C ++最佳实践：返回引用与对象 [英] C++ best practice: Returning reference vs. object

问题描述

我正在尝试学习C ++，并试图了解返回的对象。我似乎看到了两种方法，并且需要了解什么是最佳实践。

I'm trying to learn C++, and trying to understand returning objects. I seem to see 2 ways of doing this, and need to understand what is the best practice.

选项1：

QList<Weight *> ret;
Weight *weight = new Weight(cname, "Weight");
ret.append(weight);
ret.append(c);
return &ret;

选项2：

QList<Weight *> *ret = new QList();
Weight *weight = new Weight(cname, "Weight");
ret->append(weight);
ret->append(c);
return ret;

（当然，我也许也不了解）。

(of course, I may not understand this yet either).

哪种方法被认为是最佳实践，应该遵循？

Which way is considered best-practice, and should be followed?

推荐答案

选项1 是有缺陷的。声明对象时

Option 1 is defective. When you declare an object

QList<Weight *> ret;

它仅存在于本地范围内。函数退出时销毁它。但是，您可以使用

it only lives in the local scope. It is destroyed when the function exits. However, you can make this work with

return ret; // no "&"

现在，尽管 ret 被销毁了，

Now, although ret is destroyed, a copy is made first and passed back to the caller.

这是通常首选的方法。实际上，复制和销毁操作（实际上什么也没做）通常被消除或优化后，您将获得一个快速，优雅的程序。

This is the generally preferred methodology. In fact, the copy-and-destroy operation (which accomplishes nothing, really) is usually elided, or optimized out and you get a fast, elegant program.

选项2 有效，但是您有了指向堆的指针。查看C ++的一种方法是该语言的目的是避免诸如此类的手动内存管理。有时您确实想管理堆上的对象，但是选项1仍然允许：

Option 2 works, but then you have a pointer to the heap. One way of looking at C++ is that the purpose of the language is to avoid manual memory management such as that. Sometimes you do want to manage objects on the heap, but option 1 still allows that:

QList<Weight *> *myList = new QList<Weight *>( getWeights() );

其中 getWeights 是您的示例函数。 （在这种情况下，您可能必须定义一个副本构造函数 QList :: QList（QList const&），但是像前面的示例一样，它可能不会被调用。 ）

where getWeights is your example function. (In this case, you may have to define a copy constructor QList::QList( QList const & ), but like the previous example, it will probably not get called.)

同样，您可能应该避免使用指针列表。该列表应直接存储对象。尝试使用 std :: list …练习语言功能比练习实现数据结构更重要。

Likewise, you probably should avoid having a list of pointers. The list should store the objects directly. Try using std::list… practice with the language features is more important than practice implementing data structures.

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