返回一个指向std :: vector内的对象 [英] returning a pointed to an object within a std::vector

问题描述

我有一个非常基本的问题，返回一个向量的元素的引用。

I have a very basic question on returning a reference to an element of a vector .

有一个向量 vec ，用于存储类 Foo 。我想从这个向量访问一个元素。 （不想使用向量索引）。我应该如何编写方法 getFoo 这里？

There is a vector vec that stores instances of class Foo. I want to access an element from this vector . ( don't want to use the vector index) . How should I code the method getFoo here?

#include<vector>
#include<stdio.h>
#include<iostream>
#include<math.h>

using namespace std;
class Foo {      
      public:
             Foo(){};
             ~Foo(){};
};


class B {
      public:
             vector<Foo> vec;
             Foo* getFoo();
             B(){};
             ~B(){};
};


Foo* B::getFoo(){
int i;
vec.push_back(Foo());
i = vec.size() - 1;

// how to return a pointer to vec[i] ??

return vec.at(i);

};

int main(){
    B b;
    b = B();
    int i  = 0;
    for (i = 0; i < 5; i ++){
        b.getFoo();   
        }

    return 0;
}

推荐答案

为什么使用指针你可以返回一个引用？

Why use pointers at all when you can return a reference?

Foo& B::getFoo() {
    vec.push_back(Foo());
    return vec.back();
}

请注意，引用，指针和迭代器到

Note that references, pointers and iterators to a vectors contents get invalidated if reallocation occurs.

还有成员资料公开（例如您的 vec here）不是好的做法 - 最好根据需要为您的类提供访问方法。

Also having member data public (like your vec here) isn't good practice - it is better to provide access methods for your class as needed.

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