXIT_SUCCESS;
}

joinstring1(char *dst, const char *src) {
    // forward to the tail of dst
    while (*(dst++) != '\0');
    dst--;

    // join
    while (*src != '\0') {
        *(dst++) = *(src++);
    }
}

int joinstring2(char *dst, const char *src, int dst_len) {
    // forward to the tail of dst
    dst += dst_len;

    // join
    int cnt = 0;
    while (*src != '\0') {
        *(dst++) = *(src++);
        cnt++;
    }

    return dst_len + cnt;
}

naive: 189.135
modified: 0.016