Implementation of c stdlib functions strlen, strcpy & strcpy

str.c

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

size_t _strlen(const char *s)
{
    size_t size = 0;
    while (*s++)
        ++size;
    return size;
}

void _strcat(char *to, const char *from) {
    while (*to)
        to++;
    while (*to++ = *from++);
}

void _strcpy(char *dest, const char *src) {
    while (*dest++ = *src++);
}

int main() {
    char test_string[11] = "hello ";
    char test_concat[] = "world";
    _strcat(test_string, test_concat);
    int len = _strlen(test_string);
 
    char *buffer = malloc(len + sizeof "");
    _strcpy(buffer, test_string);
 
    printf("%s is %d chars long.\n", buffer, len);
    return 0;
}