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- How do I use extern to share variables between source files?
First off, the extern keyword is not used for defining a variable; rather it is used for declaring a variable I can say extern is a storage class, not a data type extern is used to let other C files or external components know this variable is already defined somewhere Example: if you are building a library, no need to define global variable
- What is the effect of extern C in C++? - Stack Overflow
As far as I know, extern "C" also tells the compiler to use C calling conventions see also Exporting C++ classes from a DLL - Eli Bendersky's website (Google still finds it, but the site seems dead): extern "C" __declspec(dllexport) IKlass* __cdecl create_klass() Let's see what each part means, in order:
- variable declaration - When to use extern in C++ - Stack Overflow
The previous answers provided good explanations about extern But I want to add an important point You ask about extern in C++, not in C and I don't know why there is no answer mentioning the case when extern comes with const in C++ In C++, a const variable has internal linkage by default (not like C) So this scenario will lead to linking error:
- using extern template (C++11) to avoid instantiation
To prevent this, starting with C++0x, one could use the keyword extern in front of the class template specialization #include <MyClass> extern template class CMyClass<int>; The explicit instantion of the template class should happen only in a single translation unit, preferable the one with template definition (MyClass cpp)
- Why would you use extern C++? - Stack Overflow
If you have a class where some members have extern "C" linkage, you may wish the explicit state that the others are extern "C++" Note that the C++ Standard defines syntactically extern "anystring" It only give formal meanings to extern "C" and extern "C++" A compiler vendor is free to define extern "Pascal" or even extern "COM+" if they like
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