Question

I have these two simple files that define a C++ class with a tryME function

______myclass.h________________
#pragma once

void tryME()
{

}

class myclass
{
public:
    myclass(void);
    myclass(void);


    void callTryME();
};

_________myclass.cpp____________

#include "myclass.h"


myclass::myclass(void)
{
}


myclass::~myclass(void)
{
}

void myclass::callTryME()
{
    tryME();
}

This gives the error

1>myclass.obj : error LNK2005: “void __cdecl TryME(void)”
(?TryME@@YAXXZ) already defined in tryout.obj 1>C:\tryout.exe : fatal
error LNK1169: one or more multiply defined symbols found

If I declare the tryME() function as static, the problem is solved. But why?

I know that the .h file is included in the .cpp file and then compiled (into a translation unit) and that static variables and functions are visible to the entire translation unit they’re contained into, but why doesn’t the program work without the “static” keyword? The function tryME should be “global” outside the class and thus visible, isn’t that correct? Does the calling put a “this->” before the tryME() ?

Answer 1

This:

inline void tryME()
{

}

Otherwise, you’re breaking the one definition rule.

Defining a non-inline method in a header file will result in it being exported by all translation units that include that header, ergo the error.