C Language: what does the .mm extension stand for?
Objective CObjective C++Objective C Problem Overview
A project with some Objective-C has a few C classes with the implementation files having a .mm extension.
file.h
file.mm
What does the .mm mean? Shouldn't it just be .m?
Objective C Solutions
Solution 1 - Objective C
The extension .mm is the extension for the C++ compilation unit expected by the Objective-C compiler, while the .m extension is the extension for the C compilation unit expected by the Objective-C compiler.
That's assuming you don't use a compiler flag to override the file extension, as this gentleman has done.
Solution 2 - Objective C
Objective C++, mixes C++ and Objective C. http://en.wikipedia.org/wiki/Objective-C#Objective-C.2B.2B
Solution 3 - Objective C
.mm files are like .cpp files to the Objective-C compiler. They activate the C++ compiler instead of the C compiler.
The following question on performance has additional useful information:
https://stackoverflow.com/questions/2317868/objective-c-m-mm-performance-difference