Strange Segfault in windows

exvor · 07-24-2007, 07:43 PM

I am having a rather strange issue. I keep getting a segfault in windows when I attempt to run the first program but if I remove the if and else statements it works properly. Also they both compile without any errors given.

Anyone have any ideas why ?

Program with if and else

Code:

 
#include<stdio.h> 
#include<dirent.h> 
#include<time.h> 
#include<sys/stat.h>
#include<sys/types.h> 



int main (int argc , char *argv[]) 
{ 
    DIR *curdir = NULL; 
    struct dirent *dname = NULL; 
    struct stat *fstat; 
    struct tm *ftime; 

    int fcount = 0; 
    int dircount = 0;
    unsigned int totalfsize = 0; 
    unsigned int fsize; 
    time_t *ptime = NULL; 
    
     
        if (argc == 1) 
       {
         curdir = opendir("."); 
         printf("\nOpening .\n");
       } 
    else 
         {
           curdir = opendir(argv[1]); 
           printf("\nOpening %s\n",argv[1]); 
         } 
 
  
    

    while ((dname = readdir(curdir))) 
       { 
         

            
 
         stat(dname->d_name,fstat); 
               
         if((S_ISDIR(fstat->st_mode)))
            {
             fsize = (unsigned int)fstat->st_size; 
               ptime = &fstat->st_mtime;
                 
               ftime = localtime(ptime); 
               printf("\n%02i:%02i on %i/%i/%-8i",ftime->tm_hour,ftime->tm_min,(ftime->tm_mon + 

1),ftime->tm_mday,(ftime->tm_year + 1900)); 
               printf("%-22s%s","<DIR>",dname->d_name); 
               dircount++; 
            }
         else 
            {
               
               fsize = (unsigned int)fstat->st_size; 
               ptime = &fstat->st_mtime;
                 
               ftime = localtime(ptime); 
               printf("\n%02i:%02i on %i/%i/%i",ftime->tm_hour,ftime->tm_min,(ftime->tm_mon + 

1),ftime->tm_mday,(ftime->tm_year + 1900)); 
               printf("%19u bytes %s",fsize,dname->d_name);
               totalfsize = totalfsize + fsize; 
               fcount++;
               
            }
        }

    closedir(curdir); 

   
   printf("\nThere are %i files %i directorys found.\n",fcount,dircount); 
   printf("Size of files: %i\n",totalfsize); 
  
   
   return 0; 
}

Program without if and else

Code:

 
#include<stdio.h> 
#include<dirent.h> 
#include<time.h> 
#include<sys/stat.h>
#include<sys/types.h> 



int main (int argc , char *argv[]) 
{ 
    DIR *curdir = NULL; 
    struct dirent *dname = NULL; 
    struct stat *fstat; 
    struct tm *ftime; 

    int fcount = 0; 
    int dircount = 0;
    unsigned int totalfsize = 0; 
    unsigned int fsize; 
    time_t *ptime = NULL; 
    
     
        
   curdir = opendir("."); 
    

    while ((dname = readdir(curdir))) 
       { 
         

            
 
         stat(dname->d_name,fstat); 
               
         if((S_ISDIR(fstat->st_mode)))
            {
             fsize = (unsigned int)fstat->st_size; 
               ptime = &fstat->st_mtime;
                 
               ftime = localtime(ptime); 
               printf("\n%02i:%02i on %i/%i/%-8i",ftime->tm_hour,ftime->tm_min,(ftime->tm_mon + 

1),ftime->tm_mday,(ftime->tm_year + 1900)); 
               printf("%-22s%s","<DIR>",dname->d_name); 
               dircount++; 
            }
         else 
            {
               
               fsize = (unsigned int)fstat->st_size; 
               ptime = &fstat->st_mtime;
                 
               ftime = localtime(ptime); 
               printf("\n%02i:%02i on %i/%i/%i",ftime->tm_hour,ftime->tm_min,(ftime->tm_mon + 

1),ftime->tm_mday,(ftime->tm_year + 1900)); 
               printf("%19u bytes %s",fsize,dname->d_name);
               totalfsize = totalfsize + fsize; 
               fcount++;
               
            }
        }

    closedir(curdir); 

   
   printf("\nThere are %i files %i directorys found.\n",fcount,dircount); 
   printf("Size of files: %i\n",totalfsize); 
  
   
   return 0; 
}

rocket357 · 07-24-2007, 08:07 PM

Compiling with Visual C++? Running the first one with/without args? If you're running with args, what args?

exvor · 07-24-2007, 08:47 PM

Being compiled using mingw and it fails with or without arguments.

only argument you could give it is a path.

Sorry I didn't specify the language but this is C

rocket357 · 07-24-2007, 09:32 PM

I realize it's C =)

I'll look at it...let me get mingw installed...heh

Edit - Umm...hrmmm...

I downloaded/installed mingw (the mingw-runtime, gcc-core, binutils, and w32api packages...all from CURRENT), then compiled both sets of source you've listed above. Both compiled without error, and both ran without error...additionally, the first one ran fine with or without args (and I double checked the output for accuracy). Do you have an outdated/broken mingw install? What options are you passing to gcc.exe? (I compiled as such: "bin\gcc.exe -o WithIfElse.exe WithIfElse.c" and "bin\gcc.exe -o WithoutIfElse.exe WithoutIfElse.c")

exvor · 07-25-2007, 05:21 PM

I have narrowed it down it seams to sprintf being called before calling stat. If I do a sprintf before I call stat then the program crashes but if I just do a printf or anything else it works properly
so it seams like it has something to do with the interaction of sprintf and stat ??

very strange.

paulsm4 · 07-25-2007, 05:35 PM

Try this:

Code:

int main (int argc , char *argv[]) 
{ 
    DIR *curdir = NULL; 
    struct dirent *dname = NULL; 
    struct tm *ftime = NULL; 
    struct stat fstat; 
...

'Hope that helps .. PSM

exvor · 07-25-2007, 05:52 PM

Yeah but if I do that then i get compile errors about invalid assignment.

exvor · 07-25-2007, 06:18 PM

Never mind I see what the issue is. The memory for that location is being overwritten by another process. Its actually just fortunate that it even works at all. This is correct for readdir tho as far as i can tell from the manpage

this seams to have something to do with reentrant and non reentrant versions of each function. One takes the structure to place the data as the other just returns a pointer to a structure created in the function. How is this memory freed and is this common for functions defined in sys ?

Quote:

The pointer returned by readdir() points to data which may be overwritten by another call to readdir() on the same directory stream. This data is not overwritten by another call to readdir() on a different directory stream.

paulsm4 · 07-25-2007, 08:19 PM

Try this:

Code:

#include <stdio.h>
#include <errno.h>
#include <dirent.h>
#include <sys/stat.h>
#include <sys/types.h>

int
main (int argc , char *argv[])
{
  DIR *curdir = NULL;
  struct dirent *dname = NULL;
  struct stat fstat;

  /* Open directory */
  curdir = opendir(".");
  if (curdir == NULL)
  {
    perror ("opendir failed");
    return 1;
  }

  /* List directories */
  while ( (dname = readdir (curdir)) != NULL )
  {
    if (stat (dname->d_name, &fstat) < 0)
    {
      printf ("stat (%s) failed, errno: %d",
        dname->d_name, errno);
      continue;
    }
    if (S_ISDIR (fstat.st_mode))
      printf ("DIR: %s, st_mode: 0x%x, st_mtime: 0x%x\n",
        dname->d_name, (unsigned)fstat.st_mode, (unsigned)fstat.st_mtime);
    else
      printf ("file: %s, st_mode: 0x%x, st_mtime: 0x%x\n",
        dname->d_name, (unsigned)fstat.st_mode, (unsigned)fstat.st_mtime);
  }

  /* Close DIR */
  closedir (curdir);
  printf ("Done.\n");
  return 0;
}