Printing an off_t

Question

I have a problem with my C code. It prints, but way too many characters. The code:

    #include<stdio.h>
    #include<inttypes.h>
    #include<unistd.h>
    #include<sys/types.h>
    #include<sys/stat.h>
    #include<unistd.h>
    #include<stdlib.h>
    struct stat buff;
    int main(int argc, char *argv[])
    {
      int p, i, fd[2], n;
      char message[10], *file, *no;
      pipe(fd);
      for(i = 1; i < = argc; i++)
      {p = fork();
       if ( p == 0 )
       {
         close ( fd[0] );
         if ( access( argv[i], F_OK ) != -1 )
            {printf( "%s is an existing file \n", argv[i] );
             fflush( stdout );

             stat( (const char*)argv[i] , &buff );
             printf( "%lld", (long long)buff.st_size );
             fflush( stdout );

             //sprintf( file , "%lld" , (long long)buff.st_size);
             //write( fd[1], file /*&buff->st_size*/ ,10 );
            }
         else if ( opendir ( argv[i] ) != NULL )
                {printf("%s is an existing directory \n", argv[i]);
                 fflush(stdout);
                }
                else
                  { srand( time(NULL));
                    n = rand()%11+5;
                    sprintf( no, "%d", n);
                    printf( "%s randomly number \n", no );
                    fflush( stdout );
                    write( fd[1], no /*sizeof((char*)(((int)'0')+n))*/, 10);
                  }
         close ( fd[1] );
         exit(0);
       }
      else
        if ( p == -1 )
            {
                printf( "error" );
                exit(1);
            }
        close( fd[1] );
        read ( fd[0] , message , 10 );
        printf ( "%s \n" , message );
        fflush ( stdout );
        close ( fd[0] );
        wait(0);
    }
   return 0;
}

This is the entire code. I know it is not very elegant, but I didn't find a better solution for printing the st_size. I tried to convert it to string but that didn't worked either. It won't read through pipe anything if the argument is a file. The output:

    449▒▒▒▒▒▒▒▒▒▒)▒▒▒▒▒t$1▒E▒D▒E▒D$▒▒$▒▒▒▒▒▒▒▒9▒rރ▒[^_]Ë$Ð▒U▒▒S▒▒▒E

Cannot reproduce (after adding the necessary headers, fixing `main` to return `int` and adding error checks). What compiler warnings do you get? You have the warnings turned on, don't you? — Fred Foo, May 03 '14 at 13:57
Is the code you show really the code the produces that output? That shouldn't be possible. And a small (unrelated) thing: You don't need to cast `argv[1]`, the compiler should handle it without warnings. — Some programmer dude, May 03 '14 at 14:00

score 1 · Accepted Answer · answered May 03 '14 at 15:29

1

You have this declaration:

char ,,,, *no;

And then you have this line:

sprintf( no, "%d", n);

Nowhere in the code do you allocate memory for no. This leads to undefined behavior as uninitialized local variables have indeterminate values, and you are writing out into seemingly random memory.

I don't know it this is the cause of your problem, but undefined behavior can cause all kind of weird symptoms.

You either need to use e.g. malloc to allocate memory for the variable, or make it an array (of ten characters, as that's what you write later).

answered May 03 '14 at 15:29

Some programmer dude

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Thank you very much. I`ve changed `char* no` into `char no[10]` and there are no more errors. – user3599200 May 03 '14 at 15:41
The new problem is that it reads only the first time from pipe. So if i got more than 1 argument the parent will keep printing the result for the first argument. – user3599200 May 03 '14 at 20:46

Printing an off_t

1 Answers1