Question

考虑下面的C ++程序，它用VC ++编译但无法用g ++编译

D:\temp>cat test.cpp
#define SET_ALLIGN_FN(what)                            \
        void set_##what##_fn() { }
        SET_ALLIGN_FN(Left);
#undef SET_ALLIGN_FN
    template<class _Arg> struct Smanip{
            Smanip(void( *pFun)(_Arg), _Arg val):m_pFun(pFun), m_val(val) { }
        void( *m_pFun)(_Arg);
        _Arg m_val;
    };
    template<>  struct Smanip<void> {
        Smanip(void( *pFun)()) : m_pFun(pFun) { }
        void( *m_pFun)();
    };
#define SET_ALLIGN(what)                                      \
    static Smanip<void>  ##what##Allign()                     \
    { return (Smanip<void>(set_##what##_fn)); }
    SET_ALLIGN(Left);
#undef SET_ALLIGN

int main() {  }
D:\temp>cl test.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 17.00.61030 for x86
Copyright (C) Microsoft Corporation.  All rights reserved.

test.cpp
Microsoft (R) Incremental Linker Version 11.00.61030.0
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:test.exe
test.obj

D:\temp>g++ test.cpp
test.cpp:15:23: error: pasting ">" and "Left" does not give a valid preprocessin
g token
     static Smanip<void>  ##what##Allign()  { return (Smanip<void>(set_##what##_
fn)); }
                       ^
test.cpp:16:5: note: in expansion of macro 'SET_ALLIGN'
     SET_ALLIGN(Left);
     ^

我无法理解的是为什么g ++抱怨无效令牌。编译器突出显示>，但这不是宏生成的代码。

Answer 1

在第

行

static Smanip<void>  ##what##Allign()

您尝试连接>和what。尝试使用

static Smanip<void>  what##Allign()

g ++抱怨“在宏上没有给出有效的预处理令牌”，而vc ++编译得很好

1 个答案: