CODEWITHSUNDEEP
c++objective-cios
user773578
user773578

Reputation: 1161

cpp compilation issues in iOS project

I have added some objective C files and c++ files to an existing iOS project. When I import a .h file of a .mm file into a .h file with a corresponding .m file I get all kinds of errors.

When I change the .m file of the .h file importing the new code to .mm I then get the same previous errors but with new errors regarding the new .mm file.

Im not really sure how to fix this.

I am using ARC if this has any effect.

It complains about namespace (unknown type), also Unknown name issues with an imported .mm file, expected expression error on a statement containing :: in a .h file of a .mm file. What I dont get is that these files work correctly in the project I copied them over from. I only took the source from the project. And have added header search paths to the directory. I also selected create references to the added directories option.

For some reason the files arent in the compile source section, and when I try to add them, the file selector tree doesnt contain these source files I added. The added directory is also blue instead of yellow, but empty.

Upvotes: 1

Views: 818

Answers (1)

Matt Wilding
Matt Wilding

Reputation: 20153

As you know, C++ code can only be used from .mm files. When the compiler complains about namespace being an unknown type, it typically means that the Objective C compiler is being used when the Objective C++ compiler should be used. More simply: you have a .m file that needs to be a .mm.

Speaking generally, there are two options you can pursue. Every time an Objective C file complains, change it to a .mm. This is a slippery slope, and generally results in your entire project cascading into a giant ball of Objective C++. The other option is to quarantine the C++, so that only a bare minimum of your Objective C files need the .mm extension.

Obviously, the latter is the better choice. The likely cause of the confusion is #importing a header file that contains C++ code from elsewhere in your app that doesn't actually require C++. If the C++ is an implementation detail of an Objective C class, you can try to keep the C++ out of the class' header file by leveraging Class Extensions. Otherwise, you can create an Objective C class whose only purpose is to wrap the C++ in its own implementation, while exposing a clean header file for other classes to consume.

Basically, If you can keep your headers clean, then you won't have to worry about accidentally indirectly #importing some C++ into an unsuspecting compilation unit.

Upvotes: 3

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