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        VB.NET Concatenation Operators
 
        & Operator
  Syntax
  Parts
  Remarks
  See also
 
        + Operator
  Syntax
  Parts
  Result
  Supported Types
  Remarks
  Overloading
  See also
 
        Source/Reference

VB.NET Concatenation Operators

The supporting VB.NET Concatenation Operators are &, +.

& Operator

Generates a string concatenation of two expressions.

Syntax

result = expression1 & expression2

Parts

result: Required. Any String or Object variable.

expression1: Required. Any expression with a data type that widens to String.

expression2: Required. Any expression with a data type that widens to String.

Remarks

If the data type of expression1 or expression2 is not String but widens to String, it is converted to String. If either of the data types does not widen to String, the compiler generates an error.

The data type of result is String. If one or both expressions evaluate to Nothing or have a value of DBNull.Value, they are treated as a string with a value of "".

Note

The & operator can be overloaded, which means that a class or structure can redefine its behavior when an operand has the type of that class or structure. If your code uses this operator on such a class or structure, be sure you understand its redefined behavior. For more information, see Operator Procedures.

Note

The ampersand (&) character can also be used to identify variables as type Long. For more information, see Type Characters.

+ Operator

Addition operator. Adds two numbers or returns the positive value of a numeric expression. Can also be used to concatenate two string expressions.

Syntax

expression1 + expression2  
- or -  
+ expression1

Parts

expression1: Required. Any numeric or string expression.

expression2: Required unless the + operator is calculating a negative value. Any numeric or string expression.

Result

If expression1 and expression2 are both numeric, the result is their arithmetic sum.

If expression2 is absent, the + operator is the unary identity operator for the unchanged value of an expression. In this sense, the operation consists of retaining the sign of expression1, so the result is negative if expression1 is negative.

If expression1 and expression2 are both strings, the result is the concatenation of their values.

If expression1 and expression2 are of mixed types, the action taken depends on their types, their contents, and the setting of the Option Strict Statement. For more information, see the tables in "Remarks."

Supported Types

All numeric types, including the unsigned and floating-point types and Decimal, and String.

Remarks

In general, + performs arithmetic addition when possible, and concatenates only when both expressions are strings.

If neither expression is an Object, Visual Basic takes the following actions.

Data types of expressions	Action by compiler
Both expressions are numeric data types (SByte, Byte, Short, UShort, Integer, UInteger, Long, ULong, Decimal, Single, or Double)	Add. The result data type is a numeric type appropriate for the data types of expression1 and expression2. See the "Integer Arithmetic" tables in Data Types of Operator Results.
Both expressions are of type String	Concatenate.
One expression is a numeric data type and the other is a string	If Option Strict is On, then generate a compiler error. If Option Strict is Off, then implicitly convert the String to Double and add. If the String cannot be converted to Double, then throw an InvalidCastException exception.
One expression is a numeric data type, and the other is Nothing	Add, with Nothing valued as zero.
One expression is a string, and the other is Nothing	Concatenate, with Nothing valued as "".

If one expression is an Object expression, Visual Basic takes the following actions.

Data types of expressions	Action by compiler
Object expression holds a numeric value and the other is a numeric data type	If Option Strict is On, then generate a compiler error. If Option Strict is Off, then add.
Object expression holds a numeric value and the other is of type String	If Option Strict is On, then generate a compiler error. If Option Strict is Off, then implicitly convert the String to Double and add. If the String cannot be converted to Double, then throw an InvalidCastException exception.
Object expression holds a string and the other is a numeric data type	If Option Strict is On, then generate a compiler error. If Option Strict is Off, then implicitly convert the string Object to Double and add. If the string Object cannot be converted to Double, then throw an InvalidCastException exception.
Object expression holds a string and the other is of type String	If Option Strict is On, then generate a compiler error. If Option Strict is Off, then implicitly convert Object to String and concatenate.

If both expressions are Object expressions, Visual Basic takes the following actions (Option Strict Off only).

Data types of expressions	Action by compiler
Both Object expressions hold numeric values	Add.
Both Object expressions are of type String	Concatenate.
One Object expression holds a numeric value and the other holds a string	Implicitly convert the string Object to Double and add. If the string Object cannot be converted to a numeric value, then throw an InvalidCastException exception.

If either Object expression evaluates to Nothing or DBNull, the + operator treats it as a String with a value of "".

Note

When you use the + operator, you might not be able to determine whether addition or string concatenation will occur. Use the & operator for concatenation to eliminate ambiguity and to provide self-documenting code.

Overloading

The + operator can be overloaded, which means that a class or structure can redefine its behavior when an operand has the type of that class or structure. If your code uses this operator on such a class or structure, be sure you understand its redefined behavior. For more information, see Operator Procedures.

Source/Reference

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ID: 200800002 Last Updated: 8/2/2020 Revision: 0 Ref:

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