字串是否为某个类型的数值

有时候需要判断一个字串是不是一个int/double/float.
C#没有直接的方法实现，可以自己用如下几个方法实现：
<1>try-catch

 class Program
    {
        public static bool IsInt32(string s)
        {
            try 
            {
                int n = Int32.Parse(s);
                return true;
            }
            catch
            {
                return false;
            }
        }       
        static void Main(string[] args)
        {
            string str = "123456789101112";            
            Console.WriteLine("{0}!", str = (IsInt32(str) ? "Yes":"No"));            
        }
    }

<2>正则表达式

using System.Text.RegularExpressions;
class Program
    {

        static void Main(string[] args)
        {
            string str = "12345678910111a2222";  
            Regex rex = new Regex(@"^\d+\d$");
            Console.WriteLine("{0}!", str = (rex.IsMatch(str) ? "Yes" : "No"));            
        }
    }

效率比较

class Program
    {
        static int times = 10000000;

        public static bool TryCatch(string s)
        {
            try
            {
                int n = Int32.Parse(s);
                return true;
            }
            catch
            {
                return false;
            }
        }
        public static bool IsNumber(string s)
        {
            foreach (char c in s)
            {
                if (c < '0' || c > '9')
                    return false;
            }
            return true;
        }


        static void Main(string[] args)
        {

            string str = "1234567891";
            int rx, tc, isn;
            Regex rex = new Regex(@"^\d+\d$");
            int counter;

            counter = System.Environment.TickCount;
            for (int i = 0; i < times; i++)
            {
                IsNumber(str);
            }
            counter = System.Environment.TickCount - counter;
            isn = counter;
            Console.WriteLine("InNumber time:{0}ms!", isn);

            counter = System.Environment.TickCount;
            for (int i = 0; i < times; i++)
            {
                rex.IsMatch(str);
            }
            counter = System.Environment.TickCount - counter;
            rx = counter;
            Console.WriteLine("Regex time:{0}ms!", rx);

            counter = System.Environment.TickCount;
            for (int i = 0; i < times; i++)
            {
                TryCatch(str);
            }
            counter = System.Environment.TickCount - counter;
            tc = counter;
            Console.WriteLine("TryCatch time:{0}ms!", tc);      

            Console.WriteLine("InNumber:Regex:TryCatch = {0} : {1} : {2}",tc/isn, tc/rx, tc/tc);
            //Console.WriteLine("InNumber:TryCatch:Regex = {0} : {1} : {2}",rx/isn, rx/tc, rx/rx);
        }

可以发现，trycatch 在有没有抛出异常的情况下，差别很大。
要是有异常，那么IsNumber ：Regex : trycatch = 446 : 68 : 1
要没有异常，那么IsNumber : trycatch ：Regex = 7 : 4 : 1
但无论如何，自己写的函数始终是最快的。