krx70600.c

answer of the c programming language second edition

/******************************************************
   KnR 7-6
   --------
   Write a program to compare two files and print the
   first line where they differ.

   Author: Rick Dearman
   email: [e-mail]

   Note: This program prints ALL the lines that are 
         different using the <> indicators used by
	 the unix diff command. However this program
	 will not cope with something as simple as a
	 line being removed.
	 
	 In reality the program would be more useful
	 if it searched forward for matching lines. 
	 This would be a better indicator of the simple
	 removal of some lines.
	 
	 This has lead me to track down a version of the 
	 "diff" command available on GNU/Linux systems.
	 for more information go to the web site at:
	 www.gnu.org

******************************************************/
#include <stdio.h>
#include <string.h>
#define MAXLINE 1000

void diff_line( char *lineone, char *linetwo, int linenumber )
{
  if(strcmp (lineone, linetwo) < 0 || strcmp (lineone, linetwo) > 0)
    printf( "%d<%s\n%d>%s\n", linenumber, lineone, linenumber, linetwo);
}

int main(int argc, char *argv[] )
{
  FILE *fp1, *fp2;
  char fp1_line[MAXLINE], fp2_line[MAXLINE];
  int i;

  if ( argc != 3 )
    {
      printf("differ fileone filetwo\n");
      exit(0);
    }

  fp1 = fopen( argv[1], "r" );
  if ( ! fp1 )
    {
      printf("Error opening file %s\n", argv[1]);
    }

  fp2 = fopen( argv[2], "r" );
  if ( ! fp2 )
    {
      printf("Error opening file %s\n", argv[2]);
    }
  i = 0;
  while ( (fgets(fp1_line, MAXLINE, fp1) != NULL) 
	  && (fgets(fp2_line, MAXLINE, fp2) != NULL))
  {
    diff_line( fp1_line, fp2_line, i );
    i++;
  }

  return 0;
}