Accessing a global variable defined in a .cpp file in another .cpp file

Question

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?

score 6 · Accepted Answer · edited May 23 '17 at 12:34

6

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;

edited May 23 '17 at 12:34

Community

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answered May 05 '17 at 07:05

themiurge

1,619
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No, just keep compiling and linking as before. – themiurge May 05 '17 at 07:13
Could you please post the command you use? – themiurge May 05 '17 at 07:15
Oh sorry I thought you already declared it in AnotherFile.cpp. You need to put this in AnotherFile.cpp: `extern const int myVar;` – themiurge May 05 '17 at 07:18

Accessing a global variable defined in a .cpp file in another .cpp file

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