Created: 2008-12-25 21:33
Updated: 2018-12-25 11:02



mapped_file allows you to create a simple read-only file mapping in an object-oriented cross-platform way. It may be used to read small files completely in memory without the performance penalty of read syscalls.


mapped_file is designed to be as minimal as possible and thus easy to use and to extend. The following example shows this by loading a shader into OpenGL.

GLuint shader = glCreateShader(GL_FRAGMENT_SHADER);
try {
	mapped_file map("shader.frag"); // maps "shader.frag" into memory
	// an exception is thrown if the file cannot be opened
} catch (mapped_file::io_exception e) {
	std::cout << e.what() << std::endl;
// map.length() gets the length in bytes of the mapped file
// *map returns a char pointer to the mapped data
glShaderSource(shader, map.length(), *map, NULL);
// the file is automatically unmapped if map goes out of scope

If you don't want to use exceptions compile with -fno-exceptions. mapped_file will then call exit(1) if an error occurs. MSVC Users: You have to define __EXCEPTIONS if you want exceptions.

Supported Operating Systems

At the time of this writing the following OS were supported:

  • Windows 95 and higher through MapViewOfFile
  • POSIX through mmap
  • Other OS through malloc and fread

Note: The malloc backend does not use memory-mapped files and is therefore substantially slower and may need more memory.

How do I add mapped_file to my project?

Just copy mappedfile.c and mappedfile.h to your source tree.


Copyright (C) 2008-2009 Benjamin Kramer

This software is provided 'as-is', without any express or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software.

Permission is granted to anyone to use this software for any purpose, including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
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