Copying the contents of one file to another in C involves reading data from the source file and writing it to the destination file. This process is useful for file management tasks, such as creating backups or duplicating data.

Program: Copy Contents of One File to Another in C

Here’s a simple program that demonstrates how to copy the contents from one file to another.

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

int main() {
    FILE *sourceFile, *destFile;
    char ch;

    // Open the source file in read mode
    sourceFile = fopen("source.txt", "r");
    if (sourceFile == NULL) {
        perror("Error opening source file");
        return EXIT_FAILURE;
    }

    // Open the destination file in write mode
    destFile = fopen("destination.txt", "w");
    if (destFile == NULL) {
        perror("Error opening destination file");
        fclose(sourceFile); // Close the source file before exiting
        return EXIT_FAILURE;
    }

    // Copy contents from source file to destination file
    while ((ch = fgetc(sourceFile)) != EOF) {
        fputc(ch, destFile); // Write the character to the destination file
    }

    printf("Contents copied successfully from source.txt to destination.txt\n");

    // Close both files
    fclose(sourceFile);
    fclose(destFile);

    return EXIT_SUCCESS;
}

Explanation of the Program

1. Header Files:

   • #include <stdio.h>: Includes standard I/O functions for file handling.
   • #include <stdlib.h>: Provides definitions for exit status and error handling.

2. File Pointers:

   • FILE *sourceFile, *destFile;: Declares pointers to handle the source and destination files.

3. Open Source File:

   • Opening:

     sourceFile = fopen("source.txt", "r");
     

     This line attempts to open source.txt in read mode.
   • Error Checking:

     if (sourceFile == NULL) {
         perror("Error opening source file");
         return EXIT_FAILURE;
     }
     

     If the file can't be opened (e.g., it doesn't exist), an error message is displayed and the program exits.

4. Open Destination File:

   • Opening:

     destFile = fopen("destination.txt", "w");
     

     This opens (or creates) destination.txt in write mode.
   • Error Checking: Similar to the source file, it checks for errors when opening the destination file.

5. Copying Process:

   • The program uses a loop to read characters from the source file one at a time:

     while ((ch = fgetc(sourceFile)) != EOF) {
         fputc(ch, destFile);
     }
     

     • fgetc(sourceFile) reads a single character from sourceFile.
     • The loop continues until the end of the file (EOF) is reached.
     • fputc(ch, destFile) writes the read character to destFile.

6. Closing Files:

   • After copying is complete, both files are closed:

     fclose(sourceFile);
     fclose(destFile);
     

   • This ensures that all resources are properly released.

7. Program Output:

   • After the successful completion of the file copy operation, a message is printed:

     printf("Contents copied successfully from source.txt to destination.txt\n");
     

How to Run the Program

1. Create the Source File: First, create a text file named source.txt in the same directory as the program and add some text to it.

2. Compile the Code: Use a C compiler like gcc to compile the code:

   gcc copy_file.c -o copy_file
   

3. Execute the Program: Run the compiled program:

   ./copy_file
   

Example Output

Assuming source.txt contains the following text:

Hello, World!
This is a test file.

After running the program, the output will be:

Contents copied successfully from source.txt to destination.txt

The contents of destination.txt will now be:

Hello, World!
This is a test file.

Conclusion

This program illustrates the basic file handling operations in C: opening files, reading from a source file, writing to a destination file, and closing the files afterward. Understanding how to work with files is a foundational skill in C programming, enabling you to manage data effectively and efficiently. This method can be expanded for more complex file operations, such as error logging, binary file copying, or even merging multiple files.