Realloc等价于C ++ [英] Realloc equivalent in C++

问题描述

是的，另一个 realloc 与 std :: vector 问题。我知道你要说什么，我同意，忘记手动内存分配，只需使用 std :: vector 。很遗憾，我的教授禁止我使用STL中的任何东西来完成这个任务。

所以，我有一个动态数组 T ，我需要它可以调整大小，我不能使用 std :: vector 。我可以回到黑暗的年龄，做整个事情与 malloc 和家庭，但如果我可以使用新

我读过很多线程，每个人都说不，你不能做，使用 std ::向量，但他们都在2011年8月之前发布，我希望反对希望，自从C ++ 11的黎明以来可能有一些改变。

解决方案

你应该避免使用 realloc 完全无论如何，因为你不能移动这样的C ++对象。

• 使用 buf = new unsigned char [sizeof（T）* capacity] 创建新缓冲区


• 将分配的 unsigned char * 转换为 T * 并从现在起使用这些 T -pointers


• 通过placement new ，如 new（& buf [i]）T（original_copy）


• 更大的缓冲区，首先分配新的缓冲区，使用 std :: uninitialized_copy （ not std :: copy ），然后使用 buf [i]。〜T（）销毁旧的元素中的元素并使用 delete [ ] buf 。

所有这些都假设您不必担心异常安全，

请注意，在现实世界的代码中，你必须保证异常安全，这是一个比这更加乏味。 p>

Yes, another realloc vs. std::vector question. I know what you're going to say, and I agree, forget manual memory allocation, and just use a std::vector. Well unfortunately my professor has forbidden me to use anything from the STL for this assignment.

So yeah, I have a dynamic array of T and I need it to be resizable, and I can't use std::vector. I could return to the dark ages and do the whole thing with malloc and family, but if I could use new that would be totally awesome.

I've read plenty of threads where everyone said "no, you can't do it, use std::vector", but they were all posted before August 2011, and I'm hoping against hope that something might have changed since the dawn of C++11. So tell me, am I in luck, or do I have to revert to C style memory allocation?

解决方案

You should avoid realloc completely anyway, because you can't move around C++ objects like that.

• Use buf = new unsigned char[sizeof(T) * capacity] to create a new buffer
• Cast the allocated unsigned char * to T * and use these T-pointers from now on
• Construct new elements via "placement new", as in new (&buf[i]) T(original_copy)
• To copy the buffer to a larger buffer, allocate the new one first, use std::uninitialized_copy (not std::copy), then destroy the elements in the old one using buf[i].~T() and deallocate the old buffer using delete [] buf.

All of this is assuming you don't have to worry about exception-safety, which is probably OK for the assignment.
Just be aware that in real-world code you'd have to guarantee exception safety and it's a lot more tedious than this.

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