c#你怎么判断一个字符串是否是数字？

今天在写代码时突然想起测试经常用Microsoft.VisualBasic.Information.IsNumeric判断 url参数是否为数字时的这个方法的效率
因为数字是字符串是直接使用的，所以不需要转型，也就没有用tryparse
结果一测试吓一跳，这个方法的效率是如此的低，再测试了下tryparse还不错，正则的也比较差，
没什么技术含量，看结果吧：

先拓展下字符串：

   public static class Common
    {
        //isDigit
        public static bool isNumberic1(this string _string)
        {
            if (string.IsNullOrEmpty(_string))
                return false;
            foreach (char c in _string)
            {
                if (!char.IsDigit(c))//if(c<'0' || c>'9')//最好的方法,在下面测试数据中再加一个0，然后这种方法效率会搞10毫秒左右
                    return false;
            }
            return true;
        }

        //vb isnumberic
        public static bool isNumberic2(this string _string)
        {
            return !string.IsNullOrEmpty(_string) && Microsoft.VisualBasic.Information.IsNumeric(_string);
        }
        //try parse
        public static bool isNumberic3(this string _string)
        {
            if (string.IsNullOrEmpty(_string))
                return false;
            int i = 0;
            return int.TryParse(_string, out i);
        }

        //try catch
        public static bool isNumberic4(this string _string)
        {
            if (string.IsNullOrEmpty(_string))
                return false;
            try { int.Parse(_string); }
            catch { return false; }
            return true;
        }
        //regex
        public static bool isNumberic5(this string _string)
        {
            return !string.IsNullOrEmpty(_string) && Regex.IsMatch(_string, "^\\d+$");
        }
    }

测试的代码：

class Program
    {
        static void Main(string[] args)
        {

            Test("1234");
            Test("1234a");
            Test("a1234");
            Test("");
            Test(null);
            
        }

        static void Test(string str)
        {
            bool res1 = false, res2 = false, res3 = false, res4 = false, res5 = false;
            Stopwatch wat = new Stopwatch();
            wat.Start();//
            for (int i = 1; i < 100000; i++)
            {
                res1 = str.isNumberic1();
            }
            wat.Stop();
            Console.WriteLine("isDigit      {0}:{1},{2}", str, wat.ElapsedMilliseconds, res1);

            wat.Reset();
            wat.Start();
            for (int i = 1; i < 100000; i++)
            {
                res2= str.isNumberic2();
            }
            wat.Stop();
            Console.WriteLine("isNumberic   {0}:{1},{2}", str, wat.ElapsedMilliseconds, res2);

            wat.Reset();
            wat.Start();
            for (int i = 1; i < 100000; i++)
            {
                res3 = str.isNumberic3();
            }
            wat.Stop();
            Console.WriteLine("try parse    {0}:{1},{2}", str, wat.ElapsedMilliseconds, res3);

            wat.Reset();
            wat.Start();
            for (int i = 1; i < 100000; i++)
            {
                res4 = str.isNumberic4();
            }
            wat.Stop();
            Console.WriteLine("try catch    {0}:{1},{2}", str, wat.ElapsedMilliseconds, res4);

            wat.Reset();
            wat.Start();
            for (int i = 1; i < 100000; i++)
            {
                res5 = str.isNumberic5();
            }
            wat.Stop();
            Console.WriteLine("regex        {0}:{1},{2}", str, wat.ElapsedMilliseconds, res5);
            Console.WriteLine();
        }
    }

下面是我本机的测试结果

isDigit      1234:5,True
isNumberic   1234:166,True
try parse    1234:21,True
try catch    1234:22,True
regex        1234:134,True

isDigit      1234a:5,False
isNumberic   1234a:196,False
try parse    1234a:19,False
try catch    1234a:5182,False
regex        1234a:150,False

isDigit      a1234:2,False
isNumberic   a1234:184,False
try parse    a1234:16,False
try catch    a1234:5084,False
regex        a1234:106,False

isDigit      :1,False
isNumberic   :0,False
try parse    :0,False
try catch    :1,False
regex        :0,False

isDigit      :1,False
isNumberic   :0,False
try parse    :1,False
try catch    :1,False
regex        :0,False

结果：循环判断是否是数字字符效率是最高的
而VisualBasic的方法效率比较低了
顺便测试了下VisualBasic里的left和right方法效率也一样的低，还不及substring的十分之一
所以VisualBasic里虽然有几个方法从名字看来比较好用，实际却比较杯具。

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