C ++指针数组初始化帮助 [英] C++ pointer array initialization help

问题描述

我在初始化指针数组时遇到麻烦。我发现用gcc c ++（4.6.0）编译是：

  MyClass ** a = new MyClass * ; 
  

不总是初始化指针数组。 （大部分时间它给我一个空指针数组，这让我困惑）

  MyClass ** a = new MyClass * （100）。 
  

DOES将数组中的所有指针初始化为0（空指针）。

我写的代码意味着可以在Windows / Linux / Mac / BSD平台上移植。这是gcc c ++编译器的一个特殊功能吗？还是标准的C ++？

解决方案

这个值初始化是标准C ++。

相关的标准是C ++ 98和C ++ 03§5.3.4/ 15。在C ++ 98它是默认初始化，在C + + 03和以后它的值初始化。对你的指针，他们都减少到零初始化。

C ++ 03§5.3.4/ 15：

< blockquote>

–如果 new-initializer 是（）形式，则该项目是值初始化的（8.5）;

在C ++ 0x中，该段落改为引用初始化规则8.5用于直接初始化，其中N3290 FDIS），你发现在§8.5/ 16中有相同的措辞。

hth。，

I had trouble with initializing arrays of pointers. What I found out compiling with gcc c++ (4.6.0) is:

MyClass** a = new MyClass*[100];

Does not always initalize the array of pointers. (most of the time it did give me an array of null pointers which confused me)

MyClass** a = new MyClass*[100]();

DOES initialize all the pointers in the array to 0 (null pointer).

The code I'm writing is meant to be be portable across Windows/Linux/Mac/BSD platforms. Is this a special feature of the gcc c++ compiler? or is it standard C++? Where in the standard does it says so?

解决方案

This value-initialization is standard C++.

The relevant standardeese is in C++98 and C++03 §5.3.4/15. In C++98 it was default-initialization, in C++03 and later it's value initialization. For your pointers they both reduce to zero-initialization.

C++03 §5.3.4/15:

– If the new-initializer is of the form (), the item is value-initialized (8.5);

In C++0x that paragraph instead refers to “the initialization rules of 8.5 for direct-initialization”, where in N3290 (the FDIS) you find about the same wording in §8.5/16.

Cheers & hth.,

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