LNK2019 when define UNICODE/_UNICODE - windows

Question

I am using TCHAR and I get the error when I define UNICODE / _UNICODE. Here is my code.
function.h
#define UNICODE
#define _UNICODE
#include <tchar.h>
#include <windows.h>
BOOL bLogging(LPCTSTR szContent, ...);
function.cpp
#include "function.h"
BOOL bLogging(LPCTSTR szContent, ...)
{
body of function
}
plugin.cpp
#include "function.h"
bool pluginInit(PLUG_INITSTRUCT* initStruct)
{
bLogging(TEXT("hello, world!"));
}
The above code makes the error
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
LNK2019 unresolved external symbol "int __cdecl bLogging(char const *,...)" (?bLogging##YAHPBDZZ) referenced in function "bool __cdecl pluginInit(struct PLUG_INITSTRUCT *)" (?pluginInit##YA_NPAUPLUG_INITSTRUCT###Z)
But without the UNICODE / _UNICODE, it builds as ASCII characters, it works well.
========== Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped ==========

Answer 1

Raymond's comment is probably the correct answer. Otherwise, your code looks fine.
Unless you are trying to have backwards compatibility support for Windows 95, you don't need TCHAR macros. Simpler to just avoid this stuff and use either const wchar_t* or LPCWSTR as your string type.
Adjusting your code as an example:
function.h
#pragma once
#include <windows.h>
BOOL bLogging(const wchar_t* szContent, ...);
function.cpp
#include "function.h"
BOOL bLogging(const wchar_t* szContent, ...)
{
body of function
}
plugin.cpp
#include "function.h"
bool pluginInit(PLUG_INITSTRUCT* initStruct)
{
bLogging(L"Hello World");
}