为什么函数isprefix比C#中的Startswith更快? [英] Why is function isprefix faster than Startswith in C#?

问题描述

有人知道为什么C#(.NET)的 StartsWith 函数比 IsPrefix ?

Does anyone know why C# (.NET)'s StartsWith function is considerably slower than IsPrefix?

推荐答案

我认为这主要是在获取线程的当前文化.

I think it's mostly fetching the thread's current culture.

如果您将Marc的测试更改为使用String.StartsWith的这种形式:

If you change Marc's test to use this form of String.StartsWith:

    Stopwatch watch = Stopwatch.StartNew();
    CultureInfo cc = CultureInfo.CurrentCulture;
    for (int i = 0; i < LOOP; i++)
    {
        if (s1.StartsWith(s2, false, cc)) chk++;
    }
    watch.Stop();
    Console.WriteLine(watch.ElapsedMilliseconds + "ms; chk: " + chk);

距离更近了.

如果使用s1.StartsWith(s2, StringComparison.Ordinal)，它比使用CompareInfo.IsPrefix快得多(当然取决于CompareInfo).在我的盒子上，结果是(不是科学地):

If you use s1.StartsWith(s2, StringComparison.Ordinal) it's a lot faster than using CompareInfo.IsPrefix (depending on the CompareInfo of course). On my box the results are (not scientifically):

• s1.StartsWith(s2):6914ms
• s1.StartsWith(s2，false，culture):5568ms
• compare.IsPrefix(s1，s2):5200ms
• s1.StartsWith(s2，StringComparison.Ordinal):1393毫秒

显然是因为它实际上只是比较每个点的16位整数，这非常便宜.如果您不想想要进行文化敏感的检查，那么和的性能对您尤为重要，那就是我要使用的重载.

Obviously that's because it's really just comparing 16 bit integers at each point, which is pretty cheap. If you don't want culture-sensitive checking, and performance is particularly important to you, that's the overload I'd use.

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