Question

我正在尝试使用C ++反射方法，并且在理解预处理器宏时遇到了问题。例如，以下代码有效。

header.h：

#define META_PROPERTY(NAME, TYPE, ACCESS, MIN, MAX) \
class NAME##_MetaProperty : public sge::GetSet<TYPE> \
{ \
public: \
    NAME##_MetaProperty(TYPE *NAME) \
        : GetSet(NAME, ACCESS) \
        , min_(MIN) \
        , max_(MAX) \
    {} \

    . . . other methods . . .

private: \
    TYPE min_; \
    TYPE max_; \
}NAME##_prop(&NAME); \

的main.cpp

main
{
    uint32 u(255);
    META_PROPERTY(u, uint32, ACCESS_DEFAULT, 0, 1024);
    ...
}

尽管构造函数不完整，宏仍然很乐意创建NAME ## _ MetaProperty对象，我想我明白了为什么因为预处理器只是填入MIN一个MAX参数。但是，如果我将构造函数更改为以下内容，则会出现一堆编译错误。

public: \
    NAME##_MetaProperty(TYPE *NAME, TYPE MIN, TYPE MAX) \
        : GetSet(NAME, ACCESS) \
        , min_(MIN) \   
        , max_(MAX) \
    {} \

1>d:\projects\sgesuite\tests\test04-reflection\src\main04.cpp(44): error C2143: syntax error: missing ')' before 'constant'
1>d:\projects\sgesuite\tests\test04-reflection\src\main04.cpp(44): error C2143: syntax error: missing ';' before 'constant'
1>d:\projects\sgesuite\tests\test04-reflection\src\main04.cpp(44): error C2059: syntax error: 'constant'
1>d:\projects\sgesuite\tests\test04-reflection\src\main04.cpp(44): error C2059: syntax error: ')'
1>d:\projects\sgesuite\tests\test04-reflection\src\main04.cpp(44): error C2334: unexpected token(s) preceding ':'; skipping apparent function body
1>d:\projects\sgesuite\tests\test04-reflection\src\main04.cpp(44): error C2059: syntax error: '&'
1>d:\projects\sgesuite\tests\test04-reflection\src\main04.cpp(44): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>d:\projects\sgesuite\tests\test04-reflection\src\main04.cpp(44): warning C4183: 'u_prop': missing return type; assumed to be a member function returning 'int'
1>d:\projects\sgesuite\tests\test04-reflection\src\main04.cpp(45): error C2059: syntax error: '='
1>d:\projects\sgesuite\tests\test04-reflection\src\main04.cpp(45): error C2238: unexpected token(s) preceding ';'

如果我预定义常量，我会得到另一组较小的错误。

main
{
    const uint32 min(0);
    const uint32 max(1024);
    META_PROPERTY(u, uint32, ACCESS_DEFAULT, min, max);
}

1>d:\projects\sgesuite\tests\test04-reflection\src\main04.cpp(44): error C2664: 'main::u_MetaProperty::u_MetaProperty(const main::u_MetaProperty &)': cannot convert argument 1 from 'uint32 *' to 'const main::u_MetaProperty &'
1>d:\projects\sgesuite\tests\test04-reflection\src\main04.cpp(44): note: Reason: cannot convert from 'uint32 *' to 'const main::u_MetaProperty'
1>d:\projects\sgesuite\tests\test04-reflection\src\main04.cpp(44): note: No constructor could take the source type, or constructor overload resolution was ambiguous

我只是想了解为什么我不能通过构造函数传递MIN和MAX。这个宏用我的常量做什么？

了解具有常量的预处理器宏

0 个答案: