Strnpcpy.c

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#include <sys/types.h>
#include <string.h>
#include "Strn.h"
 
/*
 * Copy src to dst, truncating or null-padding to always copy n-1 bytes.
 *
 * This routine differs from strncpy in that it returns a pointer to the end
 * of the buffer, instead of strncat which returns a pointer to the start.
 */
char *
Strnpcpy(char *const dst, const char *const src, size_t n)
{
    register char *d;
    register const char *s;
    register char c;
    char *ret;
    register size_t i;
 
    d = dst;
    if (n != 0) {
        s = src;
        /* If they specified a maximum of n characters, use n - 1 chars to
         * hold the copy, and the last character in the array as a NUL.
         * This is the difference between the regular strncpy routine.
         * strncpy doesn't guarantee that your new string will have a
         * NUL terminator, but this routine does.
         */
        for (i=1; i<n; i++) {
            c = *s++;
            if (c == '\0') {
                ret = d;    /* Return ptr to end byte. */
                *d++ = c;
#if (STRNP_ZERO_PAD == 1)
                /* Pad with zeros. */
                for (; i<n; i++)
                    *d++ = 0;
#endif  /* STRNP_ZERO_PAD */
                return ret;
            }
            *d++ = c;
        }
        /* If we get here, then we have a full string, with n - 1 characters,
         * so now we NUL terminate it and go home.
         */
        *d = '\0';
        return (d); /* Return ptr to end byte. */
    } else {
        *d = 0;
    }
    return (d); /* Return ptr to end byte. */
}   /* Strnpcpy */
 
/* eof Strn.c */