Boolean Structure
Represents a Boolean (true or false) value.
Assembly: mscorlib (in mscorlib.dll)
| Name | Description | |
|---|---|---|
![]() | CompareTo(Boolean) | Compares this instance to a specified Boolean object and returns an integer that indicates their relationship to one another. |
![]() | CompareTo(Object) | Compares this instance to a specified object and returns an integer that indicates their relationship to one another. |
![]() | Equals(Boolean) | Returns a value indicating whether this instance is equal to a specified Boolean object. |
![]() | Equals(Object) | Returns a value indicating whether this instance is equal to a specified object.(Overrides ValueType.Equals(Object).) |
![]() | GetHashCode() | Returns the hash code for this instance.(Overrides ValueType.GetHashCode().) |
![]() | GetType() | |
![]() | GetTypeCode() | Returns the type code for the Boolean value type. |
![]() ![]() | Parse(String) | Converts the specified string representation of a logical value to its Boolean equivalent. |
![]() | ToString() | Converts the value of this instance to its equivalent string representation (either "True" or "False").(Overrides ValueType.ToString().) |
![]() | ToString(IFormatProvider) | Converts the value of this instance to its equivalent string representation (either "True" or "False"). |
![]() ![]() | TryParse(String, Boolean) |
| Name | Description | |
|---|---|---|
![]() ![]() | FalseString | Represents the Boolean value false as a string. This field is read-only. |
![]() ![]() | TrueString | Represents the Boolean value true as a string. This field is read-only. |
| Name | Description | |
|---|---|---|
![]() ![]() | IConvertible.ToBoolean(IFormatProvider) | This API supports the product infrastructure and is not intended to be used directly from your code. For a description of this member, see IConvertible.ToBoolean. |
![]() ![]() | IConvertible.ToByte(IFormatProvider) | This API supports the product infrastructure and is not intended to be used directly from your code. For a description of this member, see IConvertible.ToByte. |
![]() ![]() | IConvertible.ToChar(IFormatProvider) | This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to use this method throws an InvalidCastException. |
![]() ![]() | IConvertible.ToDateTime(IFormatProvider) | This API supports the product infrastructure and is not intended to be used directly from your code. This conversion is not supported. Attempting to use this method throws an InvalidCastException. |
![]() ![]() | IConvertible.ToDecimal(IFormatProvider) | This API supports the product infrastructure and is not intended to be used directly from your code. For a description of this member, see IConvertible.ToDecimal.. |
![]() ![]() | IConvertible.ToDouble(IFormatProvider) | This API supports the product infrastructure and is not intended to be used directly from your code. For a description of this member, see IConvertible.ToDouble.. |
![]() ![]() | IConvertible.ToInt16(IFormatProvider) | This API supports the product infrastructure and is not intended to be used directly from your code. For a description of this member, see IConvertible.ToInt16. |
![]() ![]() | IConvertible.ToInt32(IFormatProvider) | This API supports the product infrastructure and is not intended to be used directly from your code. For a description of this member, see IConvertible.ToInt32. |
![]() ![]() | IConvertible.ToInt64(IFormatProvider) | This API supports the product infrastructure and is not intended to be used directly from your code. For a description of this member, see IConvertible.ToInt64. |
![]() ![]() | IConvertible.ToSByte(IFormatProvider) | This API supports the product infrastructure and is not intended to be used directly from your code. For a description of this member, see IConvertible.ToSByte. |
![]() ![]() | IConvertible.ToSingle(IFormatProvider) | This API supports the product infrastructure and is not intended to be used directly from your code. For a description of this member, see IConvertible.ToSingle.. |
![]() ![]() | IConvertible.ToType(Type, IFormatProvider) | This API supports the product infrastructure and is not intended to be used directly from your code. For a description of this member, see IConvertible.ToType. |
![]() ![]() | IConvertible.ToUInt16(IFormatProvider) | This API supports the product infrastructure and is not intended to be used directly from your code. For a description of this member, see IConvertible.ToUInt16. |
![]() ![]() | IConvertible.ToUInt32(IFormatProvider) | This API supports the product infrastructure and is not intended to be used directly from your code. For a description of this member, see IConvertible.ToUInt32. |
![]() ![]() | IConvertible.ToUInt64(IFormatProvider) | This API supports the product infrastructure and is not intended to be used directly from your code. For a description of this member, see IConvertible.ToUInt64. |
A Boolean instance can have either of two values: true, or false.
The Boolean structure provides methods that support the following tasks:
Converting Boolean values to strings: ToString
Parsing strings to convert them to Boolean values: Parse and TryParse
The following sections explain these tasks and other usage details:
Formatting Boolean values
Converting to and from Boolean values
Parsing Boolean values
Comparing Boolean values
Working with Booleans as binary values
Performing operations with Boolean values
Booleans and Interop
The string representation of a Boolean is either "True" for a true value or "False" for a false value. The string representation of a Boolean value is defined by the read-only TrueString and FalseString fields.
You use the ToString method to convert Boolean values to strings. The Boolean structure includes two ToString overloads: the parameterless ToString() method and the ToString(IFormatProvider) method, which includes a parameter that controls formatting. However, because this parameter is ignored, the two overloads produce identical strings. The ToString(IFormatProvider) method does not support culture-sensitive formatting.
The following example illustrates formatting with the ToString method. Note that the example uses the composite formatting feature, so the ToString method is called implicitly.
Module Example Public Sub Main() Dim raining As Boolean = False Dim busLate As Boolean = True Console.WriteLine("It is raining: {0}", raining) Console.WriteLine("The bus is late: {0}", busLate) End Sub End Module ' The example displays the following output: ' It is raining: False ' The bus is late: True
Because the Boolean structure can have only two values, it is easy to add custom formatting. For simple custom formatting in which other string literals are substituted for "True" and "False", you can use any conditional evaluation feature supported by your language, such as the conditional operator in C# or the If operator in Visual Basic. The following example uses this technique to format Boolean values as "Yes" and "No" rather than "True" and "False".
Module Example Public Sub Main() Dim raining As Boolean = False Dim busLate As Boolean = True Console.WriteLine("It is raining: {0}", If(raining, "Yes", "No")) Console.WriteLine("The bus is late: {0}", If(busLate, "Yes", "No")) End Sub End Module ' The example displays the following output: ' It is raining: No ' The bus is late: Yes
For more complex custom formatting operations, including culture-sensitive formatting, you can call the String.Format(IFormatProvider, String, Object()) method and provide an ICustomFormatter implementation. The following example implements the ICustomFormatter and IFormatProvider interfaces to provide culture-sensitive Boolean strings for the English (United States), French (France), and Russian (Russia) cultures.
Imports System.Globalization Module Example Public Sub Main() Dim cultureNames() As String = { "", "en-US", "fr-FR", "ru-RU" } For Each cultureName In cultureNames Dim value As Boolean = True Dim culture As CultureInfo = CultureInfo.CreateSpecificCulture(cultureName) Dim formatter As New BooleanFormatter(culture) Dim result As String = String.Format(formatter, "Value for '{0}': {1}", culture.Name, value) Console.WriteLine(result) Next End Sub End Module Public Class BooleanFormatter Implements ICustomFormatter, IFormatProvider Private culture As CultureInfo Public Sub New() Me.New(CultureInfo.CurrentCulture) End Sub Public Sub New(culture As CultureInfo) Me.culture = culture End Sub Public Function GetFormat(formatType As Type) As Object _ Implements IFormatProvider.GetFormat If formatType Is GetType(ICustomFormatter) Then Return Me Else Return Nothing End If End Function Public Function Format(fmt As String, arg As Object, formatProvider As IFormatProvider) As String _ Implements ICustomFormatter.Format ' Exit if another format provider is used. If Not formatProvider.Equals(Me) Then Return Nothing ' Exit if the type to be formatted is not a Boolean If Not TypeOf arg Is Boolean Then Return Nothing Dim value As Boolean = CBool(arg) Select culture.Name Case "en-US" Return value.ToString() Case "fr-FR" If value Then Return "vrai" Else Return "faux" End If Case "ru-RU" If value Then Return "верно" Else Return "неверно" End If Case Else Return value.ToString() End Select End Function End Class ' The example displays the following output: ' Value for '': True ' Value for 'en-US': True ' Value for 'fr-FR': vrai ' Value for 'ru-RU': верно
Optionally, you can use resource files to define culture-specific Boolean strings.
The Boolean structure implements the IConvertible interface. As a result, you can use the Convert class to perform conversions between a Boolean value and any other primitive type in the .NET Framework, or you can call the Boolean structure's explicit implementations. However, conversions between a Boolean and the following types are not supported, so the corresponding conversion methods throw an InvalidCastException exception:
Conversion between Boolean and Char (the Convert.ToBoolean(Char) and Convert.ToChar(Boolean) methods)
Conversion between Boolean and DateTime (the Convert.ToBoolean(DateTime) and Convert.ToDateTime(Boolean) methods)
All conversions from integral or floating-point numbers to Boolean values convert non-zero values to true and zero values to false. The following example illustrates this by calling selected overloads of the Convert.ToBoolean class.
Module Example Public Sub Main() Dim byteValue As Byte = 12 Console.WriteLine(Convert.ToBoolean(byteValue)) Dim byteValue2 As Byte = 0 Console.WriteLine(Convert.ToBoolean(byteValue2)) Dim intValue As Integer = -16345 Console.WriteLine(Convert.ToBoolean(intValue)) Dim longValue As Long = 945 Console.WriteLine(Convert.ToBoolean(longValue)) Dim sbyteValue As SByte = -12 Console.WriteLine(Convert.ToBoolean(sbyteValue)) Dim dblValue As Double = 0 Console.WriteLine(Convert.ToBoolean(dblValue)) Dim sngValue As Single = .0001 Console.WriteLine(Convert.ToBoolean(sngValue)) End Sub End Module ' The example displays the following output: ' True ' False ' True ' True ' True ' False ' True
When converting from floating-point values to Boolean values, the conversion methods perform an exact comparison with zero. If the floating-point value has lost precision, the result can be unexpected. This is illustrated in the following example, in which a Double variable whose value should be zero is converted to a Boolean value. As the example shows, the result is true because repeated additions of 0.2 have resulted in a loss of precision.
When converting from Boolean to numeric values, the conversion methods of the Convert class convert true to 1 and false to 0. However, Visual Basic conversion functions convert true to either 255 (for conversions to Byte values) or -1 (for all other numeric conversions). The following example converts true to numeric values by using a Convert method, and, in the case of the Visual Basic example, by using the Visual Basic language's own conversion operator.
Module Example Public Sub Main() Dim flag As Boolean = true Dim byteValue As Byte byteValue = Convert.ToByte(flag) Console.WriteLine("{0} -> {1} ({2})", flag, byteValue, byteValue.GetType().Name) byteValue = CByte(flag) Console.WriteLine("{0} -> {1} ({2})", flag, byteValue, byteValue.GetType().Name) Dim sbyteValue As SByte sbyteValue = Convert.ToSByte(flag) Console.WriteLine("{0} -> {1} ({2})", flag, sbyteValue, sbyteValue.GetType().Name) sbyteValue = CSByte(flag) Console.WriteLine("{0} -> {1} ({2})", flag, sbyteValue, sbyteValue.GetType().Name) Dim dblValue As Double dblValue = Convert.ToDouble(flag) Console.WriteLine("{0} -> {1} ({2})", flag, dblValue, dblValue.GetType().Name) dblValue = CDbl(flag) Console.WriteLine("{0} -> {1} ({2})", flag, dblValue, dblValue.GetType().Name) Dim intValue As Integer intValue = Convert.ToInt32(flag) Console.WriteLine("{0} -> {1} ({2})", flag, intValue, intValue.GetType().Name) intValue = CInt(flag) Console.WriteLine("{0} -> {1} ({2})", flag, intValue, intValue.GetType().Name) End Sub End Module ' The example displays the following output: ' True -> 1 (Byte) ' True -> 255 (Byte) ' True -> 1 (SByte) ' True -> -1 (SByte) ' True -> 1 (Double) ' True -> -1 (Double) ' True -> 1 (Int32) ' True -> -1 (Int32)
For conversions from Boolean to string values, see the Formatting Boolean Values section. For conversions from strings to Boolean values, see the Parsing Boolean Values section.
The Boolean structure includes two static parsing methods, Parse and TryParse, that convert a string to a Boolean value. The string representation of a Boolean value is defined by the case-insensitive equivalents of the values of the TrueString and FalseString fields, which are "True" and "False", respectively. In other words, the only strings that parse successfully are "True", "False", "true", "false", or some mixed-case equivalent. You cannot successfully parse numeric strings such as "0" or "1". Leading or trailing white-space characters are not considered when performing the string comparison.
The following example uses the Parse and TryParse methods to parse a number of strings. Note that only the case-insensitive equivalents of "True" and "False" can be successfully parsed.
Module Example Public Sub Main() Dim values() As String = { Nothing, String.Empty, "True", "False", "true", "false", " true ", "TrUe", "fAlSe", "fa lse", "0", "1", "-1", "string" } ' Parse strings using the Boolean.Parse method. For Each value In values Try Dim flag As Boolean = Boolean.Parse(value) Console.WriteLine("'{0}' --> {1}", value, flag) Catch e As ArgumentException Console.WriteLine("Cannot parse a null string.") Catch e As FormatException Console.WriteLine("Cannot parse '{0}'.", value) End Try Next Console.WriteLine() ' Parse strings using the Boolean.TryParse method. For Each value In values Dim flag As Boolean = False If Boolean.TryParse(value, flag) Console.WriteLine("'{0}' --> {1}", value, flag) Else Console.WriteLine("Cannot parse '{0}'.", value) End If Next End Sub End Module ' The example displays the following output: ' Cannot parse a null string. ' Cannot parse ''. ' 'True' --> True ' 'False' --> False ' 'true' --> True ' 'false' --> False ' ' true ' --> True ' 'TrUe' --> True ' 'fAlSe' --> False ' Cannot parse 'fa lse'. ' Cannot parse '0'. ' Cannot parse '1'. ' Cannot parse '-1'. ' Cannot parse 'string'. ' ' Unable to parse '' ' Unable to parse '' ' 'True' --> True ' 'False' --> False ' 'true' --> True ' 'false' --> False ' ' true ' --> True ' 'TrUe' --> True ' 'fAlSe' --> False ' Cannot parse 'fa lse'. ' Unable to parse '0' ' Unable to parse '1' ' Unable to parse '-1' ' Unable to parse 'string'
If you are programming in Visual Basic, you can use the CBool function to convert the string representation of a number to a Boolean value. "0" is converted to false, and the string representation of any non-zero value is converted to true. If you are not programming in Visual Basic, you must convert your numeric string to a number before converting it to a Boolean. The following example illustrates this by converting an array of integers to Boolean values.
Module Example Public Sub Main() Dim values() As String = { "09", "12.6", "0", "-13 " } For Each value In values Dim success, result As Boolean Dim number As Integer success = Int32.TryParse(value, number) If success Then ' The method throws no exceptions. result = Convert.ToBoolean(number) Console.WriteLine("Converted '{0}' to {1}", value, result) Else Console.WriteLine("Unable to convert '{0}'", value) End If Next End Sub End Module ' The example displays the following output: ' Converted '09' to True ' Unable to convert '12.6' ' Converted '0' to False ' Converted '-13 ' to True
Because Boolean values are either true or false, there is little reason to explicitly call the CompareTo method, which indicates whether an instance is greater than, less than, or equal to a specified value. Typically, to compare two Boolean variables, you call the Equals method or use your language's equality operator.
However, when you want to compare a Boolean variable with the literal Boolean value true or false, it is not necessary to do an explicit comparison, because the result of evaluating a Boolean value is that Boolean value. For example, the expressions
and
Module Example Public Sub Main() Dim hasServiceCharges() As Boolean = { True, False } Dim subtotal As Decimal = 120.62d Dim shippingCharge As Decimal = 2.50d Dim serviceCharge As Decimal = 5.00d For Each hasServiceCharge In hasServiceCharges Dim total As Decimal = subtotal + shippingCharge + If(hasServiceCharge, serviceCharge, 0) Console.WriteLine("hasServiceCharge = {1}: The total is {0:C2}.", total, hasServiceCharge) Next End Sub End Module ' The example displays output like the following: ' hasServiceCharge = True: The total is $128.12. ' hasServiceCharge = False: The total is $123.12.
are equivalent, but the second is more compact. However, both techniques offer comparable performance.
A Boolean value occupies one byte of memory, as the following C# example shows. The example must be compiled with the /unsafe switch.
using System; public struct BoolStruct { public bool flag1; public bool flag2; public bool flag3; public bool flag4; public bool flag5; } public class Example { public static void Main() { unsafe { BoolStruct b = new BoolStruct(); bool* addr = (bool*) &b; Console.WriteLine("Size of BoolStruct: {0}", sizeof(BoolStruct)); Console.WriteLine("Field offsets:"); Console.WriteLine(" flag1: {0}", (bool*) &b.flag1 - addr); Console.WriteLine(" flag1: {0}", (bool*) &b.flag2 - addr); Console.WriteLine(" flag1: {0}", (bool*) &b.flag3 - addr); Console.WriteLine(" flag1: {0}", (bool*) &b.flag4 - addr); Console.WriteLine(" flag1: {0}", (bool*) &b.flag5 - addr); } } } // The example displays the following output: // Size of BoolStruct: 5 // Field offsets: // flag1: 0 // flag1: 1 // flag1: 2 // flag1: 3 // flag1: 4
The byte's low-order bit is used to represent its value. A value of 1 represents true; a value of 0 represents false.
Warning |
|---|
You can use the System.Collections.Specialized.BitVector32 structure to work with sets of Boolean values. |
You can convert a Boolean value to its binary representation by calling the BitConverter.GetBytes(Boolean) method. The method returns a byte array with a single element. To restore a Boolean value from its binary representation, you can call the BitConverter.ToBoolean(Byte(), Int32) method.
The following example calls the BitConverter.GetBytes method to convert a Boolean value to its binary representation and displays the individual bits of the value, and then calls the BitConverter.ToBoolean method to restore the value from its binary representation.
Module Example Public Sub Main() Dim flags() As Boolean = { True, False } For Each flag In flags ' Get binary representation of flag. Dim value As Byte = BitConverter.GetBytes(flag)(0) Console.WriteLine("Original value: {0}", flag) Console.WriteLine("Binary value: {0} ({1})", value, GetBinaryString(value)) ' Restore the flag from its binary representation. Dim newFlag As Boolean = BitConverter.ToBoolean( { value }, 0) Console.WriteLine("Restored value: {0}", flag) Console.WriteLine() Next End Sub Private Function GetBinaryString(value As Byte) As String Dim retVal As String = Convert.ToString(value, 2) Return New String("0"c, 8 - retVal.Length) + retVal End Function End Module ' The example displays the following output: ' Original value: True ' Binary value: 1 (00000001) ' Restored value: True ' ' Original value: False ' Binary value: 0 (00000000) ' Restored value: False
This section illustrates how Boolean values are used in apps. The first section discusses its use as a flag. The second illustrates its use for arithmetic operations.
Boolean variables are most commonly used as flags, to signal the presence or absence of some condition. For example, in the String.Compare(String, String, Boolean) method, the final parameter, ignoreCase, is a flag that indicates whether the comparison of two strings is case-insensitive (ignoreCase is true) or case-sensitive (ignoreCase is false). The value of the flag can then be evaluated in a conditional statement.
The following example uses a simple console app to illustrate the use of Boolean variables as flags. The app accepts command-line parameters that enable output to be redirected to a specified file (the /f switch), and that enable output to be sent both to a specified file and to the console (the /b switch). The app defines a flag named isRedirected to indicate whether output is to be sent to a file, and a flag named isBoth to indicate that output should be sent to the console.
Imports System.IO Imports System.Threading Module Example Public Sub Main() ' Initialize flag variables. Dim isRedirected, isBoth As Boolean Dim fileName As String = "" Dim sw As StreamWriter = Nothing ' Get any command line arguments. Dim args() As String = Environment.GetCommandLineArgs() ' Handle any arguments. If args.Length > 1 Then For ctr = 1 To args.Length - 1 Dim arg As String = args(ctr) If arg.StartsWith("/") OrElse arg.StartsWith("-") Then Select Case arg.Substring(1).ToLower() Case "f" isRedirected = True If args.Length < ctr + 2 Then ShowSyntax("The /f switch must be followed by a filename.") Exit Sub End If fileName = args(ctr + 1) ctr += 1 Case "b" isBoth = True Case Else ShowSyntax(String.Format("The {0} switch is not supported", args(ctr))) Exit Sub End Select End If Next End If ' If isBoth is True, isRedirected must be True. If isBoth And Not isRedirected Then ShowSyntax("The /f switch must be used if /b is used.") Exit Sub End If ' Handle output. If isRedirected Then sw = New StreamWriter(fileName) If Not IsBoth Then Console.SetOut(sw) End If End If Dim msg As String = String.Format("Application began at {0}", Date.Now) Console.WriteLine(msg) If isBoth Then sw.WriteLine(msg) Thread.Sleep(5000) msg = String.Format("Application ended normally at {0}", Date.Now) Console.WriteLine(msg) If isBoth Then sw.WriteLine(msg) If isRedirected Then sw.Close() End Sub Private Sub ShowSyntax(errMsg As String) Console.WriteLine(errMsg) Console.WriteLine() Console.WriteLine("Syntax: Example [[/f <filename> [/b]]") Console.WriteLine() End Sub End Module
A Boolean value is sometimes used to indicate the presence of a condition that triggers a mathematical calculation. For example, a hasShippingCharge variable might serve as a flag to indicate whether to add shipping charges to an invoice amount.
Because an operation with a false value has no effect on the result of an operation, it is not necessary to convert the Boolean to an integral value to use in the mathematical operation. Instead, you can use conditional logic.
The following example computes an amount that consists of a subtotal, a shipping charge, and an optional service charge. The hasServiceCharge variable determines whether the service charge is applied. Instead of converting hasServiceCharge to a numeric value and multiplying it by the amount of the service charge, the example uses conditional logic to add the service charge amount if it is applicable.
Module Example Public Sub Main() Dim hasServiceCharges() As Boolean = { True, False } Dim subtotal As Decimal = 120.62d Dim shippingCharge As Decimal = 2.50d Dim serviceCharge As Decimal = 5.00d For Each hasServiceCharge In hasServiceCharges Dim total As Decimal = subtotal + shippingCharge + If(hasServiceCharge, serviceCharge, 0) Console.WriteLine("hasServiceCharge = {1}: The total is {0:C2}.", total, hasServiceCharge) Next End Sub End Module ' The example displays output like the following: ' hasServiceCharge = True: The total is $128.12. ' hasServiceCharge = False: The total is $123.12.
While marshaling base data types to COM is generally straightforward, the Boolean data type is an exception. You can apply the MarshalAsAttribute attribute to marshal the Boolean type to any of the following representations:
Enumeration type | Unmanaged format |
|---|---|
A 4-byte integer value, where any nonzero value represents true and 0 represents false. This is the default format of a Boolean field in a structure and of a Boolean parameter in platform invoke calls. | |
A 1-byte integer value, where the 1 represents true and 0 represents false. | |
A 2-byte integer value, where -1 represents true and 0 represents false. This is the default format of a Boolean parameter in COM interop calls. |
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
All members of this type are thread safe. Members that appear to modify instance state actually return a new instance initialized with the new value. As with any other type, reading and writing to a shared variable that contains an instance of this type must be protected by a lock to guarantee thread safety.
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