Strcpy thru array subscribed

Question

In the Ritchie/Kernighan book, they show a few ways how to create a self made strcpy function, one of them is with using array subscribed instead of char pointers, but when I try this method and run the code it only gives me the second word in this case "world" and not the word "hello" any clue?

#include <stdio.h>

void xstrcpy(char *a, char *b)
{
    int i = 0;
    while((a[i] = b[i]) != '\0')
    {
        i++;
    }
}


int main()
{
    char name[20] = "hello";
    char names[20] = "world";
    xstrcpy(names, name);
    printf("%s\n", names);
}

Answer 1

Your function overwrites a with the content of b . You could call as like this:

xstrcpy(names + strlen(names), name);

Or you could implement concatenation. Require caller to pass in a sufficiently large string array ( dest ). Then find the end ( end ) of the string and copy src to dest . Using the pointers passed in, but you could also use separate indices into dest and src :

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

// require caller to pass in a dest array large enough for a copy of src
char *xstrcat(char *dest, const char *src) {
    char *end = strchr(dest, '\0');
    while(*end++ = *src++);
    return dest;
}

int main() {
    char dest[sizeof("hello") + sizeof("world") - 1] = "hello";
    char src[] = "world";
    xstrcat(dest, src);
    printf("%s\n", dest);
    return 0;
}