成员初始化列表的顺序 [英] Order of member initialization list

问题描述

在多次简化我的代码之后，我发现导致问题的原因如下.

After simplifying my code for many times, I found the following cause the problem.

class B {
public:
    B(const int x)
              :_x(x) {}
    const int _x;
};

class C {
public:
    C(const B& b) 
        : _b(b), _b2(_b._x) {}
    B _b2;       // line 1
    const B& _b; // line 2
};

int main() {
    B b(1);
    C c(b);
}

警告(clang 8.0.0)

Warning (clang 8.0.0)

test16.cpp:11:22: warning: reference '_b' is not yet bound to a value when used here [-Wuninitialized]
        : _b(b), _b2(_b._x) {}
                     ^
1 warning generated.

g ++-6编译程序.运行该程序会导致分段错误.

g++-6 compiles the program. Running the program causes segmentation fault.

类成员的初始化是否遵循成员初始化列表(: _b(b), _b2(_b._x))的顺序或类中成员的顺序(如B _b2; const B& _b;)?

Does the initialization of members of a class follows the order of the member initialization list (: _b(b), _b2(_b._x)) or the order of the members in the class (like B _b2; const B& _b;) ?

推荐答案

成员变量的初始化按照在类中声明它们的顺序进行.

Initialization of member variables occurs in the order that they are declared in the class.

http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rc-order

和:

http://en.cppreference.com/w/cpp/language/initializer_list

3)然后，按以下顺序初始化非静态数据成员 类定义中的声明.

3) Then, non-static data members are initialized in order of declaration in the class definition.

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