Function Statement

Description

Declares the name, arguments, and code that form the body of a Function procedure.

Syntax

[Public | Private][Static] Function name [(arglist)][As type]
[statements]
[name = expression]
[Exit Function]
[statements]
[name = expression]
End Function

The Function statement syntax has these parts:

The arglist argument has the following syntax and parts:

[Optional][ByVal | ByRef][ParamArray] varname[( )][As type]

Remarks

If not explicitly specified using either Public or Private, Function procedures are Public by default. If Static is not used, the value of local variables is not preserved between calls.

All executable code must be in procedures. You can't define a Function procedure inside another Function, Sub, or Property procedure.

The Exit Function keywords cause an immediate exit from a Function procedure. Program execution continues with the statement following the statement that called the Function procedure. Any number of Exit Function statements can appear anywhere in a Function procedure.

Like a Sub procedure, a Function procedure is a separate procedure that can take arguments, perform a series of statements, and change the values of its arguments. However, unlike a Sub procedure, a Function procedure can be used on the right hand side of an expression in the same way you use any intrinsic function, such as Sqr, Cos, or Chr, when you want to use the value returned by the function.

You call a Function procedure using the function name, followed by the argument list in parentheses, in an expression. If the function has no arguments, you still must include the parentheses. See the Call statement for specific information on how to call Function procedures.

Caution

Function procedures can be recursive; that is, they can call themselves to perform a given task. However, recursion can lead to stack overflow. The Static keyword is usually not used with recursive Function procedures.

To return a value from a function, assign the value to the function name. Any number of such assignments can appear anywhere within the procedure. If no value is assigned to name, the procedure returns a default value: a numeric function returns 0, a string function returns a zero-length string (""), and a Variant function returns Empty. A function that returns an object reference returns Nothing if no object reference is assigned to name (using Set) within the Function.

The following example shows how to assign a return value to a function named BinarySearch. In this case, False is assigned to the name to indicate that some value was not found.

Function BinarySearch(. . .) As Boolean
. . .
    ' Value not found. Return a value of False.
    If lower > upper Then
        BinarySearch = False
        Exit Function
    End If
. . .
End Function

Variables used in Function procedures fall into two categories: those that are explicitly declared within the procedure and those that are not. Variables that are explicitly declared in a procedure (using Dim or the equivalent) are always local to the procedure. Other variables used but not explicitly declared in a procedure are also local unless they are explicitly declared at some higher level outside the procedure.

Caution

A procedure can use a variable that is not explicitly declared in the procedure, but a name conflict can occur if anything you have defined at the module level has the same name. If your procedure refers to an undeclared variable that has the same name as another procedure, constant or variable, it is assumed that your procedure is referring to that module-level name. Explicitly declare variables to avoid this kind of conflict. You can use an Option Explicit statement to force explicit declaration of variables.

Caution

Arithmetic expressions may be rearranged to increase internal efficiency. Avoid using a Function procedure in an arithmetic expression when the function changes the value of variables in the same expression.

See Also

Call Statement, Dim Statement, Option Explicit Statement, Property Get Statement, Property Let Statement, Property Set Statement, Set Statement, Static Statement, Sub Statement.

Example

This example uses the Function statement to declare the name, arguments and code that form the body of a Function procedure.

' The following user-defined function returns the square root of the
' argument passed to it.
Function CalculateSquareRoot(NumberArg As Double) As Double
    If NumberArg < 0 Then    ' Evaluate argument.
        Exit Function    ' Exit to calling procedure.
    Else
        CalculateSquareRoot = Sqr(NumberArg)    ' Return square root.
    EndIf
End Function

' Using the ParamArray keyword enables a function to accept a variable
' number of arguments. In the following definition, FirstArg is passed
' by value.
Function CalcSum(ByVal FirstArg As Integer, ParamArray OtherArgs())
' If the function is invoked as...
ReturnValue = CalcSum(4,3,2,1)
' Local variables get the following values: FirstArg=4, OtherArgs(1)=3,
' OtherArgs(2) = 2 and so on, assuming default lower bound for 
' arrays = 1.

' If a function's arguments are defined as...
Function MyFunc(MyStr As String, Optional MyArg1, Optional MyArg2) 
' It can be invoked in the following ways.
RetVal = MyFunc("Hello", 2, "World")    ' All 3 arguments supplied.
RetVal = MyFunc("Test", , 5)    ' Second argument omitted.
RetVal = MyFunc("Test")    ' First argument only.