diff on c-source file always returns "files differ" - UNIX for Dummies Questions & Answers

C-Prog-Man · #1 (**permalink**) 08-30-2006

I have a c-source file that is evidently seen by unix as a binary file. When doing a diff between it and older versions with substantial differences, diff will only return "files differ".

I have tried cat-ing the file to another file; tried using the "-h" on the diff; I have tried ftp-ing it back and forth as ascii; I have played with chmod; I have tried using dos2unix... no matter what I do I can't get Unix to see the file as a text file.

Anybody seen this before... and have a solution?

Corona688 · #2 (**permalink**) 08-30-2006

Sounds like you've got gremlins. You can use some commands illustrated in that thread to strip out the offending characters.

It's not UNIX that's being stubborn about this, just diff. UNIX has no concept of "text file", everything's just data.

Note that, if it can't diff, it probably can't compile either. Most compilers throw up on high ASCII.

Which file have you been doing all the pounding on? Maybye you're fixing the wrong one, and the gremlin's in the other?

C-Prog-Man · #3 (**permalink**) 08-30-2006

I've changed this file quite often and all the versions of it seem to compile without a problem. No visible gremlins......

nathan · #4 (**permalink**) 08-30-2006

What does 'file' say? Also, you could write a small C program to filter any 'gremlin' characters, visible or not.

Code:

$ file Clean.c
Clean.c: ASCII C program text

$ cat Clean.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
main( int argc, char *argv[] )
{
  char c;

  while( (read( STDIN_FILENO , &c , sizeof( char ) )) > 0 )
    if (isprint( c )||isspace(c))
      printf("%c",c);

  return 0;
}

C-Prog-Man · #5 (**permalink**) 08-31-2006

$ file main.c
main.c: ascii text

I'll look into the invisible garbage.

C-Prog-Man · #6 (**permalink**) 08-31-2006

Quote:

Originally Posted by nathan

What does 'file' say? Also, you could write a small C program to filter any 'gremlin' characters, visible or not.

Code:

$ file Clean.c
Clean.c: ASCII C program text

$ cat Clean.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
main( int argc, char *argv[] )
{
  char c;

  while( (read( STDIN_FILENO , &c , sizeof( char ) )) > 0 )
    if (isprint( c )||isspace(c))
      printf("%c",c);

  return 0;
}

I used the following code to wash the problem file. The input file size was 25093, the output file size is 25093.... but the result is now "diff" sees it as text and not binary.

Thanks for your help.....

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

main()
{
FILE *fpInput, *fdOutput;
char c;

fdOutput = fopen("mainout.c", "w");

fpInput = fopen("main.c", "r");
while (fread(&c, sizeof(char), 1, fpInput) > 0)
{
if(isprint(c) || isspace(c))
fprintf(fdOutput,"%c", c);
}
fclose (fpInput);
fclose (fdOutput);
}

Corona688 · #7 (**permalink**) 08-31-2006

Glad the problem is solved. That they're the same length is very odd -- the only way that program can change the file is by excluding bytes! Thus I have found an exception to what I previously thought was a rule, that UNIX does not differentiate between text and binary files. What UNIX are you using?

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