Copy a File

CSC-115 · Semester I · C Programming

intermediate25 minAvailable

Cin-browser interpreter · runs locally

#include <stdio.h>
#include <string.h>

int main() {
  char source[64] = "hello world";
  char dest[64] = "";
  strcpy(dest, source);
  printf("Copied: %s\n", dest);
  return 0;
}

11 lines

Output

Write some code, then press Run. Stdout and errors appear here.

Lab brief

Objective

Open a source file, copy its contents character by character to a destination file, and verify the result.

Theory & concepts

Copying a file is a read-write loop: pull one character with fgetc and push it with fputc until EOF. Two fopen calls open the source for reading and the destination for writing; the loop transfers data between them; fclose closes both.

Rendering diagram…

Character-by-character file copy loop

FILE *src = fopen("in.txt", "r");
FILE *dst = fopen("out.txt", "w");
int ch;

while ((ch = fgetc(src)) != EOF)
    fputc(ch, dst);

Check both handles before the loop

If src is NULL the loop crashes on the first fgetc; if dst is NULL every fputc writes to nothing. Open both, verify both with an if (f == NULL) error check, then start the copy loop.

Prerequisites

Lesson: Opening and closing files
Lesson: Character file I/O

Instructions

1Open in.txt for reading and copy.txt for writing.
2Check both fopen calls for NULL and print an error if either fails.
3Loop with fgetc until EOF, writing each character to the destination.
4Close both files.
5Create a sample in.txt, run the program, and compare copy.txt with in.txt.

Tasks

Copy the file
After running, copy.txt must contain exactly the text of in.txt.
Verify byte-for-byte
Compare the two files and confirm they are identical, including line breaks.
Handle a missing source
Run with in.txt absent and confirm a clear error message instead of a crash.
Copy without overwriting
Change the destination mode to "a" and observe how repeated runs append instead of overwrite.

Self-check

The destination file matches the source exactly.
Both files are closed with fclose after use.
A missing source file is reported cleanly.
The student can explain the EOF loop condition.

Environment

editorstdout consolefile systemtest cases

Copy a File · C Programming · Learn CSIT