How to parse a string into a nullable int

Question

I m wanting to parse a string into a nullable int in C    ie  I want to get back either the int value of the string or null if it can t be parsed   I was kind of hoping that this would work  int  val   stringVal as int     But that won t work  so the way I m doing it now is I ve written this extension method  public static int  ParseNullableInt this string value        if  value    null    value Trim      string Empty                return null            else               try                       return int Parse value                     catch                       return null                         Is there a better way of doing this   EDIT   Thanks for the TryParse suggestions  I did know about that  but it worked out about the same   I m more interested in knowing if there is a built-in framework method that will parse directly into a nullable int

User · Answer

I realise this is an old topic  but can t you simply    Nullable lt int gt  int Parse stringVal

User · Answer

Old topic  but how about   public static int  ParseToNullableInt this string value         return String IsNullOrEmpty value    null    int Parse value  as int        I like this better as the requriement where to parse null  the TryParse version would not throw an error on e g  ToNullableInt32 XXX   That may introduce unwanted silent errors

User · Answer

I found and adapted some code for a Generic NullableParser class   The full code is on my blog Nullable TryParse  using System  using System Collections Generic  using System Linq  using System Text  using System Globalization  namespace SomeNamespace            lt summary gt          A parser for nullable types  Will return null when parsing fails           lt  summary gt           lt typeparam name  T  gt  lt  typeparam gt              public static class NullableParser lt T gt  where T   struct               public delegate bool TryParseDelegate string s  out T result                lt summary gt              A generic Nullable Parser  Supports parsing of all types that implements the tryParse method               lt  summary gt               lt param name  text  gt Text to be parsed lt  param gt               lt param name  result  gt Value is true for parse succeeded lt  param gt               lt returns gt bool lt  returns gt          public static bool TryParse string s  out Nullable lt T gt  result                        bool success   false              try                               if  string IsNullOrEmpty s                                         result   null                      success   true                                    else                                       IConvertible convertableString   s as IConvertible                      if  convertableString    null                                                result   new Nullable lt T gt   T convertableString ToType typeof T                               CultureInfo CurrentCulture                            success   true                                            else                                               success   false                          result   null                                                                    catch                               success   false                  result   null                            return success

User · Answer

This solution is generic without reflection overhead   public static Nullable lt T gt  ParseNullable lt T gt  string s  Func lt string  T gt  parser  where T   struct       if  string IsNullOrEmpty s     string IsNullOrEmpty s Trim     return null      else return parser s      static void Main string   args        Nullable lt int gt  i   ParseNullable  -1   int Parse       Nullable lt float gt  dt   ParseNullable  3 14   float Parse

User · Answer

C   lt  7 1 using default operator var result   int TryParse foo  out var f    f   default int     C   gt   7 1 using default literal var result   int TryParse foo  out var f    f   default   See C  language versioning to ascertain what language version your project supports Sources   var Int32 TryParse conditional operator default operator  explained in this stackoverflow post   nullable value type

User · Answer

I ve come up with this one  which has satisfied my requirements  I wanted my extension method to emulate as close as possible the return of the framework s TryParse  but without try   catch   blocks and without the compiler complaining about inferring a nullable type within the framework method   private static bool TryParseNullableInt this string s  out int  result        int i      result   int TryParse s  out i     int  i   null      return result    null

User · Answer

Using delegates  the following code is able to provide reusability if you find yourself needing the nullable parsing for more than one structure type  I ve shown both the  Parse   and  TryParse   versions here   This is an example usage   NullableParser TryParseInt ViewState  Id   as string     And here is the code that gets you there     public class NullableParser         public delegate T ParseDelegate lt T gt  string input  where T   struct      public delegate bool TryParseDelegate lt T gt  string input  out T outtie  where T   struct      private static T  Parse lt T gt  string input  ParseDelegate lt T gt  DelegateTheParse  where T   struct             if  string IsNullOrEmpty input   return null        return DelegateTheParse input             private static T  TryParse lt T gt  string input  TryParseDelegate lt T gt  DelegateTheTryParse  where T   struct             T x        if  DelegateTheTryParse input  out x   return x        return null            public static int  ParseInt string input              return Parse lt int gt  input  new ParseDelegate lt int gt  int Parse              public static int  TryParseInt string input              return TryParse lt int gt  input  new TryParseDelegate lt int gt  int TryParse              public static bool  TryParseBool string input              return TryParse lt bool gt  input  new TryParseDelegate lt bool gt  bool TryParse              public static DateTime  TryParseDateTime string input              return TryParse lt DateTime gt  input  new TryParseDelegate lt DateTime gt  DateTime TryParse

User · Answer

Glenn Slaven  I m more interested in knowing if   there is a built-in framework method   that will parse directly into a   nullable int    There is this approach that will parse directly to a nullable int  and not just int  if the value is valid like null or empty string  but does throw an exception for invalid values so you will need to catch the exception and return the default value for those situations   public static T Parse lt T gt  object value        try   return  T System ComponentModel TypeDescriptor GetConverter typeof T   ConvertFrom value ToString           catch   return default T         This approach can still be used for non-nullable parses as well as nullable   enum Fruit   Orange  Apple   var res1   Parse lt Fruit gt   Apple    var res2   Parse lt Fruit  gt   Banana    var res3   Parse lt int  gt   100      5    use this for non-zero default var res4   Parse lt Unit gt   45       NB  There is an IsValid method on the converter you can use instead of capturing the exception  thrown exceptions does result in unnecessary overhead if expected   Unfortunately it only works since  NET 4 but there s still an issue where it doesn t check your locale when validating correct DateTime formats  see bug 93559

User · Answer

The following should work for any struct type  It is based off code by Matt Manela from MSDN forums  As Murph points out the exception handling could be expensive compared to using the Types dedicated TryParse method           public static bool TryParseStruct lt T gt  this string value  out Nullable lt T gt  result              where T  struct                        if  string IsNullOrEmpty value                                 result   new Nullable lt T gt                      return true                             result   default T               try                               IConvertible convertibleString    IConvertible value                  result   new Nullable lt T gt   T convertibleString ToType typeof T   System Globalization CultureInfo CurrentCulture                              catch InvalidCastException                                return false                            catch  FormatException                                return false                            return true              These were the basic test cases I used           string parseOne    1           int  resultOne          bool successOne   parseOne TryParseStruct lt int gt  out resultOne           Assert IsTrue successOne           Assert AreEqual 1  resultOne            string parseEmpty   string Empty          int  resultEmpty          bool successEmpty   parseEmpty TryParseStruct lt int gt  out resultEmpty           Assert IsTrue successEmpty           Assert IsFalse resultEmpty HasValue            string parseNull   null          int  resultNull          bool successNull   parseNull TryParseStruct lt int gt  out resultNull           Assert IsTrue successNull           Assert IsFalse resultNull HasValue            string parseInvalid    FooBar           int  resultInvalid          bool successInvalid   parseInvalid TryParseStruct lt int gt  out resultInvalid           Assert IsFalse successInvalid

User · Answer

I feel my solution is a very clean and nice solution   public static T  NullableParse lt T gt  string s  where T   struct       try               return  T typeof T  GetMethod  Parse   new    typeof string    Invoke null  new     s               catch  Exception                return null            This is of course a generic solution which only require that the generics argument has a static method  Parse string     This works for numbers  boolean  DateTime  etc

User · Answer

I would suggest following extension methods for string parsing into int value with ability to define default value in case parsing is not possible   public static int ParseInt this string value  int defaultIntValue   0                        return int TryParse value  out var parsedInt    parsedInt   defaultIntValue             public static int  ParseNullableInt this string value                        if  string IsNullOrEmpty value                   return null               return value ParseInt

User · Answer

public static void Main string   args                 var myString    abc            int  myInt   ParseOnlyInt myString              null          myString    1234            myInt   ParseOnlyInt myString              1234           private static int  ParseOnlyInt string s                return int TryParse s  out var i    i    int  null

User · Answer

You can forget all other answers - there is a great generic solution  http   cleansharp de wordpress 2011 05 generischer-typeconverter   This allows you to write very clean code like this   string value   null  int  x   value ConvertOrDefault      and also   object obj   1     string value   null  int x   5  if  value TryConvert out x       Console WriteLine  TryConvert example      x     bool boolean    false  ConvertOrDefault    bool  nullableBoolean      ConvertOrDefault    int integer   obj ConvertOrDefault    int negativeInteger    -12123  ConvertOrDefault    int  nullableInteger   value ConvertOrDefault    MyEnum enumValue    SecondValue  ConvertOrDefault     MyObjectBase myObject   new MyObjectClassA    MyObjectClassA myObjectClassA   myObject ConvertOrDefault

User · Answer

I suggest code bellow  You may work with exception  when convert error occured   public static class Utils         public static bool TryParse lt Tin  Tout gt  this Tin obj  Func lt Tin  Tout gt  onConvert  Action lt Tout gt  onFill  Action lt Exception gt  onError      Tout value   default Tout     bool ret   true    try       value   onConvert obj         catch  Exception exc        onError exc       ret   false        if  ret      onFill value     return ret     public static bool TryParse this string str  Action lt int  gt  onFill  Action lt Exception gt  onError      return Utils TryParse str       s   gt  string IsNullOrEmpty s    null    int  int Parse s        onFill       onError     public static bool TryParse this string str  Action lt int gt  onFill  Action lt Exception gt  onError      return Utils TryParse str       s   gt  int Parse s        onFill       onError         Use this extension method in code  fill int  Age property of a person class    string ageStr   AgeTextBox Text  Utils TryParse ageStr  i   gt  person Age   i  exc   gt    MessageBox Show exc Message         OR  AgeTextBox Text TryParse i   gt  person Age   i  exc   gt    MessageBox Show exc Message

User · Answer

I felt I should share mine which is a bit more generic   Usage   var result    123  ParseBy int Parse    var result2    123  ParseBy lt int gt  int TryParse     Solution   public static class NullableParse       public static Nullable lt T gt  ParseBy lt T gt  this string input  Func lt string  T gt  parser          where T   struct               try                       return parser input                     catch  Exception exc                        return null                       public delegate bool TryParseDelegate lt T gt  string input  out T result        public static Nullable lt T gt  ParseBy lt T gt  this string input  TryParseDelegate lt T gt  parser          where T   struct               T t          if  parser input  out t   return t          return null            First version is a slower since it requires a try-catch but it looks cleaner  If it won t be called many times with invalid strings  it is not that important  If performance is an issue  please note that when using TryParse methods  you need to specify the type parameter of ParseBy as it can not be inferred by the compiler  I also had to define a delegate as out keyword can not be used within Func lt    but at least this time compiler does not require an explicit instance   Finally  you can use it with other structs as well  i e  decimal  DateTime  Guid  etc

User · Answer

Updated to use modern C  as per  sblom s suggestion   I had this problem and I ended up with this  after all  an if and 2 returns is soo long-winded     int  ToNullableInt  string val        gt  int TryParse  val  out var i     int   i   null    On a more serious note  try not to mix int  which is a C  keyword  with Int32  which is a  NET Framework BCL type - although it works  it just makes code look messy

User · Answer

You should never use an exception if you don t have to - the overhead is horrible   The variations on TryParse solve the problem - if you want to get creative  to make your code look more elegant  you could probably do something with an extension method in 3 5 but the code would be more or less the same

User · Answer

You can do this in one line  using the conditional operator and the fact that you can cast null to a nullable type  two lines  if you don t have a pre-existing int you can reuse for the output of TryParse    Pre C 7   int tempVal  int  val   Int32 TryParse stringVal  out tempVal    Int32 Parse stringVal     int  null    With C 7 s updated syntax that allows you to declare an output variable in the method call  this gets even simpler   int  val   Int32 TryParse stringVal  out var tempVal    tempVal    int  null

User · Answer

Try this   public static int  ParseNullableInt this string value        int intValue      if  int TryParse value  out intValue           return intValue      return null

User · Answer

int TryParse is probably a tad easier   public static int  ToNullableInt this string s        int i      if  int TryParse s  out i   return i      return null      Edit  Glenn int TryParse is  built into the framework   It and int Parse are the way to parse strings to ints

User · Answer

I m more interested in knowing if there is a built-in framework method that will parse directly into a nullable int    There isn t

[c#] How to parse a string into a nullable int

Examples related to c#

Examples related to .net

Examples related to string

Examples related to .net-3.5

Examples related to nullable