复制构造函数不是继承的 [英] Copy constructor is not inherited

问题描述

我有以下代码：

class C {
public:
    C(int) {}
    C(const C&) {}
    C() {}
};  

class D : public C { 
public:
    using C::C;
};  

int main() {
    C c;
    D d_from_c(c); // does not compile, copy ctor is not inherited
    D d_from_int(1); // compiles, C(int) is inherited
}   

派生类应该继承所有ctors除了默认的ctor之外（解释为这里）。但为什么拷贝ctor不是继承的呢？相关问题的参数在这里是不可接受的。

Derived class should inherit all ctors of base except the default ctor (it is explained here). But why copy ctor is not inherited as well? Arguments from the related question are not acceptable here.

代码使用g ++ 4.8.1编译。

The code is compiled with g++ 4.8.1.

推荐答案

因为标准这么说。 [class.inhctor] / p3，强调我的：

Because the standard says so. [class.inhctor]/p3, emphasis mine:

对于候选的继承的
构造函数中的每个非模板构造函数除了没有参数的构造函数或具有单个参数的
复制/移动构造函数，构造函数是
隐式声明具有相同的构造函数特性，除非
一个用户声明的构造函数，在
complete类中使用using-declaration出现时具有相同的签名，或者构造函数
是该类的默认，复制或移动构造函数。

For each non-template constructor in the candidate set of inherited constructors other than a constructor having no parameters or a copy/move constructor having a single parameter, a constructor is implicitly declared with the same constructor characteristics unless there is a user-declared constructor with the same signature in the complete class where the using-declaration appears or the constructor would be a default, copy, or move constructor for that class.

这篇关于复制构造函数不是继承的的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！