Static variable cannot be resolved [duplicate]

Question

In my VC++ 2008 project, I create two files, Globals.h and Globals.cpp, as follows:

Glboals.h:

#pragma once

extern ULONG g_ulMAPIUnicodeFlag;

Globals.cpp:

#include "StdAfx.h"
#include "Globals.h"
#include <mapidefs.h>

#ifdef _UNICODE

static ULONG g_ulMAPIUnicodeFlag = MAPI_UNICODE;

#else

static ULONG g_ulMAPIUnicodeFlag = 0;

#endif

Then I use the global variable in another file, TestGlboalDlg.cpp, as follows:

#include "Globals.h"

...

void CTestGlobalDlg::OnBnClickedButton1()
{
    // TODO: Add your control notification handler code here
    ULONG a;

    a = g_ulMAPIUnicodeFlag;
}

But get the following link error:

TestGlobalDlg.obj : error LNK2001: unresolved external symbol "unsigned long g_ulMAPIUnicodeFlag" (?g_ulMAPIUnicodeFlag@@3KA)

Why? If I remove the static modifier in GLobals.cpp, then everything is OK. However, static modifier is required since I need to set the value of the flag at the beginning of the program.

Thanks

static's purpose on a declaration at namespace scope is exactly to not make the declaration visible to other translation units. It does not mean the same as static on a declaration inside a class or at block scope. static is not required to initialize the variable at program startup. — walnut
– walnut, Commented Dec 18, 2019 at 2:51

robthebloke · Accepted Answer · 2019-12-18 03:14:00Z

2

static is the exact opposite of extern. Do not mix the two.

#ifdef _UNICODE

ULONG g_ulMAPIUnicodeFlag = MAPI_UNICODE;

#else

ULONG g_ulMAPIUnicodeFlag = 0;

#endif

answered Dec 18, 2019 at 3:14

robthebloke

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