Question

说我有3节课;主类，头等舱和第二类。

在第一类和第二类中我定义了一个MACRO（名称 - CLASS_NAME），宏的目的是在每个类中我将宏重新定义为className或其他任何东西以在其函数中使用该宏。

代码的结构如下

Class First，Second和Main都有宏CLASS_NAME 类名（例如“first”，“second”，“main”）作为值。
Class Second包括First并覆盖此宏值和另外声明了另一个宏PRINT_CLASS_NAME 打印CLASS_NAME宏。
Class First没有这个PRINT_CLASS_NAME宏，所以我有声明了一个函数指针，并使用a从Main类设置它的值拉姆达。
Class Main包括First和Second，并重新定义宏CLASS_NAME。要检查输出，请参阅Main.cpp文件

Class First - 头文件

#pragma once
#include <iostream>
#include <functional>

#undef CLASS_NAME 
#define CLASS_NAME "first"

class First
{
public:
    First();
    ~First();

    // simple class that prints the value of CLASS_NAME
    void printClassName();
    // sets the function pointer
    void setPrintClassName(std::function<void()> inFunctionPointer);
    // The function pointer that holds the lambda to show CLASS_NAME's value
    std::function<void()> mPrintClassFromSecond;
};

Class First - 源文件

#include "First.h"

First::First()
{
    std::cout << "Class First : Constructor" << "\n";
}
First::~First()
{
}

void First::printClassName()
{
    std::cout << "Class name from function : " << CLASS_NAME << "\n";
}

void First::setPrintClassName(std::function<void()> inFunctionPointer)
{
    mPrintClassFromSecond = inFunctionPointer;
}

第二类 - 头文件

#pragma once
#include "First.h"
#include <functional>

#undef CLASS_NAME
#define CLASS_NAME "second"

#define PRINT_CLASS_NAME std::cout << "Class name from Macros: " << CLASS_NAME << "\n"

class Second
{
public:
    Second();
    ~Second();
};

第二类 - 源文件

#include "Second.h"

Second::Second()
{
    std::cout << "Class Second : Constructor" << "\n";
    PRINT_CLASS_NAME;
}
Second::~Second()
{
}

Main.cpp的

// MacrosWithFunctionPointerProblem.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
// after including First.h the CLASS_NAME macro value for this class is "first"
#include "First.h"
// after including Second.h the CLASS_NAME macro value for this class is "second"
#include "Second.h"

// after this the CLASS_NAME macro value for this class is "main"
#undef CLASS_NAME
#define CLASS_NAME "main"

int main()
{
    First _first;
    // outputs CLASS_NAME value "first" which is expected
    _first.printClassName();
    // sets lambda to use macro PRINT_CLASS_NAME
    _first.setPrintClassName([](){ PRINT_CLASS_NAME; });
    // outputs CLASS_NAME value "main" which was not expected by me
    _first.mPrintClassFromSecond();

    // outputs CLASS_NAME value "first" which is expected
    Second _second;

    std::getchar();
    return 0;
}

输出：

Class First : Constructor
Class name from function : first
Class name from Macros: main
Class Second : Constructor
Class name from Macros: second

问题：乳清我得到的是宏“CLASS_NAME而不是”第一“的”主“。如何避免将“main”作为CLASS_NAME的值并将“first”作为值？

PS：我尽量尽量减少问题，所以如果我留下任何可能有助于您更好地理解问题的重要细节，请在评论中提出。

Answer 1

MACRO是没有范围的文本替换，所以在

中

_first.setPrintClassName([](){ PRINT_CLASS_NAME; });

PRINT_CLASS_NAME变为std::cout << "Class name from Macros: " << CLASS_NAME << "\n"

此处的

和CLASS_NAME已被（重新）定义为"main"。

使用lambda时出现意外的宏值

1 个答案: