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Can I mix extern and const, as extern const? If yes, does the const qualifier impose it's reign only within the scope it's declared in or should it exactly match the declaration of the translational unit it's declared in? I.e. can I declare say extern const int i; even when the actual i is not a const and vice versa?
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Yes, you can use them together. If you declare "extern const int i", then i is const over its full scope. It is impossible to redefine it as non-const.
In a const variable declaration, it specifies that the variable has external linkage. The extern must be applied to all declarations in all files. (Global const variables have internal linkage by default.) extern "C" specifies that the function is defined elsewhere and uses the C-language calling convention.
The “extern” keyword is used to declare and define the external variables. The keyword [ extern “C” ] is used to declare functions in C++ which is implemented and compiled in C language. It uses C libraries in C++ language.
extern "C" void foo(); This means the function foo will be linked using the C conventions for linkage (maybe because this is a function defined in a C library or is a function intended to be called by C programs).
The usual pattern is:
extern const int a_global_var; #include "file.h" const int a_global_var = /* some const expression */; Edit: Incorporated legends2k's comment. Thanks.
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