如何在 C# 中查找指数格式的字符串值？

Question

我想确定字符串是否具有指数格式。目前我正在检查如下。

var s = "1.23E+04";
var hasExponential = s.Contains("E");

但我知道这不是正确的方法。那么谁能指导正确和最快的方法来实现我的要求？

Answer 1

尝试使用正则表达式？

string s = "1.23E+04";
string pattern = @"^\d{1}.\d+(E\+)\d+$";
Regex rgx = new Regex(pattern, RegexOptions.IgnoreCase);
bool hasExponential = rgx.IsMatch(s);

Answer 2

如果您还想确保它确实是一个数字，而不仅仅是其中包含 'E' 的字符串，也许这样的函数会有所帮助。逻辑仍然很简单。

private bool IsExponentialFormat(string str)
{
    double dummy;
    return (str.Contains("E") || str.Contains("e")) && double.TryParse(str, out dummy);
}

Answer 3

你总是可以在 e 上拆分。或者使用 double.TryParse。两者都很好用。（我敢打赌 ParseExponential2 对于有效的更快，而 ParseExponential1 可以对于无效的更快。）

public static void _Main(string[] args)
{
    string[] exponentials = new string[] { "1.23E+4", "1.23E+04", "1.23e+4", "1.23", "1.23e+4e+4", "abce+def", "1.23E-04" };

    for (int i = 0; i < exponentials.Length; i++)
        Console.WriteLine("Input: {0}; Result 1: {1}; Result 2: {2}; Result 3: {3}", exponentials[i], (ParseExponential1(exponentials[i]) ?? 0), (ParseExponential2(exponentials[i]) ?? 0), (ParseExponential3(exponentials[i]) ?? 0));
}

public static double? ParseExponential1(string input)
{
    if (input.Contains("e") || input.Contains("E"))
    {
        string[] inputSplit = input.Split(new char[] { 'e', 'E' });

        if (inputSplit.Length == 2) // If there were not two elements split out, it's an invalid exponential.
        {
            double left = 0;
            int right = 0;

            if (double.TryParse(inputSplit[0], out left) && int.TryParse(inputSplit[1], out right) // Parse the values
                && (left >= -5.0d && left <= 5.0d && right >= -324) // Check that the values are within the range of a double, this is the minimum.
                && (left >= -1.7d && left <= 1.7d && right <= 308)) // Check that the values are within the range of a double, this is the maximum.
            {
                double result = 0;

                if (double.TryParse(input, out result))
                    return result;
            }
        }
    }

    return null;
}

public static double? ParseExponential2(string input)
{
    if (input.Contains("e") || input.Contains("E"))
    {
        double result = 0;

        if (double.TryParse(input, out result))
            return result;
    }

    return null;
}

public static double? ParseExponential3(string input)
{
    double result = 0;

    if (double.TryParse(input, out result))
        return result;

    return null;
}

如果ParseExponential1、ParseExponential2或ParseExponential3returns null则无效。这也允许您同时解析它并获得指示的值。

ParseExponential3 的唯一问题是如果数字不是指数，它也会 return 有效数字。（即，对于 1.23 情况，它将 return 1.23。）

您还可以删除 double 运行ge 的检查。它们只是为了完整性。

此外，为了证明一点，我只是运行下面代码的基准测试，而 nevermoi 的另一个答案中的 Regex 选项将 500ms 变为运行对 exponentials 数组执行 100,000 次，ParseExponential1 选项占用 547ms，ParseExponential2 选项占用 317ms。 sstan 的方法用了 346ms。最后，最快的是我在 134ms 的 ParseExponential3 方法。

string[] exponentials = new string[] { "1.23E+4", "1.23E+04", "1.23e+4", "1.23", "1.23e+4e+4", "abce+def", "1.23E-04" };

Stopwatch sw = new Stopwatch();
sw.Start();
for (int round = 0; round < 100000; round++)
    for (int i = 0; i < exponentials.Length; i++)
        ParseExponential1(exponentials[i]);
sw.Stop();
Console.WriteLine("Benchmark 1 (ParseExponential1) complete: {0}ms", sw.ElapsedMilliseconds);

sw.Reset();

sw.Start();
for (int round = 0; round < 100000; round++)
    for (int i = 0; i < exponentials.Length; i++)
        ParseExponential2(exponentials[i]);
sw.Stop();
Console.WriteLine("Benchmark 2 (ParseExponential2) complete: {0}ms", sw.ElapsedMilliseconds);
sw.Reset();
string pattern = @"^\d{1}.\d+(E\+)\d+$";
Regex rgx = new Regex(pattern, RegexOptions.IgnoreCase);

sw.Start();
for (int round = 0; round < 100000; round++)
    for (int i = 0; i < exponentials.Length; i++)
        rgx.IsMatch(exponentials[i]);
sw.Stop();
Console.WriteLine("Benchmark 3 (Regex Parse) complete: {0}ms", sw.ElapsedMilliseconds);
sw.Reset();

sw.Start();
for (int round = 0; round < 100000; round++)
    for (int i = 0; i < exponentials.Length; i++)
        IsExponentialFormat(exponentials[i]);
sw.Stop();
Console.WriteLine("Benchmark 4 (IsExponentialFormat) complete: {0}ms", sw.ElapsedMilliseconds);

sw.Start();
for (int round = 0; round < 100000; round++)
    for (int i = 0; i < exponentials.Length; i++)
        ParseExponential3(exponentials[i]);
sw.Stop();
Console.WriteLine("Benchmark 5 (ParseExponential3) complete: {0}ms", sw.ElapsedMilliseconds);

并添加了以下方法：

private static bool IsExponentialFormat(string str)
{
    double dummy;
    return (str.Contains("E") || str.Contains("e")) && double.TryParse(str, out dummy);
}

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