其中使用 - “操作员新”或“operator new []” - 在C ++中分配一个原始内存块？ [英] Which to use - "operator new" or "operator new[]" - to allocate a block of raw memory in C++?

问题描述

我的C ++程序需要一个未初始化的内存块和一个 void * 指向该块的指针，以便我可以将它提供给第三方库。我想将块生存期的控制传递给库，所以我不想使用 std :: vector 。当库完成块，它将调用我必须提供的回调，并将释放该块。在CI中将使用 malloc（）和更高版本 free（）。

My C++ program needs a block of uninitialized memory and a void* pointer to that block so that I can give it to a third party library. I want to pass control of the block lifetime to the library, so I don't want to use std::vector. When the library is done with the block it will call a callback that I have to supply and that will deallocate the block. In C I would use malloc() and later free().

在C ++中，我可以调用 :: operator new 或 :: operator new [] 和 :: operator delete 或操作符delete [] 分别以后：

In C++ I can either call ::operator new or ::operator new[] and ::operator delete or operator delete[] respectively later:

void* newBlock = ::operator new( sizeOfBlock );
// then, later
::operator delete( newBlock );

看起来像 :: operator new :: operator new [] 具有完全相同的签名和完全相同的行为。对于 :: operator delete 和 :: operator delete [] 也是如此。我不应该做的唯一的配对 operator new 与 operator delete [] ，反之亦然 - 未定义的行为。除此之外，我选择哪对，为什么？

Looks like both ::operator new and ::operator new[] have exactly the same signature and exactly the same behavior. The same for ::operator delete and ::operator delete[]. The only thing I shouldn't do is pairing operator new with operator delete[] and vice versa - undefined behavior. Other than that which pair do I choose and why?

推荐答案

使用单个对象和使用 new > new [] 与对象数组。因此，例如：

Use new with a single object and new[] with an array of objects. So, for example:

int* x = new int; // Allocates single int
int* y = new int[5]; // Allocates an array of integers

*x = 10; // Assignment to single value
y[0] = 8; // Assignment to element of the array

如果你正在做的就是分配一个内存缓冲区，然后分配一个 char 如：

int bufferlen = /* choose a buffer size somehow */
char* buffer = new char[bufferlen];
// now can refer to buffer[0] ... buffer[bufferlen-1]

你应该真正使用 std :: vector 任意数组，你应该使用 std :: string

However, in C++, you should really use std::vector for arbitrary arrays, and you should use std::string for character arrays that are to be interpreted or used as strings.

没有理由调用 :: operator new 或 :: operator new [] ，而不是使用这些调用的普通语法。对于POD和原始类型（例如 char ），不会进行初始化。如果你需要一个 void * 缓冲区，那么只需使用 static_cast 来转换 char * 到 void * 。

There is no reason to invoke ::operator new or ::operator new[] explicitly rather than using the ordinary syntax for these calls. For POD and primitive types (e.g. char) no initialization will take place. If you need to get a void* buffer, then simply use static_cast to convert char* to void*.

这篇关于其中使用 - “操作员新”或“operator new []” - 在C ++中分配一个原始内存块？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！