C++ 在空指针上使用 new
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Using new on void pointer
提问by Brandon
int main()
{
void* Foo = new???
delete Foo;
}
How do you do something like the above? You can't put new void[size]. And I don't want to know how to do it with malloc()and free(). I already know that works. I'm curious and want to know how it's done with new and delete.
你如何做类似上面的事情？你不能放new void[size]。我不想知道如何用malloc()and来做free()。我已经知道那行得通。我很好奇，想知道 new 和 delete 是如何完成的。
I googled this and saw something about operator new(size); and operator delete(size);
我用谷歌搜索了这个，看到了一些关于operator new(size); 和operator delete(size);
What is the difference between those and new/ delete? Why does C++ not just allow new void* [size]?
这些和new/ 有delete什么区别？为什么 C++ 不仅仅允许 new void* [size]？
回答by ybungalobill
This will do the trick:
这将解决问题：
int main()
{
void* Foo = ::operator new(N);
::operator delete(Foo);
}
These operators allocate/deallocate raw memory measured in bytes, just like malloc.
这些运算符分配/释放以字节为单位的原始内存，就像malloc.
回答by Oliver Charlesworth
Why does C++ not just allow new void[size]?
为什么 C++ 不仅仅允许 new void[size]？
Because voidis not an object; it has no size! How much space should be allocated? Bear in mind that new T[size]is approximatelyequivalent to malloc(sizeof(T) * size).
因为void不是对象；它没有大小！应该分配多少空间？记住，new T[size]是大致等同于malloc(sizeof(T) * size)。
If you just want a raw byte array, then you could use char.*
如果您只想要一个原始字节数组，那么您可以使用char. *
* Although, of course, because this is C++ you should use something like
std::vector<char>to avoid memory-leak and exception-safety issues.* 当然，因为这是 C++，所以你应该使用类似的东西std::vector<char>来避免内存泄漏和异常安全问题。回答by Dietmar Kühl
C++ travels in constructed objects allocated using some variation of new T. or new T[n]for some type T. If you really need uninitialized memory (it is very rare that you do), you can allocate/deallocate it using operator new()and operator delete():
C++ 在使用new T. 或new T[n]对于某些类型T。如果你真的需要未初始化的内存（你很少这样做），你可以使用operator new()and分配/取消分配它operator delete()：
void* ptr = operator new(size);
operator delete(ptr);
(similarily for the array forms)
（类似于数组形式）
回答by 0x499602D2
void *is convertible to any pointer type. You can simply do void *Foo = new intor any other type that you want. But there really isn't a reason to do this in C++.
void *可转换为任何指针类型。你可以简单地做void *Foo = new int或任何其他你想要的类型。但是真的没有理由在 C++ 中这样做。
回答by my_username
You could do
你可以做
void* data = new char[num_of_bytes];
to allocate some memory, in a similar fashion as malloc
以类似于 malloc 的方式分配一些内存
