Accessing a global variable defined in a .cpp file in another .cpp file [duplicate]

问题

This question already has an answer here:

Access extern variable in C++ from another file (1 answer)

Closed 9 months ago.

Consider the following scenario:

MyFile.cpp:

const int myVar = 0; // global variable

AnotherFile.cpp:

void myFun()
{
    std::cout << myVar; // compiler error: Undefined symbol
}

Now if I add extern const int myVar; in AnotherFile.cpp before using, linker complains as

Unresolved external

I can move the declaration of myVar to MyFile.h and include MyFile.h in AnotherFile.cpp to solve the issue. But I do not want to move the declaration to the header file. Is there any other way I can make this work?

回答1:

In C++, const implies internal linkage. You need to declare myVar as extern in MyFile.cpp:

extern const int myVar = 0;

The in AnotherFile.cpp:

extern const int myVar;

来源：https://stackoverflow.com/questions/43798283/accessing-a-global-variable-defined-in-a-cpp-file-in-another-cpp-file