Chastity’s Hex Compare Tool

Welcome to Chastity’s Hex Compare program also known as “chastecmp”. Enter two filenames as command line arguments such as:

./chastecmp file1.txt file2.txt

It works for any binary files too, not just text. In fact for text comparison you want entirely different tools. This tool can be used to find the tiny differences between files in hexadecimal. It shows only those bytes which are different. I wrote it as a solution to a reddit user who asked how to compare two files in hexadecimal.

It is an improvement over the Linux “cmp” tool which displays the offsets in decimal and the bytes in octal. Aside from using two different bases in the data, it falls short of usefulness because there are more hex editors than octal editors.

Here are also some graphical tools I can recommend if you are looking for a GUI instead of my command line program.

vbindiff
wxHexeditor

Below is the full source code:

#include <stdio.h>
#include <stdlib.h>
 
int main(int argc, char *argv[])
{
 int argx,x;
 FILE* fp[3]; /*file pointers*/
 int c1,c2;
 long flength[3]; /*length of the file opened*/
   
 /*printf("argc=%i\n",argc);*/

 if(argc<3)
 {
  printf("Welcome to Chastity's Hex Compare program also known as \"chastecmp\".\n\n");
  printf("Enter two filenames as command line arguments such as:\n");
  printf("%s file1.txt file2.txt\n",argv[0]);
  return 0;
 }

 argx=1;
 while(argx<3)
 {
   fp[argx] = fopen(argv[argx], "rb"); /*Try to open the file.*/
   if(!fp[argx]) /*If the pointer is NULL then this becomes true and the file open has failed!*/
   {
    printf("Error: Cannot open file \"%s\": ",argv[argx]);
    printf("No such file or directory\n");
    return 1;
   }
  /*printf("File \"%s\": opened.\n",argv[argx]);*/

  printf("fp[%X] = fopen(%s, \"rb\");\n",argx,argv[argx]);
  argx++;
 }

 printf("Comparing files %s and %s\n",argv[1],argv[2]);

 argx=1;
 while(argx<3)
 {
  fseek(fp[argx],0,SEEK_END); /*go to end of file*/
  flength[argx]=ftell(fp[argx]); /*get position of the file*/
  printf("length of file fp[%X]=%lX\n",argx,flength[argx]);
  fseek(fp[argx],0,SEEK_SET); /*go back to the beginning*/
  argx++;
 }

 x=0;
 while(x<flength[1])
 {
  c1 = fgetc(fp[1]);
  c2 = fgetc(fp[2]);
  if(c1!=c2)
  {
   printf("%08X: %02X %02X\n",x,c1,c2);
  }
  x++;  
 }

 argx=1;
 while(argx<3)
 {
  fclose(fp[argx]);
  printf("fclose(fp[%X]);\n",argx);
  argx++;
 }

 return 0;
}