linux prog problem

afreedboy · 06-26-2004, 09:24 AM

Code:

#include<stdio.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<unistd.h>
#include<errno.h>
#include<string.h>
#include<fcntl.h>
int main(int argc, char *argv[])
{        //  argv[1]="abc.txt";
        if(argc!=2)
        {
                printf("Usage ./a.out <filename> \n");
                return -1;
        }
        char filename[20];
        strcpy(filename, argv[1]);
        int fd;
        fd=open(filename,O_RDONLY);
        if(fd<0)
        {
        printf("error open file");
        return -1;
        }
        int b=lseek(fd,0,SEEK_SET);
        if(b!=0)
        {printf("internal file error");
        return -1;
        }

        char *c;
        int d=1;
        while(d!=0)
        {
        int i=0;
        d=read(fd,c,22);
        if(d==-1)
        {printf("file error");int errno;printf("%s",errno);return -1;}
        if(d!=0)
        while(d>i)
        {

        printf("%c",c[i]);
        i++;
        }
        }
        close(fd);
        return 0;
}

That is my program that I write with Turbo C. And then I run that program in my SuSe 9. That works absolutely fine except I need to change some #include files. That is not a problem. But when I connect to Unix server by using secure CRT and run on it. It gave me error from I got by errno:Segmentation fault

I am so confused now

**Salem** · 06-26-2004, 09:40 AM

> char *c;
Which 22 bytes is this pointing at?

Try
char c[22];

Oh, and are you writing this in C or C++
Because it's a lot like neither at the moment.

afreedboy · 06-26-2004, 09:55 AM

Quote:

Originally Posted by Salem

> char *c;
Which 22 bytes is this pointing at?

hey I change it to char *c and now it is working.
when i type something like " ./a.out abc.txt "

it print out all text from abc.txt, but still print segmentation fault.

i already turn off errno lines.

by the way, i intend this program as a C program

**Salem** · 06-26-2004, 10:02 AM

It needs to be a char array!
Or you call malloc - your choice

Post your latest code

afreedboy · 06-26-2004, 10:09 AM

Quote:

Originally Posted by Salem

It needs to be a char array!
Or you call malloc - your choice

Post your latest code

Code:

#include<stdio.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<unistd.h>
//#include<errno.h>
#include<string.h>
#include<fcntl.h>
int main(int argc, char *argv[])
{        //  argv[1]="abc.txt";
        if(argc!=2)
        {
                printf("Usage ./a.out <filename> \n");
                return -1;
        }
        char *filename;
        strcpy(filename, argv[1]);
        int fd;
        fd=open(filename,O_RDONLY);
        if(fd<0)
        {
        printf("error open file");
        return -1;
        }
        int b=lseek(fd,0,SEEK_SET);
        if(b!=0)
        {printf("internal file error");
        return -1;
        }

        char c[2];
        int d=1;
        while(d!=0)
        {
        int i=0;
        d=read(fd,c,1);
        if(d==-1)
        {
        printf("file error");
//      int errno;
//      printf("%s",errno);
        return -1;
        }
        if(d!=0)
        while(d>i)
        {

        printf("%c",c[i]);
        i++;
        }
        }
        close(fd);
        return 0;
}

that is my latest code and here is output:

Code:

$ ./a.out abcd.txt
1234567
Segmentation fault

in abcd.txt i already put 1234567, so i want only 1234567. i don't know where Segmentation fault come from though.

afreedboy · 06-26-2004, 10:22 AM

i also tried debugging using gdb. here is what i got:

Code:

(gdb) step
43              if(d!=0)
(gdb) step
32              while(d!=0)
(gdb) step
51              close(fd);
(gdb) step
52              return 0;
(gdb) step
53      }
(gdb) step
0x42015574 in __libc_start_main () from /lib/tls/libc.so.6
(gdb) step
Single stepping until exit from function __libc_start_main, 
which has no line number information.

Program received signal SIGSEGV, Segmentation fault.
0x4000c6a0 in _dl_fini () from /lib/ld-linux.so.2
(gdb)

i don't know which part of my program transmit SIGSEGV

**Thantos** · 06-26-2004, 10:44 AM

Quote:

by the way, i intend this program as a C program

This is most definatly NOT a C program. Also fix your indentation

I ran it fine. Made a few changes but nothing major:

Code:

#include<stdio.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<unistd.h>
#include<string.h>
#include<fcntl.h>

int main(int argc, char *argv[])
{
        if(argc!=2)
        {
                printf("Usage ./a.out <filename> \n");
                return -1;
        }

        int fd;
        fd=open(argv[1],O_RDONLY);
        if(fd<0)
        {
          printf("error open file");
          return -1;
        }
        // This part really isn't needed as it will already be pointed at the beginning
        int b=lseek(fd,0,SEEK_SET);
        if(b!=0)
        {
          printf("internal file error");
          return -1;
        }

        char c[2];
        int d=1;
        while(d!=0)
        {
          int i=0;
          d=read(fd,c,sizeof c);
          if(d==-1)
          {
            printf("file error");
            return -1;
          }
          if(d!=0)
            while(d>i)
            {
              printf("%c",c[i]);
              i++;
            }
        }

        close(fd);
        return 0;
}

afreedboy · 06-28-2004, 12:13 AM

Mr. Thantos,

you just changed sizeof c right?

That still don't work. I mean I can run but still show segmentation fault.

**Thantos** · 06-28-2004, 12:21 AM

looking at the gdb log you posted it appears the fault is happening after main() terminates.

Are you using gcc or g++? If so which version?

afreedboy · 06-28-2004, 02:19 AM

I am using gcc. Problem comes from main or gcc?

**Salem** · 06-28-2004, 06:31 AM

Post your actual latest code - I've no idea whether you are running some modification of your code, or that provided by Thantos

**Thantos** · 06-28-2004, 06:44 AM

well there could be a problem since the code is not C. Try it with g++ and see what happens.

afreedboy · 06-30-2004, 08:31 AM

Code:

#include<sys/stat.h>
#include<unistd.h>
//#include<string.h>
#include<fcntl.h>

int main(int argc, char *argv[])
{

        int fd;
        char c;
        int d=1;
        int i=0;

        if(argc!=2)
        {
                printf("Usage ./a.out <filename> \n");
                return -1;
        }

        fd=open(argv[1],O_RDONLY);
        if(fd<0)
        {
          printf("error open file");
          return -1;
        }

        while(d!=0)
        {
          d=read(fd,&c,1);
          if(d==-1)
          {
                printf("file error");
                return -1;
          }
          printf("%c",c);
        }
        close(fd);
        return 0;
}

One of my friend rewrite like above and that is working fine on that Unix server. But I can't find any clues why his server is refusing first code.

06-26-2004, 09:40 AM	#2
Salem and the hat of Jobseeking Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,636	> char *c; Which 22 bytes is this pointing at? Try char c[22]; Oh, and are you writing this in C or C++ Because it's a lot like neither at the moment. __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
Salem is offline

06-26-2004, 10:02 AM	#4
Salem and the hat of Jobseeking Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,636	It needs to be a char array! Or you call malloc - your choice Post your latest code __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
Salem is offline

06-28-2004, 12:13 AM	#8
afreedboy Microsoft Lover Join Date: Nov 2003 Posts: 189	Mr. Thantos, you just changed sizeof c right? That still don't work. I mean I can run but still show segmentation fault.
afreedboy is offline

06-28-2004, 12:21 AM	#9
Thantos & the hat of GPL slaying Join Date: Sep 2001 Posts: 5,732	looking at the gdb log you posted it appears the fault is happening after main() terminates. Are you using gcc or g++? If so which version?
Thantos is offline

06-28-2004, 02:19 AM	#10
afreedboy Microsoft Lover Join Date: Nov 2003 Posts: 189	I am using gcc. Problem comes from main or gcc?
afreedboy is offline

06-28-2004, 06:31 AM	#11
Salem and the hat of Jobseeking Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,636	Post your actual latest code - I've no idea whether you are running some modification of your code, or that provided by Thantos __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
Salem is offline

06-28-2004, 06:44 AM	#12
Thantos & the hat of GPL slaying Join Date: Sep 2001 Posts: 5,732	well there could be a problem since the code is not C. Try it with g++ and see what happens.
Thantos is offline

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