What is the C equivalent of NaN or IsNumeric

Question

What is the most efficient way of testing an input string whether it contains a numeric value  or conversely Not A Number   I guess I can use Double Parse or a regex  see below  but I was wondering if there is some built in way to do this  such as javascript s NaN   or IsNumeric    was that VB  I can t remember     public static bool IsNumeric this string value        return Regex IsMatch value      d

User · Answer

This is a modified version of the solution proposed by Mr Siir. I find that adding an extension method is the best solution for reuse and simplicity in the calling method.

public static bool IsNumeric(this String s)
{
    try { double.Parse(s); return true; }
    catch (Exception) { return false; }
}

I modified the method body to fit on 2 lines and removed the unnecessary .ToString() implementation. For those not familiar with extension methods here is how to implement:

Create a class file called ExtensionMethods. Paste in this code:

using System;
using System.Collections.Generic;
using System.Text;

namespace YourNameSpaceHere
{
    public static class ExtensionMethods
    {
        public static bool IsNumeric(this String s)
        {
            try { double.Parse(s); return true; }
            catch (Exception) { return false; }
        }
    }
}

Replace YourNameSpaceHere with your actual NameSpace. Save changes. Now you can use the extension method anywhere in your app:

bool validInput = stringVariable.IsNumeric();

Note: this method will return true for integers and decimals, but will return false if the string contains a comma. If you want to accept input with commas or symbols like "$" I would suggest implementing a method to remove those characters first then test if IsNumeric.

User · Answer

I was using Chris Lively s snippet  selected answer  encapsulated in a bool function like Gishu s suggestion for a year or two   I used it to make sure certain query strings were only numeric before proceeding with further processing   I started getting some errant querystrings that the marked answer was not handling  specifically  whenever a comma was passed after a number like  3645    returned true    This is the resulting mod      static public bool IsNumeric string s             double myNum   0        if  Double TryParse s  out myNum                    if  s Contains       return false           return true                else                  return false

User · Answer

I prefer something like this  it lets you decide what NumberStyle to test for   public static Boolean IsNumeric String input  NumberStyles numberStyle        Double temp      Boolean result   Double TryParse input  numberStyle  CultureInfo CurrentCulture  out temp       return result

User · Answer

public static bool IsNumeric string anyString        if  anyString    null                anyString                  if  anyString Length  gt  0                double dummyOut   new double            System Globalization CultureInfo cultureInfo   new System Globalization CultureInfo  en-US   true           return Double TryParse anyString  System Globalization NumberStyles Any  cultureInfo NumberFormat  out dummyOut             else               return false

User · Answer

VB has the IsNumeric function  You could reference Microsoft VisualBasic dll and use it

User · Answer

I prefer something like this  it lets you decide what NumberStyle to test for   public static Boolean IsNumeric String input  NumberStyles numberStyle        Double temp      Boolean result   Double TryParse input  numberStyle  CultureInfo CurrentCulture  out temp       return result

User · Answer

public static bool IsNumeric string anyString        if  anyString    null                anyString                  if  anyString Length  gt  0                double dummyOut   new double            System Globalization CultureInfo cultureInfo   new System Globalization CultureInfo  en-US   true           return Double TryParse anyString  System Globalization NumberStyles Any  cultureInfo NumberFormat  out dummyOut             else               return false

User · Answer

This is a modified version of the solution proposed by Mr Siir. I find that adding an extension method is the best solution for reuse and simplicity in the calling method.

public static bool IsNumeric(this String s)
{
    try { double.Parse(s); return true; }
    catch (Exception) { return false; }
}

I modified the method body to fit on 2 lines and removed the unnecessary .ToString() implementation. For those not familiar with extension methods here is how to implement:

Create a class file called ExtensionMethods. Paste in this code:

using System;
using System.Collections.Generic;
using System.Text;

namespace YourNameSpaceHere
{
    public static class ExtensionMethods
    {
        public static bool IsNumeric(this String s)
        {
            try { double.Parse(s); return true; }
            catch (Exception) { return false; }
        }
    }
}

Replace YourNameSpaceHere with your actual NameSpace. Save changes. Now you can use the extension method anywhere in your app:

bool validInput = stringVariable.IsNumeric();

Note: this method will return true for integers and decimals, but will return false if the string contains a comma. If you want to accept input with commas or symbols like "$" I would suggest implementing a method to remove those characters first then test if IsNumeric.

User · Answer

This doesn t have the regex overhead  double myNum   0  String testVar    Not A Number    if  Double TryParse testVar  out myNum          it is a number   else        it is not a number     Incidentally  all of the standard data types  with the glaring exception of GUIDs  support TryParse   update secretwep brought up that the value  2345   will pass the above test as a number   However  if you need to ensure that all of the characters within the string are digits  then another approach should be taken   example 1     public Boolean IsNumber String s      Boolean value   true    foreach Char c in s ToCharArray          value   value  amp  amp  Char IsDigit c          return value      or if you want to be a little more fancy  public Boolean IsNumber String value      return value All Char IsDigit       update 2   from  stackonfire to deal with null or empty strings   public Boolean IsNumber String s         Boolean value   true       if  s    String Empty    s    null             value false         else            foreach Char c in s ToCharArray                   value   value  amp  amp  Char IsDigit c                     return value

User · Answer

Actually  Double NaN is supported in all  NET versions 2 0 and greater

User · Answer

Yeah  IsNumeric is VB   Usually people use the TryParse   method  though it is a bit clunky   As you suggested  you can always write your own     int i  if  int TryParse string  out i

User · Answer

I prefer something like this  it lets you decide what NumberStyle to test for   public static Boolean IsNumeric String input  NumberStyles numberStyle        Double temp      Boolean result   Double TryParse input  numberStyle  CultureInfo CurrentCulture  out temp       return result

User · Answer

In addition to the previous correct answers it is probably worth pointing out that  Not a Number   NaN  in its general usage is not equivalent to a string that cannot be evaluated as a numeric value  NaN is usually understood as a numeric value used to represent the result of an  impossible  calculation - where the result is undefined  In this respect I would say the Javascript usage is slightly misleading  In C  NaN is defined as a property of the single and double numeric types and is used to refer explicitly to the result of diving zero by zero  Other languages use it to represent different  impossible  values

User · Answer

I know this has been answered in many different ways  with extensions and lambda examples  but a combination of both for the simplest solution   public static bool IsNumeric this String s        return s All Char IsDigit       or if you are using Visual Studio 2015  C  6 0 or greater  then  public static bool IsNumeric this String s    gt  s All Char IsDigit     Awesome C 6 on one line   Of course this is limited because it just tests for only numeric characters     To use  just have a string and call the method on it  such as   bool IsaNumber    123456  IsNumeric

User · Answer

In addition to the previous correct answers it is probably worth pointing out that  Not a Number   NaN  in its general usage is not equivalent to a string that cannot be evaluated as a numeric value  NaN is usually understood as a numeric value used to represent the result of an  impossible  calculation - where the result is undefined  In this respect I would say the Javascript usage is slightly misleading  In C  NaN is defined as a property of the single and double numeric types and is used to refer explicitly to the result of diving zero by zero  Other languages use it to represent different  impossible  values

User · Answer

I prefer something like this  it lets you decide what NumberStyle to test for   public static Boolean IsNumeric String input  NumberStyles numberStyle        Double temp      Boolean result   Double TryParse input  numberStyle  CultureInfo CurrentCulture  out temp       return result

User · Answer

This doesn t have the regex overhead  double myNum   0  String testVar    Not A Number    if  Double TryParse testVar  out myNum          it is a number   else        it is not a number     Incidentally  all of the standard data types  with the glaring exception of GUIDs  support TryParse   update secretwep brought up that the value  2345   will pass the above test as a number   However  if you need to ensure that all of the characters within the string are digits  then another approach should be taken   example 1     public Boolean IsNumber String s      Boolean value   true    foreach Char c in s ToCharArray          value   value  amp  amp  Char IsDigit c          return value      or if you want to be a little more fancy  public Boolean IsNumber String value      return value All Char IsDigit       update 2   from  stackonfire to deal with null or empty strings   public Boolean IsNumber String s         Boolean value   true       if  s    String Empty    s    null             value false         else            foreach Char c in s ToCharArray                   value   value  amp  amp  Char IsDigit c                     return value

User · Answer

I have a slightly different version which returns the number   I would guess that in most cases after testing the string you would want to use the number   public bool IsNumeric string numericString  out Double numericValue        if  Double TryParse numericString  out numericValue           return true      else         return false

User · Answer

This doesn t have the regex overhead  double myNum   0  String testVar    Not A Number    if  Double TryParse testVar  out myNum          it is a number   else        it is not a number     Incidentally  all of the standard data types  with the glaring exception of GUIDs  support TryParse   update secretwep brought up that the value  2345   will pass the above test as a number   However  if you need to ensure that all of the characters within the string are digits  then another approach should be taken   example 1     public Boolean IsNumber String s      Boolean value   true    foreach Char c in s ToCharArray          value   value  amp  amp  Char IsDigit c          return value      or if you want to be a little more fancy  public Boolean IsNumber String value      return value All Char IsDigit       update 2   from  stackonfire to deal with null or empty strings   public Boolean IsNumber String s         Boolean value   true       if  s    String Empty    s    null             value false         else            foreach Char c in s ToCharArray                   value   value  amp  amp  Char IsDigit c                     return value

User · Answer

You can still use the Visual Basic function in C    The only thing you have to do is just follow my instructions shown below    Add the reference to the Visual Basic Library by right clicking on your project and selecting  Add Reference        Then import it in your class as shown below   using Microsoft VisualBasic  Next use it wherever you want as shown below               if   Information IsNumeric softwareVersion                         throw new DataException string Format    0   is an invalid App Version   Only numeric values are supported at this time    softwareVersion                 Hope  this helps and good luck

User · Answer

Maybe this is a C  3 feature  but you could use double NaN

User · Answer

You can still use the Visual Basic function in C    The only thing you have to do is just follow my instructions shown below    Add the reference to the Visual Basic Library by right clicking on your project and selecting  Add Reference        Then import it in your class as shown below   using Microsoft VisualBasic  Next use it wherever you want as shown below               if   Information IsNumeric softwareVersion                         throw new DataException string Format    0   is an invalid App Version   Only numeric values are supported at this time    softwareVersion                 Hope  this helps and good luck

User · Answer

VB has the IsNumeric function  You could reference Microsoft VisualBasic dll and use it

User · Answer

I like the extension method  but don t like throwing exceptions if possible  I opted for an extension method taking the best of 2 answers here            lt summary gt          Extension method that works out if a string is numeric or not          lt  summary gt           lt param name  str  gt string that may be a number lt  param gt           lt returns gt true if numeric  false if not lt  returns gt      public static bool IsNumeric this String str                double myNum   0          if  Double TryParse str  out myNum                         return true                    return false

User · Answer

Maybe this is a C  3 feature  but you could use double NaN

User · Answer

In addition to the previous correct answers it is probably worth pointing out that  Not a Number   NaN  in its general usage is not equivalent to a string that cannot be evaluated as a numeric value  NaN is usually understood as a numeric value used to represent the result of an  impossible  calculation - where the result is undefined  In this respect I would say the Javascript usage is slightly misleading  In C  NaN is defined as a property of the single and double numeric types and is used to refer explicitly to the result of diving zero by zero  Other languages use it to represent different  impossible  values

User · Answer

Yeah  IsNumeric is VB   Usually people use the TryParse   method  though it is a bit clunky   As you suggested  you can always write your own     int i  if  int TryParse string  out i

User · Answer

VB has the IsNumeric function  You could reference Microsoft VisualBasic dll and use it

User · Answer

Simple extension   public static bool IsNumeric this String str        try               Double Parse str ToString             return true            catch             return false

User · Answer

I have a slightly different version which returns the number   I would guess that in most cases after testing the string you would want to use the number   public bool IsNumeric string numericString  out Double numericValue        if  Double TryParse numericString  out numericValue           return true      else         return false

User · Answer

I like the extension method  but don t like throwing exceptions if possible  I opted for an extension method taking the best of 2 answers here            lt summary gt          Extension method that works out if a string is numeric or not          lt  summary gt           lt param name  str  gt string that may be a number lt  param gt           lt returns gt true if numeric  false if not lt  returns gt      public static bool IsNumeric this String str                double myNum   0          if  Double TryParse str  out myNum                         return true                    return false

User · Answer

Yeah  IsNumeric is VB   Usually people use the TryParse   method  though it is a bit clunky   As you suggested  you can always write your own     int i  if  int TryParse string  out i

User · Answer

Yeah  IsNumeric is VB   Usually people use the TryParse   method  though it is a bit clunky   As you suggested  you can always write your own     int i  if  int TryParse string  out i

User · Answer

This doesn t have the regex overhead  double myNum   0  String testVar    Not A Number    if  Double TryParse testVar  out myNum          it is a number   else        it is not a number     Incidentally  all of the standard data types  with the glaring exception of GUIDs  support TryParse   update secretwep brought up that the value  2345   will pass the above test as a number   However  if you need to ensure that all of the characters within the string are digits  then another approach should be taken   example 1     public Boolean IsNumber String s      Boolean value   true    foreach Char c in s ToCharArray          value   value  amp  amp  Char IsDigit c          return value      or if you want to be a little more fancy  public Boolean IsNumber String value      return value All Char IsDigit       update 2   from  stackonfire to deal with null or empty strings   public Boolean IsNumber String s         Boolean value   true       if  s    String Empty    s    null             value false         else            foreach Char c in s ToCharArray                   value   value  amp  amp  Char IsDigit c                     return value

User · Answer

I know this has been answered in many different ways  with extensions and lambda examples  but a combination of both for the simplest solution   public static bool IsNumeric this String s        return s All Char IsDigit       or if you are using Visual Studio 2015  C  6 0 or greater  then  public static bool IsNumeric this String s    gt  s All Char IsDigit     Awesome C 6 on one line   Of course this is limited because it just tests for only numeric characters     To use  just have a string and call the method on it  such as   bool IsaNumber    123456  IsNumeric

User · Answer

In addition to the previous correct answers it is probably worth pointing out that  Not a Number   NaN  in its general usage is not equivalent to a string that cannot be evaluated as a numeric value  NaN is usually understood as a numeric value used to represent the result of an  impossible  calculation - where the result is undefined  In this respect I would say the Javascript usage is slightly misleading  In C  NaN is defined as a property of the single and double numeric types and is used to refer explicitly to the result of diving zero by zero  Other languages use it to represent different  impossible  values

User · Answer

Simple extension   public static bool IsNumeric this String str        try               Double Parse str ToString             return true            catch             return false

User · Answer

I was using Chris Lively s snippet  selected answer  encapsulated in a bool function like Gishu s suggestion for a year or two   I used it to make sure certain query strings were only numeric before proceeding with further processing   I started getting some errant querystrings that the marked answer was not handling  specifically  whenever a comma was passed after a number like  3645    returned true    This is the resulting mod      static public bool IsNumeric string s             double myNum   0        if  Double TryParse s  out myNum                    if  s Contains       return false           return true                else                  return false

User · Answer

Actually  Double NaN is supported in all  NET versions 2 0 and greater

User · Answer

VB has the IsNumeric function  You could reference Microsoft VisualBasic dll and use it

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