gcc is at once a compiler for C, Objective-C, and C++. You can intermix C++ and Objective-C code to some degree. To instruct the compiler that a file contains C++ code as well as Objective-C, use the file extension .mm or .M instead of .m.
Following are some ways in which C++ and Objective-C code can be used together:
Objective-C objects can have fields that point to C++ objects, and vice versa.
Objective-C code can call methods on C++ objects, and vice versa.
Objective-C objects can have C++ objects (as opposed to pointers) as fields, but only if the C++ class has no virtual methods.
However, Objective-C and C++ are not completely compatible. Here are some things you can’t do:
Objective-C classes can’t inherit from C++ classes, and vice versa.
You can’t declare Objective-C classes in C++ namespaces or templates, or vice versa.
You can’t use C++ keywords for Objective-C variable names.
You can’t call Objective-C methods with C++ syntax, or vice versa.
Finally, there are some restrictions that are imposed to avoid ambiguity:
You can’t use the name id
as a C++ template name. If you could, the declaration id<
TypeName
>
var
could be either a C++ template
declaration or an Objective-C declaration using a protocol.
If you are passing a globally-scoped C++ variable to an Objective-C method, you need a space between the first and second colons. For example:
[obj
methodName
: ::aGlobal
].
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