Copy constructors

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[编辑] 语法

[编辑] 解释

• 初始化，T a = b;或T a(b);，其中b是类型T

  Original:

  initialization, T a = b; or T a(b);, where b is of type T

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• 函数参数传递：f(a);，a的类型是T和f是void f(T t)

  Original:

  function argument passing: f(a);, where a is of type T and f is void f(T t)

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• 函数返回：return a;T f()，a类型T，如没有采取任何构造函数一个函数内部.

  Original:

  function return: return a; inside a function such as T f(), where a is of type T, which has no move constructor.

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[编辑] 隐式声明的拷贝构造函数

• 所有直接和虚拟基础T的拷贝构造函数的引用为const或作为其第一个参数为const波动

  Original:

  all direct and virtual bases of T have copy constructors with references to const or to const volatile as their first parameters

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• 所有非静态成员T的拷贝构造函数的引用为const或作为其第一个参数为const波动

  Original:

  all non-static members of T have copy constructors with references to const or to const volatile as their first parameters

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[编辑] 删除隐式声明的拷贝构造函数

• T非静态数据成员不能被复制（已删除，无法访问，或含糊不清的拷贝构造函数）

  Original:

  T has non-static data members that cannot be copied (have deleted, inaccessible, or ambiguous copy constructors)

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• T有直接或虚基类，它不能被复制（已删除，无法访问，或含糊不清的拷贝构造函数）

  Original:

  T has direct or virtual base class that cannot be copied (has deleted, inaccessible, or ambiguous copy constructors)

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• T有直接或虚基类被删除或无法访问的析构函数

  Original:

  T has direct or virtual base class with a deleted or inaccessible destructor

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• T有一个用户定义的移动构造函数或移动赋值运算符（C++11 起）

  Original:

  T has a user-defined move constructor or move assignment operator （C++11 起）

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• T是工会，有一个变体成员与非平凡的拷贝构造函数（C++11 起）

  Original:

  T is a union and has a variant member with non-trivial copy constructor （C++11 起）

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• T右值引用类型的数据成员（C++11 起）

  Original:

  T has a data member of rvalue reference type （C++11 起）

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[编辑] 琐碎的拷贝构造函数

• T没有虚成员函数

  Original:

  T has no virtual member functions

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• T没有虚基类

  Original:

  T has no virtual base classes

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• 选择每一个直接基础T的拷贝构造函数是微不足道的

  Original:

  The copy constructor selected for every direct base of T is trivial

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• 选择每一个非静态类类型（或类类型的数组）星期四会员T的拷贝构造函数是微不足道的

  Original:

  The copy constructor selected for every non-static class type (or array of class type) memeber of T is trivial

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[编辑] 隐式定义拷贝构造函数

[编辑] 注释

[编辑] 为例

struct A {
    int n;
    A(int n=1) : n(n) {}
    A(const A& a) : n(a.n) {} // user-defined copy ctor
};
 
struct B : A {
    // implicit default ctor B::B()
    // implicit copy ctor B::B(const B&) 
};
 
struct C : B {
     C() : B() {}
 private:
     C(const C&); // non-copiable, C++98 style
};
 
int main()
{
    A a1(7);
    A a2(a1); // calls the copy ctor
    B b;
    B b2 = b;
    A a3 = b; // conversion to A& and copy ctor
    volatile A va(10);
    // A a4 = va; // compile error
 
    C c;
    // C c2 = c; // compile error
}