“free”是安全的吗？由`new'分配的内存？ [英] Is it safe to `free()` memory allocated by `new`?

问题描述

我正在处理一个C ++库，其中的一个函数返回一个（新分配）指针到一个双精度数组。 API声明调用者负责释放内存。

I'm working on a C++ library, one of whose functions returns a (freshly allocated) pointer to an array of doubles. The API states that it is the responsibility of the caller to deallocate the memory.

但是，C ++库曾经在C中实现，并且该函数分配内存与 malloc（）。它还假设调用者将用 free（）释放该内存。

However, that C++ library used to be implemented in C and the function in question allocates the memory with malloc(). It also assumes that the caller will deallocate that memory with free().

我可以安全地替换调用 malloc（）调用 new ？将现有的客户端代码（使用 free（）断开如果我这样做？迄今为止我可以找到的是 free ，其中指出

Can I safely replace the call to malloc() with a call to new? Will the existing client code (that uses free() break if I do so? All I could find so far was the official documentation of free(), which states that

如果ptr没有指向分配有[malloc，calloc

If ptr does not point to a block of memory allocated with [malloc, calloc or realloc], it causes undefined behavior.

但我相信这是在C ++自带的分配操作符之前编写的。

But I believe this was written before C++ came along with its own allocation operators.

推荐答案

您不能混合搭配 malloc 和免费与新和删除草案C ++标准回到C99标准如果我们转到 C ++标准草案 20.6.13 C库（强调我的未来）：

You are not allowed to mix and match malloc and free with new and delete the draft C++ standard refers back to the C99 standard for this and if we go to the draft C++ standard section 20.6.13 C library it says (emphasis mine going forward):

内容与标准C库标头stdlib.h相同，但有以下更改：

The contents are the same as the Standard C library header stdlib.h, with the following changes:

和：

函数calloc（），malloc（）和realloc尝试通过调用:: operator
new（）（18.6）分配存储。

The functions calloc(), malloc(), and realloc() do not attempt to allocate storage by calling ::operator new() (18.6).

和：

函数free（）不会通过调用:: operator delete（）来释放存储空间。
另请参见：ISO C条款7.11.2。

The function free() does not attempt to deallocate storage by calling ::operator delete(). See also: ISO C Clause 7.11.2.

并包括其他更改，分配给 new 的内容免费。因此，C99标准草案中的 7.20.3.2 部分的自由功能仍然是正确的参考，它说：

and includes other changes, none of which state that we can use free on contents allocated with new. So section 7.20.3.2 The free function from the draft C99 standard is still the proper reference and it says:

否则，如果参数与calloc，malloc或realloc函数先前返回的指针不匹配，或者如果空间已被释放或重新分配，行为未定义。

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