Re: generic strncpy - off-by-one error

[Albert Cahalan]

You're all wrong. This is some kind of programming
test for sure!

Let us imagine that glibc has a correct version.
By exhaustive testing, I found a version that works.
Here it is, along with the test code:

//////////////////////////////////////////////////////
#define _GNU_SOURCE
#include <string.h>
#include <stdlib.h>
#include <stdio.h>

// first correct implementation!
char * strncpy_good(char *dest, const char *src, size_t count){
  char *tmp = dest;
  memset(dest,'\0',count);
  while (count-- && (*tmp++ = *src++))
    ;
  return dest;
}

static char ref[32];
static char hmm[32];

static char s0[] = "";
static char s1[] = "1";
static char s2[] = "12";
static char s6[] = "123456";
static char s7[] = "1234567";
static char s8[] = "12345678";
static char s9[] = "123456789";

static void tester(const char *src, size_t count){
  memset(ref,'%',sizeof ref);
  memset(hmm,'%',sizeof hmm);
  strncpy     (ref+2,src,count);
  strncpy_good(hmm+2,src,count);
  if(memcmp(ref,hmm,sizeof hmm)){
    printf("error @ size %d\n",(int)count);
  }
}  
   
int main(int argc, char *argv[]){
  int i = 15;
  while(i--){
    tester(s0,i);
    tester(s1,i);
    tester(s2,i);
    tester(s6,i);
    tester(s7,i);
    tester(s8,i);
    tester(s9,i);
  }
  return 0;
}
////////////////////////////////////////////////////////////


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/