在构造函数C ++中初始化成员向量 [英] Initialize member vector in constructor C++

问题描述

我有一个类，该类的成员类型为 vector< CCPoint> .我想在构造函数调用中初始化此成员，如何实现呢?

I have a class that has a member with type vector<CCPoint>. I want to initialize this member in the constructor call, how can achieve it?

我是这样的:

.h

class A{
    public:
        A(vector<CCPoint> *p);
    private:
        vector<CCPoint> *p;
}

.cpp

A:A(){
    this->p = p;
}

致电

Vector<CCPoint> *p = new Vector<CCPoint>;
A a = new A(p);

推荐答案

这将泄漏内存，因为没有人会删除您新建"的矢量.

This will leak memory, because nobody is deleting the vector you "new"-ed.

此外，为什么根本没有指向矢量的指针?您是否担心将其复制到构造函数中会很昂贵?

Also, why have a pointer to a vector at all? Are you worried about copying it into the constructor being expensive?

将成员更改为向量:

class A{
    public:
        A(vector<CCPoint> p);
    private:
        vector<CCPoint> p;
}

更改构造函数以使用初始化程序列表:

Change the constructor to use the initialiser list:

A:A(vector<CCPoint> newP) : p(newP){
    // Empty
}

然后这样呼叫:

Vector<CCPoint> p;
A a(p);

永远不要使用"new"创建对象，除非您确切地知道为什么这样做，即使这样，也要重新考虑.

Never, ever create an object with "new" unless you know exactly why you are doing so, and even then, reconsider.

性能注意:是的，此可能会导致矢量复制的发生，具体取决于编译器对复制的选择.另一种C ++ 11花哨的裤子解决方案是使用move:

Performance Note: Yes this may cause a vector copy to occur, depending on copy elision by the compiler. An alternative C++11 fancy pants solution would be to use move:

class A{
    public:
        A(vector<CCPoint> p);
    private:
        vector<CCPoint> p;
}

A:A(vector<CCPoint> newP) : p(std::move(newP)){
    // Empty
}

Vector<CCPoint> p;
A a(std::move(p)); // After this completes, 'p' will no longer be valid.

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