My C Program Crashed the Terminal :(

As part of my homework assignment (due tonight!), I have to write two versions of the standard library function strncpy(), one using array's and one using pointers.

The strncpy() function basically takes two arguments, *src and *dest, and copies n number of bytes from *src to *dest.

#include 

// Function declarations
char *mystrncpy(char *dest, const char *src, size_t n);

main()
{
    char a[] = "this is a string";
    char b[50];

    mystrncpy(b, a, 400); // here is the problem
    printf("%sn", b);

    return 0;
}

// My attempt to replicate the strncpy() function with pointers
char *mystrncpy(char *dest, const char *src, size_t n)
{
    int i = 0;
    while (i <= n) {
        *dest = *src;
        src++;
        dest++;
        i++;
    }
}

While testing this pointer version of the function, I passed a much larger size (400) to the function than had been allocated for the destination variable (b[50]).

eris:hw3 raam$ gcc problem8.c -o problem8
eris:hw3 raam$ ./problem8
this is a string
Segmentation fault

There is no better way to tell me my function needs more work than to stick a big "Application quit unexpectedly" message in my face! (And thankfully, my entire iTerm app did not crash.)

I wrote a post a few weeks ago about how eerily close C variables are to the machine, and the way this program crashed further confirms that point. I can't imagine the kinds of nasty things I will be able to do once I learn more advanced C functions. 😀