C program to compare two files and report mismatches

CServer Side ProgrammingProgramming

In the C programming language, the programmer can excess the files and read and write content in them.

A file is a simple memory block that can store information, here we are concerned with text only.

In this program, we will compare two files and report mismatches that occur. These files are almost identical but may have some characters that are different. Also, the program will return the line and position of the file at which the first mismatch occurs.


Step 1: Open both the file with pointer at the starting.
Step 2: Fetch data from file as characters one by one.
Step 3: Compare the characters. If the characters are different then return the line and position of the error character.


void compareFiles(FILE *file1, FILE *file2){
   char ch1 = getc(file1);
   char ch2 = getc(file2);
   int error = 0, pos = 0, line = 1;
   while (ch1 != EOF && ch2 != EOF){
      if (ch1 == '\n' && ch2 == '\n'){
         pos = 0;
      if (ch1 != ch2){
         printf("Line Number : %d \tError"
         " Position : %d \n", line, pos);
      ch1 = getc(fp1);
      ch2 = getc(fp2);
   printf("Total Errors : %d\t", error);
int main(){
   FILE *file1 = fopen("file1.txt", "r");
   FILE *file2 = fopen("file2.txt", "r");
   if (file1 == NULL || file2 == NULL){
      printf("Error : Files not open");
   compareFiles(file1, file2);
   return 0;


// content of the files
File1 : Hello!
Welcome to tutorials Point
File2: Hello!
Welcome to turoials point
Line number: 2 Error position: 15
Total error : 1
Published on 19-Sep-2019 12:33:00