将可变参数模板参数包传递给下一个函数

Question

I have done my own reimplementation of printf() (classic) in my debugging code.

    template<typename T, typename ...Args>
    void Printf(wchar_t const * message, T value, Args ...args);
    void Printf(wchar_t const * message);
    void Printf();

It uses variadic templates and works perfectly fine.

Now I want to use Printf() in couple of functions that are going to accept almost same arguments but perform Printf() in different ways. Here is one of the client functions for Printf()

template<typename ...Args>
void Debug::Line(unsigned int in_tabs, wchar_t const * in_string, Args...in_args){
    for (unsigned int i = 0; i < in_tabs; ++i)
        Tab();
    Printf(in_string, in_args...);
    NewLine();
}

As soon I start using this construct, I start getting UNRESOLVED linker errors

error LNK2019: unresolved external symbol "public: static void __cdecl Nerv::Debug::Line<>(unsigned int,wchar_t *)" (??$Line@$$$V@Debug@Nerv@@SAXIPA_W@Z) referenced in function "public: void __thiscall Nerv::UI::NervUIRect::DebugRect(void)" (?DebugRect@NervUIRect@UI@Nerv@@QAEXXZ)
error LNK2019: unresolved external symbol "public: static void __cdecl Nerv::Debug::Line<int,int>(unsigned int,wchar_t *,int,int)" (??$Line@HH@Debug@Nerv@@SAXIPA_WHH@Z) referenced in function "public: void __thiscall Nerv::UI::NervUIRect::DebugRect(void)" (?DebugRect@NervUIRect@UI@Nerv@@QAEXXZ)

It's strange to me, cause I've tested this construct on a simpler case first and it worked fine.

template<typename T,typename...Ts>
void Printf(T value,Ts...args){
    OutputDebugString(value);
    Printf(args...);
}
void Printf(){

}

template<typename...Args>
void UsePrintf(Args...args){
    Printf(args...);
}

The difference from the simple case is that all theese functions (that don't work) are static members of a Debug class and that there are some additional function arguments. So how am I supposed to deal with this?

Answer 1

正如TartanLlama指出的那样，模板函数体需要在头文件中可用/通过将定义和声明置于头部中或者通过在头部末尾包含带有函数实现的cpp文件来实现