Copy a Text File in C

Algorithm

1. Read the source and the target file names.
2. Open the source for reading and the target for writing, checking both results.
3. Read one character at a time with fgetc and write it with fputc until EOF.
4. Close both files and report success.

This program opens real files on the machine that runs it. The online Run button uses a remote sandbox without your local files, so the sample shows the error path for a missing file. To see the copy succeed, save the code locally, create a text file with some lines, and run the program with that file name.

C program

#include <stdio.h>

int main(void) {
    char source_name[100], target_name[100];
    FILE *source, *target;
    int ch;

    printf("Enter source file name:\n");
    scanf("%99s", source_name);
    printf("Enter target file name:\n");
    scanf("%99s", target_name);

    source = fopen(source_name, "r");
    if (source == NULL) {
        printf("Error: cannot open source file %s\n", source_name);
        return 1;
    }

    target = fopen(target_name, "w");
    if (target == NULL) {
        printf("Error: cannot create target file %s\n", target_name);
        fclose(source);
        return 1;
    }

    while ((ch = fgetc(source)) != EOF) {
        fputc(ch, target);
    }

    fclose(source);
    fclose(target);
    printf("Copied %s to %s\n", source_name, target_name);
    return 0;
}

Sample input and output

missing.txt
copy.txt

Enter source file name:
Enter target file name:
Error: cannot open source file missing.txt

How the program works

fopen returns NULL when a file cannot be opened, so the program checks the result before it reads or writes anything. Each opened file is closed on every exit path so that no handle is left open.

fgetc returns an int, not a char, because EOF is a negative value that a char might not be able to hold on some platforms. Storing the result in an int keeps the end-of-file test reliable.

Viva questions

Common mistakes

• Using a char to hold the result of fgetc, which can break the EOF check.
• Forgetting to check fopen for NULL and then reading from a null pointer.
• Opening the target in "r" mode instead of "w", so it cannot be written.
• On Windows, text mode converts each newline to CR+LF when writing, so a copy can differ byte-for-byte from the source. Use "rb" and "wb" when an exact byte copy is needed.