C Exercises: Merge two files and write it in a new file

Last update on August 08 2025 12:52:54 (UTC/GMT +8 hours)

12. Merge Two Files

Write a program in C to merge two files and write them to another file.

Assume that the content of the file test.txt and test1.txr is :                                                                       
 The content of the file test.txt is  : 
This is the file test.txt. 

 The content of the file test1.txt is  : 
This is the file test1.txt.

Sample Solution:

C Code:

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

void main()
{
	FILE *fold1, *fold2, *fnew;
	char ch, fname1[20], fname2[20], fname3[30];

	printf("\n\n Merge two files and write it in a new file :\n");
	printf("-------------------------------------------------\n"); 	
	
	printf(" Input the 1st file name : ");
	scanf("%s",fname1);
	printf(" Input the 2nd file name : ");
	scanf("%s",fname2);
	printf(" Input the new file name where to merge the above two files : ");
	scanf("%s",fname3);
	fold1=fopen(fname1, "r");
	fold2=fopen(fname2, "r");
	if(fold1==NULL || fold2==NULL)
	{
//		perror("Error Message ");
		printf(" File does not exist or error in opening...!!\n");
		exit(EXIT_FAILURE);
	}
	fnew=fopen(fname3, "w");
	if(fnew==NULL)
	{
//		perror("Error Message ");
		printf(" File does not exist or error in opening...!!\n");
		exit(EXIT_FAILURE);
	}
	while((ch=fgetc(fold1))!=EOF)
	{
		fputc(ch, fnew);
	}
	while((ch=fgetc(fold2))!=EOF)
	{
		fputc(ch, fnew);
	}
	printf(" The two files merged into %s file successfully..!!\n\n", fname3);
	fclose(fold1);
	fclose(fold2);
	fclose(fnew);
}

Sample Output:

 Merge two files and write it in a new file :                                                                 
-------------------------------------------------                                                             
 Input the 1st file name : test.txt                                                                           
 Input the 2nd file name : test1.txt                                                                          
 Input the new file name where to merge the above two files : mergefiles.txt                                  
 The two files merged into mergefiles.txt file successfully..!!

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to merge two files by alternating lines from each file into a new file.
Write a C program to merge two files and sort the combined content alphabetically before writing to a new file.
Write a C program to merge two files and remove duplicate lines during the merge process.
Write a C program to merge multiple files into one, preserving the order and adding file separators between contents.

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