Data Types of Operator Results

發行項
11/18/2006

Visual Basic determines the result data type of an operation based on the data types of the operands. In some cases this might be a data type with a greater range than that of either operand.

Data Type Ranges

The ranges of the relevant data types, in order from smallest to largest, are as follows:

Boolean — two possible values
SByte, Byte — 256 possible integral values
Short, UShort — 65,536 (6.5...E+4) possible integral values
Integer, UInteger — 4,294,967,296 (4.2...E+9) possible integral values
Long, ULong — 18,446,744,073,709,551,615 (1.8...E+19) possible integral values
Decimal — 1.5...E+29 possible integral values, maximum range 7.9...E+28 (absolute value)
Single — maximum range 3.4...E+38 (absolute value)
Double — maximum range 1.7...E+308 (absolute value)

For more information on Visual Basic data types, see Data Type Summary (Visual Basic).

If an operand evaluates to Nothing, the Visual Basic arithmetic operators treat it as zero.

Decimal Arithmetic

Note that the Decimal data type is neither floating-point nor integer.

If either operand of a +, –, *, /, or Mod operation is Decimal and the other is not Single or Double, Visual Basic widens the other operand to Decimal. It performs the operation in Decimal, and the result data type is Decimal.

Floating-Point Arithmetic

Visual Basic performs most floating-point arithmetic in Double, which is the most efficient data type for such operations. However, if one operand is Single and the other is not Double, Visual Basic performs the operation in Single. It widens each operand as necessary to the appropriate data type before the operation, and the result has that data type.

/ and ^ Operators

The / operator is defined only for the Decimal, Single, and Double data types. Visual Basic widens each operand as necessary to the appropriate data type before the operation, and the result has that data type.

The following table shows the result data types for the / operator. Note that this table is symmetric; for a given combination of operand data types, the result data type is the same regardless of the order of the operands.

	Decimal	Single	Double	Any integer type
Decimal	Decimal	Single	Double	Double
Single	Single	Single	Double	Double
Double	Double	Double	Double	Double
Any integer type	Double	Double	Double	Double

The ^ operator is defined only for the Double data type. Visual Basic widens each operand as necessary to Double before the operation, and the result data type is always Double.

Integer Arithmetic

The result data type of an integer operation depends on the data types of the operands. In general, Visual Basic uses the following policies for determining the result data type:

If both operands of a binary operator have the same data type, the result has that data type. An exception is Boolean, which is forced to Short.
If an unsigned operand participates with a signed operand, the result has a signed type with at least as large a range as either operand.
Otherwise, the result usually has the larger of the two operand data types.

Note that the result data type might not be the same as either operand data type.

Note

The result data type is not always large enough to hold all possible values resulting from the operation. An OverflowException exception can occur if the value is too large for the result data type.

Unary + and – Operators

The following table shows the result data types for the two unary operators, + and –.

	Boolean	SByte	Byte	Short	UShort	Integer	UInteger	Long	ULong
Unary +	Short	SByte	Byte	Short	UShort	Integer	UInteger	Long	ULong
Unary –	Short	SByte	Short	Short	Integer	Integer	Long	Long	Decimal

<< and >> Operators

The following table shows the result data types for the two bit-shift operators, << and >>. Visual Basic treats each bit-shift operator as a unary operator on its left operand (the bit pattern to be shifted).

	Boolean	SByte	Byte	Short	UShort	Integer	UInteger	Long	ULong
<<, >>	Short	SByte	Byte	Short	UShort	Integer	UInteger	Long	ULong

If the left operand is Decimal, Single, Double, or String, Visual Basic attempts to convert it to Long before the operation, and the result data type is Long. The right operand (the number of bit positions to shift) must be Integer or a type that widens to Integer.

Binary +, –, *, and Mod Operators

The following table shows the result data types for the binary + and – operators and the * and Mod operators. Note that this table is symmetric; for a given combination of operand data types, the result data type is the same regardless of the order of the operands.

	Boolean	SByte	Byte	Short	UShort	Integer	UInteger	Long	ULong
Boolean	Short	SByte	Short	Short	Integer	Integer	Long	Long	Decimal
SByte	SByte	SByte	Short	Short	Integer	Integer	Long	Long	Decimal
Byte	Short	Short	Byte	Short	UShort	Integer	UInteger	Long	ULong
Short	Short	Short	Short	Short	Integer	Integer	Long	Long	Decimal
UShort	Integer	Integer	UShort	Integer	UShort	Integer	UInteger	Long	ULong
Integer	Integer	Integer	Integer	Integer	Integer	Integer	Long	Long	Decimal
UInteger	Long	Long	UInteger	Long	UInteger	Long	UInteger	Long	ULong
Long	Long	Long	Long	Long	Long	Long	Long	Long	Decimal
ULong	Decimal	Decimal	ULong	Decimal	ULong	Decimal	ULong	Decimal	ULong

\ Operator

The following table shows the result data types for the \ operator. Note that this table is symmetric; for a given combination of operand data types, the result data type is the same regardless of the order of the operands.

	Boolean	SByte	Byte	Short	UShort	Integer	UInteger	Long	ULong
Boolean	Short	SByte	Short	Short	Integer	Integer	Long	Long	Long
SByte	SByte	SByte	Short	Short	Integer	Integer	Long	Long	Long
Byte	Short	Short	Byte	Short	UShort	Integer	UInteger	Long	ULong
Short	Short	Short	Short	Short	Integer	Integer	Long	Long	Long
UShort	Integer	Integer	UShort	Integer	UShort	Integer	UInteger	Long	ULong
Integer	Integer	Integer	Integer	Integer	Integer	Integer	Long	Long	Long
UInteger	Long	Long	UInteger	Long	UInteger	Long	UInteger	Long	ULong
Long	Long	Long	Long	Long	Long	Long	Long	Long	Long
ULong	Long	Long	ULong	Long	ULong	Long	ULong	Long	ULong

If either operand of the \ operator is Decimal, Single, or Double, Visual Basic attempts to convert it to Long before the operation, and the result data type is Long.

Relational and Bitwise Comparisons

The result data type of a relational operation (=, <>, <, >, <=, >=) is always BooleanBoolean Data Type (Visual Basic). The same is true for logical operations (And, AndAlso, Not, Or, OrElse, Xor) on Boolean operands.

The result data type of a bitwise logical operation depends on the data types of the operands. Note that AndAlso and OrElse are defined only for Boolean, and Visual Basic converts each operand as necessary to Boolean before performing the operation.

=, <>, <, >, <=, and >= Operators

If both operands are Boolean, Visual Basic considers True to be less than False. If a numeric type is compared with a String, Visual Basic attempts to convert the String to Double before the operation. A Char or Date operand can be compared only with another operand of the same data type. The result data type is always Boolean.

Bitwise Not Operator

The following table shows the result data types for the bitwise Not operator.

	Boolean	SByte	Byte	Short	UShort	Integer	UInteger	Long	ULong
Not	Boolean	SByte	Byte	Short	UShort	Integer	UInteger	Long	ULong

If the operand is Decimal, Single, Double, or String, Visual Basic attempts to convert it to Long before the operation, and the result data type is Long.

Bitwise And, Or, and Xor Operators

The following table shows the result data types for the bitwise And, Or, and Xor operators. Note that this table is symmetric; for a given combination of operand data types, the result data type is the same regardless of the order of the operands.

	Boolean	SByte	Byte	Short	UShort	Integer	UInteger	Long	ULong
Boolean	Boolean	SByte	Short	Short	Integer	Integer	Long	Long	Long
SByte	SByte	SByte	Short	Short	Integer	Integer	Long	Long	Long
Byte	Short	Short	Byte	Short	UShort	Integer	UInteger	Long	ULong
Short	Short	Short	Short	Short	Integer	Integer	Long	Long	Long
UShort	Integer	Integer	UShort	Integer	UShort	Integer	UInteger	Long	ULong
Integer	Integer	Integer	Integer	Integer	Integer	Integer	Long	Long	Long
UInteger	Long	Long	UInteger	Long	UInteger	Long	UInteger	Long	ULong
Long	Long	Long	Long	Long	Long	Long	Long	Long	Long
ULong	Long	Long	ULong	Long	ULong	Long	ULong	Long	ULong

If an operand is Decimal, Single, Double, or String, Visual Basic attempts to convert it to Long before the operation, and the result data type is the same as if that operand had already been Long.

Miscellaneous Operators

The & operator is defined only for concatenation of String operands. Visual Basic converts each operand as necessary to String before the operation, and the result data type is always String. For the purposes of the & operator, all conversions to String are considered to be widening, even if Option Strict is On.

The Is and IsNot operators require both operands to be of a reference type. The TypeOf...Is expression requires the first operand to be of a reference type and the second operand to be the name of a data type. In all these cases the result data type is Boolean.

The Like operator is defined only for pattern matching of String operands. Visual Basic attempts to convert each operand as necessary to String before the operation. The result data type is always Boolean.

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