System.Object.ToString method

Object.ToString is a common formatting method in .NET. It converts an object to its string representation so that it is suitable for display. (For information about formatting support in .NET, see Formatting Types.) Default implementations of the Object.ToString method return the fully qualified name of the object's type.

Types frequently override the Object.ToString method to provide a more suitable string representation of a particular type. Types also frequently overload the Object.ToString method to provide support for format strings or culture-sensitive formatting.

The default Object.ToString() method

The default implementation of the ToString method returns the fully qualified name of the type of the Object, as the following example shows.

Object obj = new Object();
Console.WriteLine(obj.ToString());

// The example displays the following output:
// System.Object

let obj = obj ()
printfn $"{obj.ToString()}"
// printfn $"{obj}" // Equivalent

// The example displays the following output:
// System.Object

Module Example3
 Public Sub Main()
 Dim obj As New Object()
 Console.WriteLine(obj.ToString())
 End Sub
End Module
' The example displays the following output:
' System.Object

Because Object is the base class of all reference types in .NET, this behavior is inherited by reference types that do not override the ToString method. The following example illustrates this. It defines a class named Object1 that accepts the default implementation of all Object members. Its ToString method returns the object's fully qualified type name.

using System;
using Examples;

namespace Examples
{
 public class Object1
 {
 }
}

public class Example5
{
 public static void Main()
 {
 object obj1 = new Object1();
 Console.WriteLine(obj1.ToString());
 }
}
// The example displays the following output:
// Examples.Object1

type Object1() = class end

let obj1 = Object1()
printfn $"{obj1.ToString()}"
// The example displays the following output:
// Examples.Object1

Public Class Object1
End Class

Module Example4
 Public Sub Main()
 Dim obj1 As New Object1()
 Console.WriteLine(obj1.ToString())
 End Sub
End Module
' The example displays the following output:
' Examples.Object1

Override the Object.ToString() method

Types commonly override the Object.ToString method to return a string that represents the object instance. For example, the base types such as Char, Int32, and String provide ToString implementations that return the string form of the value that the object represents. The following example defines a class, Object2, that overrides the ToString method to return the type name along with its value.

using System;

public class Object2
{
 private object value;

 public Object2(object value)
 {
 this.value = value;
 }

 public override string ToString()
 {
 return base.ToString() + ": " + value.ToString();
 }
}

public class Example6
{
 public static void Main()
 {
 Object2 obj2 = new Object2('a');
 Console.WriteLine(obj2.ToString());
 }
}
// The example displays the following output:
// Object2: a

type Object2(value: obj) =
 inherit obj ()
 override _.ToString() =
 base.ToString() + ": " + value.ToString()

let obj2 = Object2 'a'
printfn $"{obj2.ToString()}"
// The example displays the following output:
// Object2: a

Public Class Object2
 Private value As Object
 
 Public Sub New(value As Object)
 Me.value = value
 End Sub
 
 Public Overrides Function ToString() As String
 Return MyBase.ToString + ": " + value.ToString()
 End Function
End Class

Module Example5
 Public Sub Main()
 Dim obj2 As New Object2("a"c)
 Console.WriteLine(obj2.ToString())
 End Sub
End Module
' The example displays the following output:
' Object2: a

The following table lists the type categories in .NET and indicates whether or not they override the Object.ToString method.

See the Notes to Inheritors section for additional information on overriding ToString.

Overload the ToString method

In addition to overriding the parameterless Object.ToString() method, many types overload the ToString method to provide versions of the method that accept parameters. Most commonly, this is done to provide support for variable formatting and culture-sensitive formatting.

The following example overloads the ToString method to return a result string that includes the value of various fields of an Automobile class. It defines four format strings: G, which returns the model name and year; D, which returns the model name, year, and number of doors; C, which returns the model name, year, and number of cylinders; and A, which returns a string with all four field values.

using System;

public class Automobile
{
 private int _doors;
 private string _cylinders;
 private int _year;
 private string _model;

 public Automobile(string model, int year , int doors,
 string cylinders)
 {
 _model = model;
 _year = year;
 _doors = doors;
 _cylinders = cylinders;
 }

 public int Doors
 { get { return _doors; } }

 public string Model
 { get { return _model; } }

 public int Year
 { get { return _year; } }

 public string Cylinders
 { get { return _cylinders; } }

 public override string ToString()
 {
 return ToString("G");
 }

 public string ToString(string fmt)
 {
 if (string.IsNullOrEmpty(fmt))
 fmt = "G";

 switch (fmt.ToUpperInvariant())
 {
 case "G":
 return string.Format("{0} {1}", _year, _model);
 case "D":
 return string.Format("{0} {1}, {2} dr.",
 _year, _model, _doors);
 case "C":
 return string.Format("{0} {1}, {2}",
 _year, _model, _cylinders);
 case "A":
 return string.Format("{0} {1}, {2} dr. {3}",
 _year, _model, _doors, _cylinders);
 default:
 string msg = string.Format("'{0}' is an invalid format string",
 fmt);
 throw new ArgumentException(msg);
 }
 }
}

public class Example7
{
 public static void Main()
 {
 var auto = new Automobile("Lynx", 2016, 4, "V8");
 Console.WriteLine(auto.ToString());
 Console.WriteLine(auto.ToString("A"));
 }
}
// The example displays the following output:
// 2016 Lynx
// 2016 Lynx, 4 dr. V8

open System

type Automobile(model: string, year: int, doors: int, cylinders: string) =
 member _.Doors = doors
 member _.Model = model
 member _.Year = year
 member _.Cylinders = cylinders

 override this.ToString() =
 this.ToString "G"

 member _.ToString(fmt) =
 let fmt = 
 if String.IsNullOrEmpty fmt then "G"
 else fmt.ToUpperInvariant()

 match fmt with
 | "G" ->
 $"{year} {model}"
 | "D" ->
 $"{year} {model}, {doors} dr."
 | "C" ->
 $"{year} {model}, {cylinders}"
 | "A" ->
 $"{year} {model}, {doors} dr. {cylinders}"
 | _ ->
 raise (ArgumentException $"'{fmt}' is an invalid format string")

let auto = Automobile("Lynx", 2016, 4, "V8")
printfn $"{auto}"
printfn $"""{auto.ToString "A"}"""
// The example displays the following output:
// 2016 Lynx
// 2016 Lynx, 4 dr. V8

Public Class Automobile
 Private _doors As Integer
 Private _cylinders As String
 Private _year As Integer
 Private _model As String
 
 Public Sub New(model As String, year As Integer, doors As Integer,
 cylinders As String)
 _model = model
 _year = year
 _doors = doors
 _cylinders = cylinders
 End Sub
 
 Public ReadOnly Property Doors As Integer
 Get
 Return _doors
 End Get
 End Property
 
 Public ReadOnly Property Model As String
 Get
 Return _model
 End Get
 End Property
 
 Public ReadOnly Property Year As Integer
 Get
 Return _year
 End Get
 End Property
 
 Public ReadOnly Property Cylinders As String
 Get
 Return _cylinders
 End Get
 End Property
 
 Public Overrides Function ToString() As String
 Return ToString("G")
 End Function
 
 Public Overloads Function ToString(fmt As String) As String
 If String.IsNullOrEmpty(fmt) Then fmt = "G"
 
 Select Case fmt.ToUpperInvariant()
 Case "G"
 Return String.Format("{0} {1}", _year, _model)
 Case "D"
 Return String.Format("{0} {1}, {2} dr.",
 _year, _model, _doors)
 Case "C"
 Return String.Format("{0} {1}, {2}",
 _year, _model, _cylinders)
 Case "A"
 Return String.Format("{0} {1}, {2} dr. {3}",
 _year, _model, _doors, _cylinders)
 Case Else
 Dim msg As String = String.Format("'{0}' is an invalid format string",
 fmt)
 Throw New ArgumentException(msg)
 End Select
 End Function
End Class

Module Example6
 Public Sub Main()
 Dim auto As New Automobile("Lynx", 2016, 4, "V8")
 Console.WriteLine(auto.ToString())
 Console.WriteLine(auto.ToString("A"))
 End Sub
End Module
' The example displays the following output:
' 2016 Lynx
' 2016 Lynx, 4 dr. V8

The following example calls the overloaded Decimal.ToString(String, IFormatProvider) method to display culture-sensitive formatting of a currency value.

using System;
using System.Globalization;

public class Example8
{
 public static void Main()
 {
 string[] cultureNames = { "en-US", "en-GB", "fr-FR",
 "hr-HR", "ja-JP" };
 Decimal value = 1603.49m;
 foreach (var cultureName in cultureNames) {
 CultureInfo culture = new CultureInfo(cultureName);
 Console.WriteLine($"{culture.Name}: {value.ToString("C2", culture)}");
 }
 }
}
// The example displays the following output:
// en-US: $1,603.49
// en-GB: £1,603.49
// fr-FR: 1 603,49 €
// hr-HR: 1.603,49 kn
// ja-JP: ¥1,603.49

open System.Globalization

let cultureNames =
 [| "en-US"; "en-GB"; "fr-FR"; "hr-HR"; "ja-JP" |]
let value = 1603.49m
for cultureName in cultureNames do
 let culture = CultureInfo cultureName
 printfn $"""{culture.Name}: {value.ToString("C2", culture)}"""
// The example displays the following output:
// en-US: $1,603.49
// en-GB: £1,603.49
// fr-FR: 1 603,49 €
// hr-HR: 1.603,49 kn
// ja-JP: ¥1,603.49

Imports System.Globalization

Module Example7
 Public Sub Main()
 Dim cultureNames() As String = {"en-US", "en-GB", "fr-FR",
 "hr-HR", "ja-JP"}
 Dim value As Decimal = 1603.49D
 For Each cultureName In cultureNames
 Dim culture As New CultureInfo(cultureName)
 Console.WriteLine("{0}: {1}", culture.Name,
 value.ToString("C2", culture))
 Next
 End Sub
End Module
' The example displays the following output:
' en-US: $1,603.49
' en-GB: £1,603.49
' fr-FR: 1 603,49 €
' hr-HR: 1.603,49 kn
' ja-JP: ¥1,603.49

For more information on format strings and culture-sensitive formatting, see Formatting Types. For the format strings supported by numeric values, see Standard Numeric Format Strings and Custom Numeric Format Strings. For the format strings supported by date and time values, see Standard Date and Time Format Strings and Custom Date and Time Format Strings.

Extend the Object.ToString method

Because a type inherits the default Object.ToString method, you may find its behavior undesirable and want to change it. This is particularly true of arrays and collection classes. While you may expect the ToString method of an array or collection class to display the values of its members, it instead displays the type fully qualified type name, as the following example shows.

int[] values = { 1, 2, 4, 8, 16, 32, 64, 128 };
Console.WriteLine(values.ToString());

List<int> list = new List<int>(values);
Console.WriteLine(list.ToString());

// The example displays the following output:
// System.Int32[]
// System.Collections.Generic.List`1[System.Int32]

let values = [| 1; 2; 4; 8; 16; 32; 64; 128 |]
printfn $"{values}"

let list = ResizeArray values
printfn $"{list}"

// The example displays the following output:
// System.Int32[]
// System.Collections.Generic.List`1[System.Int32]

Imports System.Collections.Generic

Module Example
 Public Sub Main()
 Dim values() As Integer = { 1, 2, 4, 8, 16, 32, 64, 128 }
 Console.WriteLine(values.ToString())
 
 Dim list As New List(Of Integer)(values)
 Console.WriteLine(list.ToString())
 End Sub
End Module
' The example displays the following output:
' System.Int32[]
' System.Collections.Generic.List`1[System.Int32]

You have several options to produce the result string that you'd like.

• If the type is an array, a collection object, or an object that implements the IEnumerable or IEnumerable<T> interfaces, you can enumerate its elements by using the foreach statement in C# or the For Each...Next construct in Visual Basic.

• If the class is not sealed (in C#) or NotInheritable (in Visual Basic), you can develop a wrapper class that inherits from the base class whose Object.ToString method you want to customize. At a minimum, this requires that you do the following:

  1. Implement any necessary constructors. Derived classes do not inherit their base class constructors.
  2. Override the Object.ToString method to return the result string that you'd like.

  The following example defines a wrapper class for the List<T> class. It overrides the Object.ToString method to display the value of each method of the collection rather than the fully qualified type name.

  using System;
  using System.Collections.Generic;
  
  public class CList<T> : List<T>
  {
   public CList(IEnumerable<T> collection) : base(collection)
   { }
  
   public CList() : base()
   {}
  
   public override string ToString()
   {
   string retVal = string.Empty;
   foreach (T item in this) {
   if (string.IsNullOrEmpty(retVal))
   retVal += item.ToString();
   else
   retVal += string.Format(", {0}", item);
   }
   return retVal;
   }
  }
  
  public class Example2
  {
   public static void Main()
   {
   var list2 = new CList<int>();
   list2.Add(1000);
   list2.Add(2000);
   Console.WriteLine(list2.ToString());
   }
  }
  // The example displays the following output:
  // 1000, 2000
  

  open System
  open System.Collections.Generic
  
  type CList<'T>() = 
   inherit ResizeArray<'T>()
   
   override this.ToString() =
   let mutable retVal = String.Empty
   for item in this do
   if String.IsNullOrEmpty retVal then
   retVal <- retVal + string item
   else
   retVal <- retVal + $", {item}"
   retVal
  
  let list2 = CList()
  list2.Add 1000
  list2.Add 2000
  printfn $"{list2}"
  // The example displays the following output:
  // 1000, 2000
  

  Imports System.Collections.Generic
  
  Public Class CList(Of T) : Inherits List(Of T)
   Public Sub New(capacity As Integer)
   MyBase.New(capacity)
   End Sub
  
   Public Sub New(collection As IEnumerable(Of T))
   MyBase.New(collection)
   End Sub
  
   Public Sub New()
   MyBase.New()
   End Sub
  
   Public Overrides Function ToString() As String
   Dim retVal As String = String.Empty
   For Each item As T In Me
   If String.IsNullOrEmpty(retval) Then
   retVal += item.ToString()
   Else
   retval += String.Format(", {0}", item)
   End If
   Next
   Return retVal
   End Function
  End Class
  
  Module Example1
   Public Sub Main()
   Dim list2 As New CList(Of Integer)
   list2.Add(1000)
   list2.Add(2000)
   Console.WriteLine(list2.ToString())
   End Sub
  End Module
  ' The example displays the following output:
  ' 1000, 2000
  

• Develop an extension method that returns the result string that you want. Note that you can't override the default Object.ToString method in this way—that is, your extension class (in C#) or module (in Visual Basic) cannot have a parameterless method named ToString that's called in place of the original type's ToString method. You'll have to provide some other name for your parameterless ToString replacement.

  The following example defines two methods that extend the List<T> class: a parameterless ToString2 method, and a ToString method with a String parameter that represents a format string.

  using System;
  using System.Collections.Generic;
  
  public static class StringExtensions
  {
   public static string ToString2<T>(this List<T> l)
   {
   string retVal = string.Empty;
   foreach (T item in l)
   retVal += string.Format("{0}{1}", string.IsNullOrEmpty(retVal) ?
   "" : ", ",
   item);
   return string.IsNullOrEmpty(retVal) ? "{}" : "{ " + retVal + " }";
   }
  
   public static string ToString<T>(this List<T> l, string fmt)
   {
   string retVal = string.Empty;
   foreach (T item in l) {
   IFormattable ifmt = item as IFormattable;
   if (ifmt != null)
   retVal += string.Format("{0}{1}",
   string.IsNullOrEmpty(retVal) ?
   "" : ", ", ifmt.ToString(fmt, null));
   else
   retVal += ToString2(l);
   }
   return string.IsNullOrEmpty(retVal) ? "{}" : "{ " + retVal + " }";
   }
  }
  
  public class Example3
  {
   public static void Main()
   {
   List<int> list = new List<int>();
   list.Add(1000);
   list.Add(2000);
   Console.WriteLine(list.ToString2());
   Console.WriteLine(list.ToString("N0"));
   }
  }
  // The example displays the following output:
  // { 1000, 2000 }
  // { 1,000, 2,000 }
  

  open System
  open System.Collections.Generic
  
  type List<'T> with
   member this.ToString2<'T>() = 
   let mutable retVal = String.Empty
   for item in this do
   retVal <- retVal + $"""{if String.IsNullOrEmpty retVal then "" else ", "}{item}"""
   if String.IsNullOrEmpty retVal then "{}" else "{ " + retVal + " }"
  
   member this.ToString<'T>(fmt: string) =
   let mutable retVal = String.Empty
   for item in this do
   match box item with
   | :? IFormattable as ifmt ->
   retVal <- retVal + $"""{if String.IsNullOrEmpty retVal then "" else ", "}{ifmt.ToString(fmt, null)}"""
   | _ ->
   retVal <- retVal + this.ToString2()
   if String.IsNullOrEmpty retVal then "{}" else "{ " + retVal + " }"
  
  let list = ResizeArray()
  list.Add 1000
  list.Add 2000
  printfn $"{list.ToString2()}"
  printfn $"""{list.ToString "N0"}"""
  // The example displays the following output:
  // { 1000, 2000 }
  // { 1,000, 2,000 }
  

  Imports System.Collections.Generic
  Imports System.Runtime.CompilerServices
  
  Public Module StringExtensions
   <Extension()>
   Public Function ToString2(Of T)(l As List(Of T)) As String
   Dim retVal As String = ""
   For Each item As T In l
   retVal += String.Format("{0}{1}", If(String.IsNullOrEmpty(retVal),
   "", ", "),
   item)
   Next
   Return If(String.IsNullOrEmpty(retVal), "{}", "{ " + retVal + " }")
   End Function
  
   <Extension()>
   Public Function ToString(Of T)(l As List(Of T), fmt As String) As String
   Dim retVal As String = String.Empty
   For Each item In l
   Dim ifmt As IFormattable = TryCast(item, IFormattable)
   If ifmt IsNot Nothing Then
   retVal += String.Format("{0}{1}",
   If(String.IsNullOrEmpty(retval),
   "", ", "), ifmt.ToString(fmt, Nothing))
   Else
   retVal += ToString2(l)
   End If
   Next
   Return If(String.IsNullOrEmpty(retVal), "{}", "{ " + retVal + " }")
   End Function
  End Module
  
  Module Example2
   Public Sub Main()
   Dim list As New List(Of Integer)
   list.Add(1000)
   list.Add(2000)
   Console.WriteLine(list.ToString2())
   Console.WriteLine(list.ToString("N0"))
   End Sub
  End Module
  ' The example displays the following output:
  ' { 1000, 2000 }
  ' { 1,000, 2,000 }
  

Notes for the Windows Runtime

When you call the ToString method on a class in the Windows Runtime, it provides the default behavior for classes that don't override ToString. This is part of the support that .NET provides for the Windows Runtime (see .NET Support for Windows Store Apps and Windows Runtime). Classes in the Windows Runtime don't inherit Object, and don't always implement a ToString. However, they always appear to have ToString, Equals(Object), and GetHashCode methods when you use them in your C# or Visual Basic code, and .NET provides a default behavior for these methods.

The common language runtime uses IStringable.ToString on a Windows Runtime object before falling back to the default implementation of Object.ToString.

The Windows Runtime and the IStringable Interface

The Windows Runtime includes an IStringable interface whose single method, IStringable.ToString, provides basic formatting support comparable to that provided by Object.ToString. To prevent ambiguity, you should not implement IStringable on managed types.

When managed objects are called by native code or by code written in languages such as JavaScript or C++/CX, they appear to implement IStringable. The common language runtime automatically routes calls from IStringable.ToString to Object.ToString if IStringable is not implemented on the managed object.

If you do choose to implement IStringable in a public managed type that's exported in a Windows Runtime component, the following restrictions apply:

• You can define the IStringable interface only in a "class implements" relationship, as follows:

  public class NewClass : IStringable
  

  Public Class NewClass : Implements IStringable
  

• You cannot implement IStringable on an interface.

• You cannot declare a parameter to be of type IStringable.

• IStringable cannot be the return type of a method, property, or field.

• You cannot hide your IStringable implementation from base classes by using a method definition such as the following:

  public class NewClass : IStringable
  {
   public new string ToString()
   {
   return "New ToString in NewClass";
   }
  }
  

  Instead, the IStringable.ToString implementation must always override the base class implementation. You can hide a ToString implementation only by invoking it on a strongly typed class instance.

Under a variety of conditions, calls from native code to a managed type that implements IStringable or hides its ToString implementation can produce unexpected behavior.