C ++堆栈变量和堆变量 [英] C++ stack variables and heap variables

问题描述

当你在C ++中创建一个新的对象时，我们可以这样做：

When you create a new object in C++ that lives on the stack, (the way I've mostly seen it) you do this:

CDPlayer player;

在堆上创建一个对象时，调用 new ：

When you create an object on the heap you call new:

CDPlayer* player = new CDPlayer();

但是当你这样做：

CDPlayer player=CDPlayer();

它创建一个基于堆栈的对象，但它和顶部示例之间的区别是什么？

it creates a stack based object, but whats the difference between that and the top example?

推荐答案

PODs的区别很重要（基本上，所有内置类型如 int ， bool ， double 等加上类似于C的结构体和仅从其他POD构建的联合体）是默认初始化和值初始化之间的差异。对于POD，一个简单的

The difference is important with PODs (basically, all built-in types like int, bool, double etc. plus C-like structs and unions built only from other PODs), for which there is a difference between default initialization and value initialization. For PODs, a simple

T obj;

将保留 obj 未初始化， c $ c> T（）默认初始化对象。所以

will leave obj uninitialized, while T() default-initializes the object. So

T obj = T();

是确保对象正确初始化的好方法。

is a good way to ensure that an object is properly initialized.

这在模板代码中特别有用，其中 T 可能是POD或非POD类型。当您知道 T 不是POD类型时， T obj; 就足够了。

This is especially helpful in template code, where T might either a POD or a non-POD type. When you know that T is not a POD type, T obj; suffices.

附录： 您也可以写

Addendum: You can also write

T* ptr = new T; // note the missing ()

> T 是POD）。

(and avoid initialization of the allocated object if T is a POD).

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