String::New：这是什么？

发布于 2024-09-06 07:26:04 字数 252 浏览 4 评论 0原文

我有Java背景，正在学习C++。我遇到了以下 C++ 代码：

String source = String::New("'Hello' + ', World'");

据我所知，这应该是对“String”类的静态成员函数“New”的调用。但是，我搜索了定义“String”的整个头文件，在 String 类或其超类中没有任何名为“New”的静态成员。 C++ 中的 String 类或 New 成员函数有什么特殊含义吗？

原文

I am from a Java background and is learning C++. I encountered the following C++ code:

String source = String::New("'Hello' + ', World'");

As what I understand so far, this should be a call to static member function 'New' of class 'String'. But, I've searched through the whole header file defining 'String', there is not any static member named 'New' in the String class or its super classes. Is there any special meaning attached to String class or the New member function in C++?

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寄风 2024-09-13 07:26:04

你是对的。即调用 String 类上的 static 方法 New。

C++（或 STL）没有原生的 String 类，有一个 string 类，但它没有 >::新方法。您必须确保您正在阅读正确的文档:)

它可能是从基类继承的，因此请确保检查 String 是否是继承层次结构的一部分。

这是 v8 的 String 的处理。这很有趣。

有两种实现：

v8::String - 外部可见的（这里是 doxygen 文档显示类层次结构）。
v8::internal::String - 内部表示。

浏览内部字符串源代码，String是实际上是一个代表 JavaScript 字符串的堆分配对象。

事实证明，Google Code 的 UI 已损坏（也许它们有最大字符数？）。 v8::internal::HeapObject 源代码应该位于 src/objects.h 中，但该文件已被截断。外部可见的 v8::String 源代码应该位于 include/v8.h 中，但它也被截断。

您可以下载源代码并查看文件。它是这样说的：

/**
 * A JavaScript string value (ECMA-262, 4.3.17).
 */
class V8EXPORT String : public Primitive {
 public:
   ...

 /**
   * Allocates a new string from either utf-8 encoded or ascii data.
   * The second parameter 'length' gives the buffer length.
   * If the data is utf-8 encoded, the caller must
   * be careful to supply the length parameter.
   * If it is not given, the function calls
   * 'strlen' to determine the buffer length, it might be
   * wrong if 'data' contains a null character.
   */
  static Local<String> New(const char* data, int length = -1);

  /** Allocates a new string from utf16 data.*/
  static Local<String> New(const uint16_t* data, int length = -1);

  ...
};

You are correct. That is calling the static method New on the String class.

C++ (or STL) doesn't have a native String class, there is a string class, but it doesn't have a ::New method. You'll have to make sure you're reading the right documentation :)

It's possible that it's inherited from a base-class, so make sure you check if String is part of an inheritance hierarchy.

Here's the deal with v8's String. It's interesting.

There are two implementations:

v8::String - the externally visible one (Here is doxygen documentation showing the class hierarchy).
v8::internal::String - the internal representation.

Browsing the internal String source code, String is indeed a heap allocated object representing a Javascript string.

It turns out that Google Code's UI is broken (maybe they have a maximum character count?). The v8::internal::HeapObject source code should be in src/objects.h, but the file is truncated. And the externally visible v8::String source code should be in include/v8.h, but it too is truncated.

You can download the source and view the files. Here is what it says:

/**
 * A JavaScript string value (ECMA-262, 4.3.17).
 */
class V8EXPORT String : public Primitive {
 public:
   ...

 /**
   * Allocates a new string from either utf-8 encoded or ascii data.
   * The second parameter 'length' gives the buffer length.
   * If the data is utf-8 encoded, the caller must
   * be careful to supply the length parameter.
   * If it is not given, the function calls
   * 'strlen' to determine the buffer length, it might be
   * wrong if 'data' contains a null character.
   */
  static Local<String> New(const char* data, int length = -1);

  /** Allocates a new string from utf16 data.*/
  static Local<String> New(const uint16_t* data, int length = -1);

  ...
};

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