我们可以重载malloc（）吗？ [英] Can we overload malloc()?

问题描述

和删除之后，我在一本书中阅读了 new 和 malloc em>是新的调用构造函数，返回调用变量的类型，第三个区别是我们可以重载 new 在类的基础上，而 malloc

解决方案

:: operator new 在全局命名空间中可以替换（覆盖），不重载。这将导致使用覆盖而不是标准库提供的函数。并且可以提供 my_class :: operator new ，因此它将用于 new my_class 表达式，重载

重新载入新只有在您使用刊登位置 new 语法：

  new（memory_pool，123，other_args）my_class（constructor_args）
  

在 new 关键字后，在括号中提供额外的参数， c $ c> operator new 被调用，在 size_t 之后附加额外的参数，指定需要多少内存。

你可以重载 :: malloc 就像任何其他函数，通过定义一个版本，它采用不同的参数：

  void * malloc（std :: size_t size，allocation_pool& pool）; 
  

这只是一个刚刚被调用的新函数 malloc 。但是最好通过显式的 std :: 限定来调用库函数，并添加一个 std :: malloc

您不能替换 std :: malloc 。唯一可以替换的函数是 :: operator new 的标准变量。没有类特定的 malloc ，因为它没有参数指示什么类将进入返回的内存块。 malloc 不知道你将使用返回的内存做什么;

作为程序组织的一个问题，一个更专用的分配器应该被赋予和调用作为另一个名字，而不是 malloc 。如果您需要根据类型调用不同的函数，请使用模板，例如

  template< typename allocated> 
 void * my_allocate（std :: size_t sz）; //也许szparam是不必要的。 
  

您还可以专门化 std :: allocator< my_class> 及其成员函数 allocate 。然后各种标准库设施将调用您的函数，尽管没有自定义 new 。 （你可以避免太深入到自定义新，因为它的怪癖。）

i went through overloading new and delete, I was reading in a book that the difference between new and malloc is that new call the constructor,returns the type of calling variable and the third difference is that we can overload new on class by class basis, whereas malloc cant be, can someone explain this class by class basis also.

解决方案

::operator new in the global namespace can be replaced (overridden), not overloaded. This causes the override to be used instead of the function provided by the standard library. And my_class::operator new can be provided so it will be used in new my_class expressions, which is also different from overloading.

Overloading new only comes into play when you use the placement new syntax:

new ( memory_pool, 123, other_args ) my_class( constructor_args )

Providing extra arguments in parens after the new keyword causes another overload of operator new to be called, with the extra arguments appended after the size_t specifying how much memory is needed.

You can certainly overload ::malloc just like any other function, by defining a version which takes different arguments:

void *malloc( std::size_t size, allocation_pool &pool );

This is just a new function that happens to be called malloc. But it's better to call library functions with an explicit std:: qualification, and adding a std::malloc overload would be against the library's rules.

You can't replace std::malloc. The only functions that can be replaced are the standard variants of ::operator new. There is no such thing as a class-specific malloc because it doesn't take an argument indicating the what class will go into the returned memory block. malloc has no idea what you will be doing with the returned memory; it's just a blob of bytes.

As a matter of program organization, a more specialized allocator should probably be given and called as another name, not malloc. If you have a need to call different functions depending on the type, use a template, e.g.

template< typename allocated >
void *my_allocate( std::size_t sz ); // maybe "sz" param is unnecessary.

You might also specialize std::allocator< my_class > and its member function allocate. Then various standard library facilities will call your function despite no customization of new. (You might avoid getting too deep into custom new because of its quirks.)

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