Segmentation fault when free

[Nash Nipples]

--- On Fri, 9/19/08, Unga <unga888 at yahoo.com> wrote:

> From: Unga <unga888 at yahoo.com>
> Subject: Segmentation fault when free
> To: freebsd-questions at freebsd.org
> Date: Friday, September 19, 2008, 9:17 AM
> Hi all
> 
> I'm running FreeBSD 7 on i386. I have a C program
> compiled with gcc 4.2.1 20070719.
> 
> Logically my program is:
> 
> char *a;
> char *b;
> char *c;
> 
> while (cond)
> {
>  a = f1(); /* malloc() and send a string */
>  b = f2(); /* malloc() and send a string */
> 
>  c = (char *) malloc(strlen(a) + strlen(b) + 1);
>  c[0] = '\0';
> 
>  strcat(c, a);
>  strcat(c, b);
> 
>  free(a);
>  free(b);
> }
> 
> When it executes free(b), my program exits with
> Segmentation fault: 11. The free(a) executes well.
> 
> The problem is with free(b). Even swap free(b) first and
> free(a) next, it still crashes at free(b).
> 
> If I comment out free() lines, further down the program,
> first few characters of one string get dropped when executes
> a completely unrelated line.
> 
> How could I bit more narrow down the problem? 
> 
> Many thanks in advance.
> 
> Kind regards
> Unga
> 
> 

im affraid i didnt implement your request correctly but the program below did not crash my server under root in 60 seconds

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char *a;
char *b;
char *c;

char *abd = "Hi, im a string 1\0";
char *bbd = "Hey, im a string 2\0";

char *f1(void){
  char *ab;
  ab = malloc(strlen (abd));
  memcpy(ab, abd, strlen(abd));
  printf("f1(): %s\n", ab);
  return ab;
}

char *f2(void){
  char *bb;
  bb = malloc(strlen (bbd));
  memcpy(bb, bbd, strlen(bbd));
  printf("f1(): %s\n", bb);
  return bb;
}

int
main(void)
{

while (1)
{

a = f1(); /* malloc() and send a string */
b = f2(); /* malloc() and send a string */

c = (char *) malloc(strlen(a) + strlen(b) + 1);
c[0] = '\0';

strcat(c, a);
strcat(c, b);

free(a);
free(b);
}
}