具有相同名称的纯虚函数的不同实现 [英] Distinct implementations for pure virtual functions with same name

问题描述

可能重复：

继承共享方法名称的接口

我有两个基类 I1 和 I2 与纯虚函数 void R 0; 。我想让派生类 IImpl 继承 I1 和 I2 并且有 I1 :: R（）和 I2 :: R（）的不同实现。

I have two base classes I1 and I2 with pure virtual functions void R() = 0;. I want the derived class IImpl to inherit from I1 and I2 and to have distinct implementations for I1::R() and I2::R().

以下代码在MS VS 2005和2010中编译和工作。我在语言扩展禁用和警告级别4下编译。没有警告和错误。

The code below compiles and works in MS VS 2005 and 2010. I compile with Language Extension disabled and on warning level 4. There are no warnings and no errors.

我在gcc 4.2中尝试过相同的代码。它不编译。 GCC报告错误：

I tried the same code in gcc 4.2. It does not compile. GCC reports an error:

error: cannot define member function 'I1::R' within 'IImpl'

我的问题是：

1. 为什么这段代码在MS VS中工作，为什么它不能在gcc中工作？


2. 代码是标准C ++吗？


3. 实现它的正确方法是什么，因此它是一个标准C ++并在VS和gcc上编译？

谢谢！

#include <stdio.h>

class I1
{
public:
    virtual void R() = 0;
    virtual ~I1(){}
};

class I2
{
public:
    virtual void R() = 0;
    virtual ~I2(){}
};

class IImpl: public I1, public I2
{
public:

    virtual void I1::R()
    {
        printf("I1::R()\r\n");
    }

    virtual void I2::R()
    {
        printf("I2::R()\r\n");
    }
};

int main(int argc, char* argv[])
{
    IImpl impl;

    I1 *p1 = &impl;
    I2 *p2 = &impl;

    p1->R();
    p2->R();

    return 0;
}

推荐答案

，根据8.3 / 1

This code is non-standard, according to 8.3/1

声明符-id除了成员函数（9.3）成员（9.4）在类外，...

A declarator-id shall not be qualified except for the definition of a member function (9.3) or static data member (9.4) outside of its class,...

，所以你不能限定成员函数名声明/班上。这就是为什么它不是由gcc编译。

so you can't qualify member function names when declaring/defining them inside the class. That's why it isn't compiled by gcc.

MSVC似乎有一个非标准扩展允许这样的代码。我想这是为C ++管理扩展，这是明确的接口实现是如此做，虽然它很久以前已被弃用，似乎仍然支持语法。

MSVC seems to have a non-standard extension allowing such code. I guess it was done for Managed Extensions for C++, that's exactly how explicit interface implementations were done there and although it was deprecated long ago seems that syntax is still supported.

A正确的方式，它在链接由BjörnPollex提供。

A correct way to implent it is decribed at the link provided by Björn Pollex.

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