#define SAFE_STRNCPY_ZERO_FILL 

#include <assert.h>
#include <errno.h>
/* safe_srncpy() is Copyright 1998 by Mark Whitis <whitis@dbd.com> */
/* All Rights reserved. */
/* use it or distribute it (including for profit) at your own risk */
/* but please don't GPL it.  Retain this notice.  Modified versions */
/* should be clearly labeled as such. */
char *safe_strncpy(char *dst, char *src, int size)
{
   char *savedst;

   savedst = dst;

   /* Make sure destination buffer exists and has positive size */
   #ifdef SAFE_STRNCPY_DESTINATION_REQUIRED
      assert(dst);
      assert(size>0);
   #else
      if(!dst) { 
         errno = EINVAL;
         return(savedst); 
      }
      if(size<1) { 
         errno = EINVAL;
         return(NULL); 
      }
   #endif

   /* Do something sensible if we receive a NULL pointer */
   #ifdef SAFE_STRNCPY_ABORT_NOSRC
      assert(src);
   #else
      /* treat NULL and "", identically */
      if(!src) {
         dst[0]=0;
         #ifdef SAFE_STRNCPY_ERROR_NOSRC
            errno = EINVAL;
         #endif
         return(savedst);
      }
   #endif

   size--;  /* leave room for trailing zero */
   while(*src && ( size-- > 0 ) ) {
      #ifdef SAFE_STRNCPY_MOVING_ZERO_TERM
         *(dst+1) = 0;
      #endif
      *dst++ = *src++;
   }
   *dst = 0;

   #ifdef SAFE_STRNCPY_ZERO_FILL
      while( size-- > 0 ) {
         *dst++ = 0;
      }
   #endif

   /* If we didn't copy the whole string, report error */
   if(*src) {
      errno=ENOSPC;
      #ifdef SAFE_STRNCPY_ALL_OR_NOTHING
         /* return zero length string instead of truncated string */
         /* on truncation error */
         *savedst = 0;         
      #endif
   }
   #ifdef SAFE_STRNCPY_TRUNC_ABORT
      assert(!*src);
   #endif

   return(savedst);
}         


main()
{
   char buf[4096];
   char sample[]="This is a test.  This is only a test";
   safe_strncpy(buf,sample,sizeof(buf));
   printf("buf=%s\n",buf);

   buf[25]=0x7A;
   safe_strncpy(buf,sample,25);
   printf("buf=%s\n",buf);
   assert(buf[25]=0x7A);

   buf[75]=0x7A;
   safe_strncpy(buf,sample,sizeof(buf));
   printf("buf=%s\n",buf);
   assert(buf[75]!=0x7A);
}