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C program to compare contents of two files

By IncludeHelp Last updated : March 10, 2024

Comparing two files in C refers to reading and comparing the content of the character of the files by characters. In this tutorial, we will learn how can we compare the content of two files using the C program.

Steps to compare contents of two files in C

• Open both of the files in read mode using the fopen() function.
• Read the content of the files using the loop.
• Compare the characters one by one, if any of the characters do not match break the loop.
• Print the results.
• Close the files using the fclose() function.

C program to compare two files

Below is the C program to compare two files:

//Write a program to compare two file.
#include <stdio.h>
#include <string.h>
 
int main(int argc, char *argv[])
{
    FILE *fp1   ;
    FILE *fp2   ;
     
    int cnt1 = 0;
    int cnt2 = 0;
    int flg  = 0;
     
    if( argc < 3 )
    {
        printf("Insufficient Arguments!!!\n");
        printf("Please use \"program-name file-name1 file-name2\" format.\n");
        return -1;
    }
     
    fp1 = fopen(argv[1],"r");
    if( fp1 == NULL )
    {
        printf("\n%s File can not be opened : \n",argv[1]);
        return -1;
    }
     
    // move file pointer to end and get total number of bytes
    fseek(fp1,0,SEEK_END);
    cnt1 = ftell(fp1);
     
    fp2 = fopen(argv[2],"r");
    if( fp2 == NULL )
    {
        printf("\n%s File can not be opened : \n",argv[2]);
        return -1;
    }
     
    // move file pointer to end and get total number of bytes
    fseek(fp2,0,SEEK_END);
    cnt2 = ftell(fp2);
     
    fseek(fp1,0,SEEK_SET);
    fseek(fp2,0,SEEK_SET);
     
    // check for the total number of bytes
    if( cnt1 != cnt2 ){
        printf("\nFile contents are not same\n");
    }
    else
    {
        while( ! feof(fp1) )
        {
                if( fgetc(fp1) != fgetc(fp2) )
                {
                    flg = 1;
                    break;
                }
        }
         
        if( flg )   printf("\nFile contents are not same.\n");
        else        printf("\nFile contents are same.\n");
    }
 
    fclose(fp1);
    fclose(fp2);
 
    return 0;
}

Output

Terminal command: ./compPrg file1.txt file2.txt
File contents are not same.

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