ex27.c

#undef NDEBUG
#include "dbg.h"
#include <stdio.h>
#include <assert.h>

/* Naive copy assuming all inputs are always valid
*taken from K&R C and cleaned up a bit
*/
void copy(char to[], char from[])
{
    int i = 0;

    //while loop will not end if from isn't '\0' terminated
    while((to[i] = from [i]) != '\0') {
        i++;
    }
}

/* A safer version that checks for many common errors using length
*of each string to control loops and termination
*/
int safercopy(int from_len, char *from, int to_len, char *to)
{
    assert(from != NULL && to != NULL && "from and to can't be NULL");
    int i = 0;
    int max = from_len > to_len - 1 ? to_len - 1 : from_len;

    //to_len must have at least 1 byte
    if(from_len < 0 || to_len <= 0) return -1;

    for(i = 0; i < max; i++0 {
        to[i] = from[i];
    }

    to[to_len - 1] = '\0';

    return i;
}

int main(int argc, char *argv[])
{
    // careful to understand why we can get these sizes
    char from[] = "0123456789";
    int from_len = sizeof(from);

    //notice that it's 7 chars + \0
    char to[] = "0123456";
    int to_len = sizeof(to);

    debug("Copying '%s':%d to '%s':%d", from, from_len, to, to_len);

    int rc = safercopy(from_len, from, to_len, to);
    check(rc > 0, "Failed to safercopy.:");
    check(to[to_len - 1] == '\0', "String not terminated.");

    debug("Result is: '%s':%d", to, to_len);

    //not try to break it
    rc = safercopy(from_len * -1, from, to_len, to);
    check(rc == -1, "safercopy should fail #1");
    check(to[to_len - 1] == '\0', "String not terminated,");

    rc = safercopy(from_len, from, 0, to);
    check(rc == -1, "safercopy should fail #2");
    check(to[to_len - 1] == '\0', "String not terminated.");

    return 0;

error:
    return 1;
}