C ++枚举标志与位集 [英] C++ enum flags vs bitset

问题描述

枚举标志上使用位集的利弊是什么？

What are pros/cons of usage bitsets over enum flags?

namespace Flag {
    enum State {
        Read   = 1 << 0,
        Write  = 1 << 1,
        Binary = 1 << 2,
    };
}

namespace Plain {
    enum State {
        Read,
        Write,
        Binary,
        Count
    };
}

int main()
{
    {
        unsigned int state = Flag::Read | Flag::Binary;
        std::cout << state << std::endl;

        state |= Flag::Write;
        state &= ~(Flag::Read | Flag::Binary);
        std::cout << state << std::endl;
    } {
        std::bitset<Plain::Count> state;
        state.set(Plain::Read);
        state.set(Plain::Binary);
        std::cout << state.to_ulong() << std::endl;

        state.flip();
        std::cout << state.to_ulong() << std::endl;
    }

    return 0;
}

正如我到目前为止所看到的，比特集具有更方便的置位/清除/翻转函数来处理，但是使用枚举标志是一种更广泛使用的方法。

As I can see so far, bitsets have more convinient set/clear/flip functions to deal with, but enum-flags usage is a more wide-spreaded approach.

比特集的缺点可能是什么？在日常代码中应使用什么时间？ ？

What are possible downsides of bitsets and what and when should I use in my daily code?

推荐答案

您编译时启用了优化功能吗？

Do you compile with optimization on? It is very unlikely that there is a 24x speed factor.

对我来说，位集比较好，因为它可以为您管理空间：

To me, bitset is superior, because it manages space for you:

• 可以根据需要扩展。如果您有很多标志，则 int / long long 版本的空间可能会用完。


• 可能会占用更少的空间，如果您仅使用几个标志（它可以放入 unsigned char / unsigned简短的-我不确定实现是否会应用此优化）

• can be extended as much as wanted. If you have a lot of flags, you may run out of space in the int/long long version.
• may take less space, if you only use just several flags (it can fit in an unsigned char/unsigned short - I'm not sure that implementations apply this optimization, though)

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