[Freeciv-Dev] patch: zstrncpy() (PR#112)

[David Pfitzner <dwp@xxxxxxxxxxxxxx>]

This patch adds and uses a new function zstrncpy:

/******************************************************************
 * zstrncpy():
 *
 * Like strncpy(), but with some features to make it easier to
 * keep strings null-terminated.  In particular, always writes
 * a terminating null, including when input is longer than n.
 *
 * Eg, often see code like:
 *    strncpy(dest, src, sizeof(dest));
 *    dest[sizeof(dest)-1] = '\0';
 * or sometimes just:
 *    strncpy(dest, src, sizeof(dest)-1);
 * if one can be sure dest[] is initially filled with nulls.
 * With zstrncpy can now omit second line, without needing above
 * contraint, and just do:
 *    zstrncpy(dest, src, sizeof(dest));
 *
 * Also, zstrncpy() does not pad dest with nulls if src is
 * shorter than n (doing so could be inefficient if n is large
 * and src happens to be short).
 *
 * Also, return value is different from strncpy: zstrncpy returns
 * the number of chars written, not including the trailing null.
 * (This is intended to help keep track when cat-ing to a buffer.)
 *
 * It is an error to call this with (n <= 0), or with
 * either dest or src NULL.
 *
 * Yes, n should probably be size_t, but int is enough for me.
 *****************************************************************/
int zstrncpy(char *dest, const char *src, int n)
{
  assert(dest);
  assert(src);
  assert(n>0);
  {
    char * const start = dest;
    char * const final = dest + n - 1;

    while( (dest <= final) && ((*dest++ = *src++)) )
      ;

    *--dest = '\0';
    
    return dest - start;
  }
}

(Actually, as I post this it now occurs to me that it may be 
more useful to just return 0 if (n<=0), for case when cat-ing 
to a buffer and decrementing the space remaining.)

Regards,
-- David

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