全局非抛出 ::operator new 和 std::malloc 的区别

2021-12-24 00:00:00 memory-management malloc c++ new-operator c++11

C++ 有几个函数来获取动态存储，其中大多数在一些基本方式上有所不同.操作系统通常会添加更多.

C++ has several functions to acquire dynamic storage, most of which differ in some fundamental way. Several more are usually added by the OS.

由于它们的可移植性和相似性，其中两个特别有趣:malloc 和 ::operator new.

Two of these are of special interest due to their portability and similarity: malloc and ::operator new.

全局 void* operator new(size_t, ::std::nothrow&) 和 void* malloc(size_t)<之间有什么区别吗?/代码>?

Are there any differences (w.r.t. the standard and implementation) between the global void* operator new(size_t, ::std::nothrow&) and void* malloc(size_t)?

由于我所说的似乎有些混乱，请考虑以下两个调用:

Since there seems to be some confusion what I am talking about, consider the following two calls:

void* p = ::std::malloc(10);
void* q = ::operator new(10, ::std::nothrow);

明显而微不足道的区别是如何释放内存:

The obvious and trivial difference is how to deallocate the memory:

::std::free(p);
::operator delete(q);

注意:这个问题不是例如的重复new/delete 和 malloc/free 有什么区别? 因为它谈到使用 global operator new 实际上并不执行任何 ctor 调用.

Note: This question is not a duplicate of e.g. What is the difference between new/delete and malloc/free? since it talks about using the global operator new that does not actually perform any ctor calls.

推荐答案

除了语法和 free 与 delete 之外，主要区别是

The main differences, aside from syntax and free vs. delete, are

  1. 你可以便携地替换 ::operator新的;
  2. malloc 带有 realloc，对于 new 没有等效项；
  3. new 具有 的概念new_handler，没有对应的 malloc.
  1. you can portably replace ::operator new;
  2. malloc comes with realloc, for which new has no equivalent;
  3. new has the concept of a new_handler, for which there is no malloc equivalent.

(替换 malloc 会打开一个 蠕虫病毒.它可以完成，但不可移植，因为它需要链接器的知识.)

(Replacing malloc opens up a can of worms. It can be done, but not portably, because it requires knowledge of the linker.)

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