In C programming using standard library functions, what does a typical file copy program do when copying data from one file to another?

Introduction / Context:
A classic beginner level C programming exercise is to write a program that copies the contents of one file to another. This tests understanding of file I or O functions such as fopen, fclose, fgetc, fputc, fread, and fwrite, as well as error checking and loops.

Given Data / Assumptions:

• There is a source file whose contents we want to duplicate.
• We want to create or overwrite a destination file with exactly the same bytes.
• We are using the standard C library file I or O mechanisms.

Concept / Approach:
The usual file copy program opens the source file in read mode and the destination file in write (or binary write) mode. It then loops, reading characters or fixed size blocks from the source and immediately writing them to the destination. The process continues until a read function indicates end of file. At the end, both files are closed. This approach preserves the original data exactly and is independent of the file type, because the program does not interpret the content, it only transfers bytes.

Step-by-Step Solution:
Step 1: Call fopen on the source file with mode such as "rb" or "r". Check for a null pointer to detect failure.Step 2: Call fopen on the destination file with mode such as "wb" or "w". Again check for failure.Step 3: Use a loop to read data. For text you can use fgetc and fputc, or for binary data you can use fread and fwrite on a buffer.Step 4: Continue reading and writing until the read function signals end of file or an error.Step 5: Close both files with fclose to flush buffers and release resources.

Verification / Alternative check:
If you implement this logic and then compare the original and copied files using a tool such as a checksum or a diff program, they should match exactly. This confirms that the program correctly copied all data.

Why Other Options Are Wrong:
Option B describes creating a hard link or symbolic link, which is done by operating system utilities or system calls, not by a simple byte copying C program.Option C limits itself to the first line and duplicates it, which is not a true file copy.Option D mentions copying only metadata, which again is not the purpose of the usual file copy task.

Common Pitfalls:
Common mistakes in C include forgetting to check return values from fopen, failing to close files, or using the wrong modes (for example using text mode on binary files on some systems). Another issue is using fgets and fputs in a way that does not copy all characters, such as missing end-of-line characters.

Final Answer:
The correct behaviour is It opens the source file for reading and the destination file for writing, repeatedly reads data from the source, and writes the same data to the destination until end-of-file is reached.