Determine if a string is numeric

Demonstrates how to implement a custom IsNumeric method in other .NET/Mono languages that do not wish to reference the Microsoft.VisualBasic.dll assembly.

VB.NET

Compiler: Microsoft (R) Visual Basic Compiler version 8.0

Dim Value As String = "123"
If IsNumeric(Value) Then
    
End If

C#

Compiler: Microsoft (R) Visual C# 2005 Compiler version 8.00

public static bool IsNumeric(string s) { double Result; return double.TryParse(s, out Result); }

       string Value = "123";
       If (IsNumeric(Value)) {
       }

Perl

Quoting from perlfaq4:

How do I determine whether a scalar is a number/whole/integer/float?

Assuming that you don't care about IEEE notations like "NaN" or "Infinity", you probably just want to use a regular expression.

         if (/\D/)            { print "has nondigits\n" }
         if (/^\d+$/)         { print "is a whole number\n" }
         if (/^-?\d+$/)       { print "is an integer\n" }
         if (/^[+-]?\d+$/)    { print "is a +/- integer\n" }
         if (/^-?\d+\.?\d*$/) { print "is a real number\n" }
         if (/^-?(?:\d+(?:\.\d*)?&\.\d+)$/) { print "is a decimal number\n" }
         if (/^([+-]?)(?=\d&\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?$/)
                              { print "a C float\n" }

There are also some commonly used modules for the task. Scalar::Util (distributed with 5.8) provides access to perl's internal function "looks_like_number" for determining whether a variable looks like a number. Data::Types exports functions that validate data types using both the above and other regular expressions. Thirdly, there is "Regexp::Common" which has regular expressions to match various types of numbers. Those three modules are available from the CPAN.

If you're on a POSIX system, Perl supports the "POSIX::strtod" function. Its semantics are somewhat cumbersome, so here's a "getnum" wrapper function for more convenient access. This function takes a string and returns the number it found, or "undef" for input that isn't a C float. The "is_numeric" function is a front end to "getnum" if you just want to say, Is this a float?

          sub getnum {
              use POSIX qw(strtod);
              my $str = shift;
              $str =~ s/^\s+//;
              $str =~ s/\s+$//;
              $! = 0;
              my($num, $unparsed) = strtod($str);
              if (($str eq ) && ($unparsed != 0) && $!) {
                  return undef;
              } else {
                  return $num;
              }
          }

          sub is_numeric { defined getnum($_[0]) }

Or you could check out the String::Scanf module on the CPAN instead. The POSIX module (part of the standard Perl distribution) provides the "strtod" and "strtol" for converting strings to double and longs, respectively.

PHP

<?php
$string = '123';
if(is_numeric($string)) {
}

Python

s = '123'
try:
  i = int(s)
  # use i
except ValueError:
  # s is not numeric

Or:

   s = '123'
   if s.isdigit():
       ...

Java

String s = "123";
try {
  int i = Integer.parseInt(s);
  // use i
}
catch (Exception e) {
  // s is not numeric
}

ColdFusion

Adobe's ColdFusion

<cfset TestValue=34>
  TestValue: <cfoutput>#TestValue#</cfoutput>

<cfif isNumeric(TestValue)>
  is Numeric.
<cfelse>
  is NOT Numeric.
</cfif>

<cfset TestValue="NAS">
  TestValue: <cfoutput>#TestValue#</cfoutput>

<cfif isNumeric(TestValue)>
  is Numeric.
<cfelse>
  is NOT Numeric.
</cfif>