C Language: what does the .mm extension stand for?

Question

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?

http://philjordan.eu/article/strategies-for-using-c++-in-objective-c-projects — Darius Miliauskas, Apr 14 '15 at 19:42

Edwin Buck · Accepted Answer · 2012-04-26T14:27:02.060

85

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.

edited Apr 26 '12 at 14:27

answered Apr 26 '12 at 14:19

Edwin Buck

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score 29 · Answer 2 · answered Apr 26 '12 at 14:17

29

Objective C++, mixes C++ and Objective C. http://en.wikipedia.org/wiki/Objective-C#Objective-C.2B.2B

answered Apr 26 '12 at 14:17

djechlin

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score 20 · Answer 3 · edited May 23 '17 at 11:54

20

.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:

Objective-C, .m / .mm performance difference?

edited May 23 '17 at 11:54

Community

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answered Apr 26 '12 at 14:16

Almo

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C Language: what does the .mm extension stand for?

3 Answers3

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