Make *.mm files compilable on all platforms

m_andrej

Hello,

I have a Qt application for iOS that uses some Objective-C snippets in an Objective-C++ file (*.mm extension). Now I need to make the code compile on other platforms. I have wrapped all Objective-C lines in #ifdef Q_OS_IOS blocks, so I need to convince qmake to compile *.mm files as C++. Any idea how to do that?

I tried the following in my *.pro file:

HEADERS += \
    ...
    src/CServerCommunicator.h 

ios {
    OBJECTIVE_SOURCES += src/CServerCommunicator.mm
}

!ios {
    SOURCES += src/CServerCommunicator.mm
}

It does seem to compile the *.mm file as C++, but only as C++98. It's showing compile errors for things like nullptr.

mrjj

Hi
on windows, I have to put
CONFIG +=C++11
in my pro file when using mingw to get new c++ so to speak.

m_andrej

I already have the line CONFIG += C++11.

But I managed to solve this by adding QMAKE_EXT_CPP += .mm. At least on Windows this compiles fine:

HEADERS += \
    ...
    src/CServerCommunicator.h 

ios {
    OBJECTIVE_SOURCES += src/CServerCommunicator.mm
}

!ios {
    QMAKE_EXT_CPP += .mm
    SOURCES += src/CServerCommunicator.mm
}

mrjj

ah super.

SGaist

Hi,

Out of curiosity, why not keep the iOS specific code in the *mm file and implement the standard c++ part in a cpp file ?

m_andrej

Because

I don't know how to do it
I don't see how it's better from my current solution ;-)

SGaist

HEADERS += \
    ...
    src/CServerCommunicator.h 

ios {
    OBJECTIVE_SOURCES += src/CServerCommunicator.mm
} else {
    SOURCES += src/CServerCommunicator.cpp
}

It's better in the sense that you clearly separate building code for platform that support Objective-C++ from the others. It also makes your code easier to read and maintain for you and your team mates.

Just as an example, would you go read an Objective-C++ file if you build a library on Windows ?

m_andrej

It seems an interesting idea. But most of my *.mm file contains C++ code which is used also on iOS. Having two files (mm and cpp) would mean having duplicate C++ code in both.

SGaist

Nothing forbids you to have a common file for code that is the same and two specialized files, one for iOS and one for the other platforms.