Extension method to check whether a string is valid integer, double, bool etc

Question

I'm trying to create an extension method for string that says whether the string is a valid integer, double, bool or decimal. I'm not interested in switch..case and trying to use generics.

Extension method

public static bool Is<T>(this string s)
{
   ....
}

Usage

string s = "23";

if(s.Is<int>())
{
   Console.WriteLine("valid integer");
}

I couldn't able to succeed on implementing the extension method. I'm looking for some ideas/suggestions...

[Why is there no String.IsNumeric Function in C#](http://stackoverflow.com/q/1508668/284240) — Tim Schmelter, Aug 31 '12 at 09:54
Take a look at http://stackoverflow.com/questions/2961656/generic-tryparse — Artur Udod, Aug 31 '12 at 10:00

score 3 · Accepted Answer · edited May 23 '17 at 11:56

This might work using the Cast<>() method:

    public static bool Is<T>(this string s)
    {
        bool success = true;
        try
        {
            s.Cast<T>();
        }
        catch(Exception)
        {
            success = false;
        }
        return success;
    }

EDIT

Obviously this doesn't work every time, so I found another working version here:

public static bool Is<T>(this string input)
{
    try
    {
        TypeDescriptor.GetConverter(typeof(T)).ConvertFromString(input);
    }
    catch
    {
        return false;
    }

    return true;
}

Taken from here.

score 3 · Answer 2 · answered Aug 31 '12 at 09:59

3

Use tryparse :

string someString = "42";
int result;
if(int.TryParse(someString, out result))
{
    // It's ok
     Console.WriteLine("ok: " + result);
}
else
{
    // it's not ok
    Console.WriteLine("Shame on you");
}

answered Aug 31 '12 at 09:59

Steve B

36,818
21
101
174

saj · Answer 3 · 2012-08-31T10:09:37.580

2

This is what you want;

public static bool Is<T>(this string s)
{

    TypeConverter converter = TypeDescriptor.GetConverter(typeof(T));

    try
    {   
        object val = converter.ConvertFromInvariantString(s);
        return true;
    }
    catch
    {
        return false;
    }
}

edited Aug 31 '12 at 10:09

answered Aug 31 '12 at 10:03

saj

4,626
2
26
25

score 1 · Answer 4 · answered Aug 31 '12 at 10:02

Implementation example:

public static class StringExtensions
{
    public static bool Is<T>(this string s)
    {
        if (typeof(T) == typeof(int))
        {
            int tmp;
            return int.TryParse(s, out tmp);
        }

        if (typeof(T) == typeof(long))
        {
            long tmp;
            return long.TryParse(s, out tmp);
        }

        ...

        return false;
    }
}

Usage:

var test1 = "test".Is<int>();
var test2 = "1".Is<int>();
var test3 = "12.45".Is<int>();
var test4 = "45645564".Is<long>();

Also do note that you should take some other parameters as input for the method, such as IFormatProvider to let the user specify the culture to use.

Thanks for answering. But I'm not interested in multiple if statements and I think they make the code hard to maintain. — VJAI, Aug 31 '12 at 10:04
And they actually defeat the whole purpose of using generics — Kevin Gosse, Aug 31 '12 at 10:05

score -2 · Answer 5 · answered Aug 31 '12 at 09:57

-2

I would use a try/catch

string a = "23";

try{

int b = a;

Console.WriteLine("valid integer");

}
catch
{
Console.WriteLine("invalid integer");
}

answered Aug 31 '12 at 09:57

Oedum

796
2
9
28

Extension method to check whether a string is valid integer, double, bool etc

5 Answers5