std :: copy vs memcpy的效率 [英] Efficiency of std::copy vs memcpy

问题描述

使用 memcpy 和 std :: copy 之间的效率损失有多严重？

How severe is the efficiency loss between using memcpy and std::copy?

我有一种情况，我的系统上的向量实现似乎没有使用连续的内存，这使得我必须std ::复制其内容后，而不是 memcpy（dest，& vec [0]，size）; 。

I have a situation where the vector implementation on my system doesn't appear to use contiguous memory, which is making me have to std::copy its contents later on rather than doing memcpy(dest, &vec[0], size);. I'm not sure how badly this is likely to impact efficiency.

推荐答案

合理可行的实现会有

A reasonably decent implementation will have std::copy compile to a call memmove in the situations where this is possible (i.e. the element type is a POD).

如果你的实现没有连续的存储（C ++ 03标准需要它）， memmove 可能比 std :: copy ，但可能不会太多。我会开始担心只有当你有测量表明它确实是一个问题。

If your implementation doesn't have contiguous storage (the C++03 standard requires it), memmove might be faster than std::copy, but probably not too much. I would start worrying only when you have measurements to show it is indeed an issue.

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