[SOLVED] problem with fopen() "rb" param

atlantis43 · 11-22-2013, 07:06 PM

Wondering if there is any reason why my clang compiler is unable to open a file "myFile.txt" with the parameter
"rb". The file is in the same directory as my code, so I don't know what else could be wrong. Code is written in "C", and comes from a text.

dwhitney67 · 11-22-2013, 07:10 PM

Quote:

Originally Posted by atlantis43

Wondering if there is any reason why my clang compiler is unable to open a file "myFile.txt" with the parameter
"rb". The file is in the same directory as my code, so I don't know what else could be wrong. Code is written in "C", and comes from a text.

Perhaps it is "clang"? Why not use a proven compiler such as GCC (err, 'gcc' for C source code)?

ntubski · 11-22-2013, 07:24 PM

Quote:

Originally Posted by atlantis43

The file is in the same directory as my code, so I don't know what else could be wrong.

The directory where the code lives doesn't matter, what matters is what directory you are in when calling the executable.

When you say "unable to open" does that mean fopen() returns NULL? Did you check errno (use perror(3) to translate the number to a message)?

atlantis43 · 11-22-2013, 07:48 PM

Yes, returning NULL, although the file does have text within. I further realized that there must be something all fouled, since I cant even open it in "r" or "a" params.
I'll have to check it further to see if there's something more obvious that's the cause of my problem.

dwhitney67 · 11-22-2013, 07:54 PM

Quote:

Originally Posted by atlantis43

Yes, returning NULL, although the file does have text within. I further realized that there must be something all fouled, since I cant even open it in "r" or "a" params.
I'll have to check it further to see if there's something more obvious that's the cause of my problem.

Hey-sus!!! Do you have the appropriate permissions to open the file? This is Linux right, not windows?

atlantis43 · 11-22-2013, 08:15 PM

Quote:

Hey-sus!!! Do you have the appropriate permissions to open the file? This is Linux right, not windows?

Yup, Linux.
No problems with any other File I/O code examples, so I haven't figured out what's wrong yet. Also tried gcc,as suggested earlier, but no benefit. Must be something wrong with my 'clear buffer' code.
Code is as follows, so perhaps someone can relieve my confusion.

Code:

/* reverse.c -- displays a file in reverse order */
#include <stdio.h>
#include <stdlib.h>
#define CNTL_Z '\032'   /* eof marker in DOS text files */
#define SLEN 50
int main(void)
{
    char file[SLEN];
    char ch;
    FILE *fp;
    long count, last;

    puts("Enter the name of the file to be processed:");
    fgets(file,50,stdin);
    while (fgets(file,50,stdin) != NULL && file[0] != '\n')
    {
if ((fp = fopen(file,"rb")) == NULL)
    {                      /* read-only and binary modes */
        printf("reverse can't open %s\n", file);
        exit(1);
    }
    }
    fseek(fp, 0L, SEEK_END);        /* go to end of file */
    last = ftell(fp);
/* if SEEK_END not supported, use this instead           */
/*  last = 0;
    while (getc(fp) != EOF)
        last++;
*/
    for (count = last- 1; count >= 0; count--)
    {
        fseek(fp, count, SEEK_SET); /* go backward       */
        ch = getc(fp);
    /* for DOS, works with UNIX */
        if (ch != CNTL_Z && ch != '\r')
            putchar(ch);
    /* for Macintosh            */
    /*  if (ch == '\r')
            putchar('\n');
         else
             putchar(ch)
    */
   }
   putchar('\n');
   fclose(fp);
   
   return 0;
}

atlantis43 · 11-22-2013, 09:15 PM

Quote:

Perhaps it is "clang"? Why not use a proven compiler such as GCC (err, 'gcc' for C source code)?

Just found that you were correct: it does compile with gcc (all error handling excluded) if I leave the code as original, which used gets(), which I tried to convert to fgets(). Clearly a problem with my code for clearing '\n'from buffer.

rknichols · 11-22-2013, 11:09 PM

Quote:

Originally Posted by atlantis43

Code:

if ((fp = fopen(file,"rb")) == NULL)
    {                      /* read-only and binary modes */
        printf("reverse can't open %s\n", file);
        exit(1);
    }
    }

Replace that printf() with

Code:

        perror(file);

so that you get to see what actually failed.

NevemTeve · 11-23-2013, 12:27 AM

Compilers don't open files (except for source/object files), libc does which is compiler-independent. Fix your program.

Code:

if (! fgets (buff, sizeof (buff), stdin)) {
    /* read error */
}
len= strlen (buff);
if (len>0 && buff[len-1]=='\n') buff[--len]= '\0';

dwhitney67 · 11-23-2013, 06:19 AM

Or just:

Code:

if (! fgets (buff, sizeof (buff), stdin)) {
    /* read error */
}
char* nl = strchr(buff, '\n');
if (nl)
{
    *nl = '\0';
}