c# - 解析性能(If、TryParse、Try-Catch)

Question

我非常了解处理解析文本以获取信息的不同方法。例如，对于解析整数，可以预期什么样的性能。我想知道是否有人知道这方面的任何好的统计数据。我正在寻找测试过这个的人的一些真实数字。

其中哪些在哪些情况下提供最佳性能？

Parse(...)  // Crash if the case is extremely rare .0001%

If (SomethingIsValid) // Check the value before parsing
    Parse(...)

TryParse(...) // Using TryParse

try
{
    Parse(...)
}
catch
{
    // Catch any thrown exceptions
}

Answer 1

总是使用T.TryParse(string str, out T value)。抛出异常代价高昂，如果您可以先验 处理这种情况，则应该避免这种情况。使用 try-catch block 来“节省”性能(因为您的无效数据率很低)是对异常处理的滥用，以牺牲可维护性和良好的编码实践为代价。遵循合理的软件工程开发实践，编写测试用例，运行应用程序，然后进行基准测试和优化。

"We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil. Yet we should not pass up our opportunities in that critical 3%" -Donald Knuth

因此，您可以像在碳信用额度中那样任意指定 try-catch 的性能较差，而 TryParse 的性能较好。只有在我们运行我们的应用程序并确定我们有某种减速 w.r.t. 之后。我们甚至会考虑使用 TryParse 以外的任何字符串解析。

(编辑:因为提问者似乎想要计时数据来提供好的建议，这里是请求的计时数据)

来自用户的 10,000 个输入的各种失败率的时间(对于非信徒):

Failure Rate      Try-Catch          TryParse        Slowdown
  0%           00:00:00.0131758   00:00:00.0120421      0.1
 10%           00:00:00.1540251   00:00:00.0087699     16.6
 20%           00:00:00.2833266   00:00:00.0105229     25.9
 30%           00:00:00.4462866   00:00:00.0091487     47.8
 40%           00:00:00.6951060   00:00:00.0108980     62.8
 50%           00:00:00.7567745   00:00:00.0087065     85.9
 60%           00:00:00.7090449   00:00:00.0083365     84.1
 70%           00:00:00.8179365   00:00:00.0088809     91.1
 80%           00:00:00.9468898   00:00:00.0088562    105.9
 90%           00:00:01.0411393   00:00:00.0081040    127.5
100%           00:00:01.1488157   00:00:00.0078877    144.6


/// <param name="errorRate">Rate of errors in user input</param>
/// <returns>Total time taken</returns>
public static TimeSpan TimeTryCatch(double errorRate, int seed, int count)
{
    Stopwatch stopwatch = new Stopwatch();
    Random random = new Random(seed);
    string bad_prefix = @"X";

    stopwatch.Start();
    for(int ii = 0; ii < count; ++ii)
    {
        string input = random.Next().ToString();
        if (random.NextDouble() < errorRate)
        {
           input = bad_prefix + input;
        }

        int value = 0;
        try
        {
            value = Int32.Parse(input);
        }
        catch(FormatException)
        {
            value = -1; // we would do something here with a logger perhaps
        }
    }
    stopwatch.Stop();

    return stopwatch.Elapsed;
}

/// <param name="errorRate">Rate of errors in user input</param>
/// <returns>Total time taken</returns>
public static TimeSpan TimeTryParse(double errorRate, int seed, int count)
{
    Stopwatch stopwatch = new Stopwatch();
    Random random = new Random(seed);
    string bad_prefix = @"X";

    stopwatch.Start();
    for(int ii = 0; ii < count; ++ii)
    {
        string input = random.Next().ToString();
        if (random.NextDouble() < errorRate)
        {
           input = bad_prefix + input;
        }

        int value = 0;
        if (!Int32.TryParse(input, out value))
        {
            value = -1; // we would do something here with a logger perhaps
        }
    }
    stopwatch.Stop();

    return stopwatch.Elapsed;
}

public static void TimeStringParse()
{
    double errorRate = 0.1; // 10% of the time our users mess up
    int count = 10000; // 10000 entries by a user

    TimeSpan trycatch = TimeTryCatch(errorRate, 1, count);
    TimeSpan tryparse = TimeTryParse(errorRate, 1, count);

    Console.WriteLine("trycatch: {0}", trycatch);
    Console.WriteLine("tryparse: {0}", tryparse);
}