C++ || File Copier Using Memory Mapped Files

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The following is another homework assignment which was presented in an Operating Systems Concepts class. Using commandline arguments, the following is a program which implements a file copier using memory mapped files. This program makes use of the “mmap” function call provided on Unix based systems.


How To Use Memory Mapped Files
How To Get The Size Of A File
How To Create A File Of Any Size

==== 1. OVERVIEW ====

A memory mapped file is a segment of virtual memory which has been assigned a direct byte for byte correlation with some portion of a file or file like resource. The primary benefit of memory mapping a file is increasing I/O performance, especially when used on large files. Accessing memory mapped files is faster than using direct read and write operations. Memory mapped files are designed to simplify and optimize file access.

The program demonstrated on this page works with any file type (i.e: txt, cpp, jpg, png, mp4, flv, etc.) and copies the contents of one file, and saves it into another separate output file.


This program has the following flow of control:

1. The program is invoked with the source file name and the destination file name as commandline arguments.
2. The program uses the mmap() system call to map both files into memory.
3. The program uses the memory-mapped file memory to to copy the source file to the destination file.

This program is also modified in such a way that you cannot do an mmap on the same file. For example, if you have an input file “A” as the source file, the destination file “B” needs to have a different filename. If both the source and the destination files have the same filename, an error message is displayed, and the program exits. In order for this program to work, the source and the destination files must have different names.

The highlighted lines are sections of interest to look out for.

The code is heavily commented, so no further insight is necessary. If you have any questions, feel free to leave a comment below.

The following is sample output:

./mcp 1.png 2.png

The source file "1.png" is 42004 bytes

The destination file "2.png" has been created and is 42004 bytes

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