在构造函数中冒号是什么意思？ [英] What does the colon mean in a constructor?

问题描述

可能的重复项：

C ++奇怪的构造函数语法

构造函数中的冒号后的变量

在C ++构造函数名后面有冒号（：）是什么？

对于下面的C ++函数：

For the C++ function below:

cross(vector<int> &L_, vector<bool> &backref_, vector< vector<int> > &res_) : 

    L(L_), c(L.size(), 0), res(res_), backref(backref_) {

    run(0); 

}

冒号（：）告诉关系之间的左右部分？可能，这段代码可以说什么？

What does the colon (":") tell the relationships between its left and right part? And possibly, what can be said from this piece of code?

推荐答案

这是一种在c类之前初始化类成员字段的方法

This is a way to initialize class member fields before the c'tor of the class is actually called.

假设你有：

class A {

  private:
        B b;
  public:
        A() {
          //Using b here means that B has to have default c'tor
          //and default c'tor of B being called
       }
}

现在通过写入：

class A {

  private:
        B b;
  public:
        A( B _b): b(_b) {
          // Now copy c'tor of B is called, hence you initialize you
          // private field by copy of parameter _b
       }
}

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