A bool instance can have either of two values: true, or false.

The bool structure provides methods that support the following tasks:

• Converting Boolean values to strings: bool.ToString

• Parsing strings to convert them to Boolean values: bool.Parse(string) and bool.TryParse(string, Boolean@)

• Comparing values: bool.CompareTo(bool) and bool.Equals(bool)

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

Formatting Boolean values

The string representation of a bool is either "True" for a true value or "False" for a false value. The string representation of a bool value is defined by the read-only bool.TrueString and bool.FalseString fields.

You use the bool.ToString method to convert Boolean values to strings. The Boolean structure includes two bool.ToString overloads: the parameterless bool.ToString method and the bool.ToString(IFormatProvider) method, which includes a parameter that controls formatting. However, because this parameter is ignored, the two overloads produce identical strings. The bool.ToString(IFormatProvider) method does not support culture-sensitive formatting.

The following example illustrates formatting with the bool.ToString method. Note that the example uses the composite formatting feature, so the bool.ToString method is called implicitly.

code reference: System.Boolean.Structure#3

Because the bool 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 bool values as "Yes" and "No" rather than "True" and "False".

code reference: System.Boolean.Structure#4

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.

code reference: System.Boolean.Structure#5

Optionally, you can use resource files to define culture-specific Boolean strings.

Converting to and from Boolean values

The bool structure implements the IConvertible interface. As a result, you can use the Convert class to perform conversions between a bool value and any other primitive type in the .NET Framework, or you can call the bool structure's explicit implementations. However, conversions between a bool and the following types are not supported, so the corresponding conversion methods throw an InvalidCastException exception:

• Conversion between bool and char (the Convert.ToBoolean(char) and Convert.ToChar(bool) methods)

• Conversion between bool and DateTime (the Convert.ToBoolean(DateTime) and Convert.ToDateTime(bool) 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(long) class.

code reference: System.Boolean.Structure#6

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.

code reference: System.Boolean.Structure#8

For conversions from bool to string values, see the Formatting Boolean Values section. For conversions from strings to bool values, see the Parsing Boolean Values section.

Parsing Boolean values

The bool structure includes two static parsing methods, bool.Parse(string) and bool.TryParse(string, Boolean@), 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 bool.TrueString and bool.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 bool.Parse(string) and bool.TryParse(string, Boolean@) methods to parse a number of strings. Note that only the case-insensitive equivalents of "True" and "False" can be successfully parsed.

code reference: System.Boolean.Structure#2

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.

code reference: System.Boolean.Structure#9

Comparing Boolean values

Because Boolean values are either true or false, there is little reason to explicitly call the bool.CompareTo(bool) 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 bool.Equals(bool) 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

code reference: System.Boolean.Structure#12

and

code reference: System.Boolean.Structure#13

are equivalent, but the second is more compact. However, both techniques offer comparable performance.

Working with Booleans as binary values

A Boolean value occupies one byte of memory. The byte's low-order bit is used to represent its value. A value of 1 represents true; a value of 0 represents false.

You can convert a Boolean value to its binary representation by calling the BitConverter.GetBytes(bool) 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[], int) method.

The following example calls the BitConverter.GetBytes(bool) method to convert a Boolean value to its binary representation and displays the individual bits of the value, and then calls the BitConverter.ToBoolean(Byte[], int) method to restore the value from its binary representation.

code reference: System.Boolean.Structure#1

Performing operations with Boolean values

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 values as flags

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, bool) 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.

code reference: System.Boolean.Structure#10

Booleans and arithmetic operations

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.

code reference: System.Boolean.Structure#13

This type is safe for multithreaded operations.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)
Assembly Versions: 1.0.5000.0, 2.0.0.0, 4.0.0.0