Sub

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

Syntax:

[ attributes ]
[ Public | Private | Friend | Protected ] [ Static ] [ Overridable ] Sub name [ ( Of typevars ) ] [ ( arglist ) ] [ binding-clause ]
     [ statements ] …
     [ Exit Sub ] …
     [ statements ] …
End Sub

attributes

optional One or more of the supported attributes for procedures.

Public

optional Indicates that the Sub procedure is accessible to all other procedures in all modules. If used in a module that contains an Option Private, the procedure is not available outside the project.

Private

optional Indicates that the Sub procedure is accessible only to other procedures in the module where it is declared.

Friend

optional Used only in a class module. Indicates that the Sub procedure is visible throughout the project, but not visible to a controller of an instance of an object.

Protected

optional (twinBASIC) Used only in a class. Indicates that the Sub procedure is accessible from inside the declaring class and from classes that derive from it via Inherits, but not from outside callers.

Static

optional Indicates that the Sub procedure’s local variables are preserved between calls. The Static attribute doesn’t affect variables that are declared outside the Sub, even if they are used in the procedure.

Overridable

optional (twinBASIC) Marks the Sub as an inheritance hook that classes derived via Inherits may replace with an Overrides clause. Meaningful only on a member of a class that participates in an Inherits hierarchy.

name

Name of the Sub; follows standard variable naming conventions. The special name New declares an instance constructor — see Inheritance for chained construction with *baseclass*.New(...).

Of typevars

optional One or more type variable names, following standard variable naming conventions. The names are separated by commas. Causes the procedure to be a generic Sub.

arglist

optional List of variables representing arguments that are passed to the Sub procedure when it is called. Multiple variables are separated by commas. See arglist below for syntax.

binding-clause

optional (twinBASIC) One of three trailing clauses that bind this body to a member declared elsewhere:

Handles object.event [ , object.event … ] — connects this Sub as a handler for the named event(s), replacing the traditional Object_Event naming convention. See Handles statement.
Implements iface.member [ , iface2.member2 … ] — provides the body for the named Interface (or Class) member, replacing the traditional Iface_Member naming convention. A comma-separated list permits one body to satisfy several interfaces’ members at once. See Implements statement.
Overrides base.member — supplies the body for an Overridable member inherited via Inherits. Combine with Overridable on the same header to allow further-derived classes to override again.

statements

optional Any group of statements to be executed within the Sub procedure.

Exit Sub

optional Immediately returns from the Sub procedure. (A bare Return statement does not exit a Sub — it is reserved for the GoSub…Return construct.)

arglist

Syntax: One or more of
[ Optional ] [ ByVal | ByRef ] [ ParamArray ] varname [ () ] [ As type ] [ = defaultvalue ]

Optional: optional Indicates that an argument is not required. If used, all subsequent arguments in arglist must also be optional and declared by using the Optional keyword. Optional can’t be used for any argument if ParamArray is used.
ByVal: optional Indicates that the argument is passed by value.
ByRef: optional Indicates that the argument is passed by reference. ByRef is the default unlike in Visual Basic .NET.
ParamArray: optional Used only as the last argument in arglist to indicate that the final argument is an Optional array of Variant elements. The ParamArray keyword permits passing an arbitrary number of arguments. It may not be used with ByVal, ByRef, or Optional.
varname: Name of the variable representing the argument; follows standard variable naming conventions.
type: optional Data type of the argument passed to the procedure; may be Byte, Boolean, Integer, Long, Currency, Single, Double, Decimal, Date, String (variable length only), Object, Variant, a specific object type, or the name of a generic type argument. If the parameter is not Optional, a user-defined type may also be specified.
If the name of a generic type parameter is used, it becomes bound to the concrete type of the argument passed to the procedure. The name binding has the scope of the body of the procedure.
defaultvalue: optional Any constant or constant expression. Valid for Optional parameters only. If the type is an Object, an explicit default value can only be Nothing.

If not explicitly specified by using Public, Private, or Friend, Sub procedures are public by default.

If Static isn’t used, the value of local variables is not preserved between calls.

The Friend keyword can only be used in class modules. However, Friend procedures can be accessed by procedures in any module of a project. A Friend procedure does not appear in the type library of its parent class, nor can a Friend procedure be late bound.

Sub 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 usually is not used with recursive Sub procedures.

All executable code must be in procedures. A Sub procedure cannot be defined inside another Sub, Function, or Property procedure.

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

Like a Function procedure, a Sub procedure is a separate procedure that can take arguments, perform a series of statements, and change the value of its arguments. However, unlike a Function procedure, which returns a value, a Sub procedure can’t be used in an expression.

A Sub procedure is called by using the procedure name followed by the argument list. See the Call statement for specific information about how to call Sub procedures.

Variables used in Sub 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. Variables that are used but not explicitly declared in a procedure are also local unless they are explicitly declared at some higher level outside the procedure.

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

Note

GoSub, GoTo, and Return cannot enter or exit a Sub procedure. Use Exit Sub to leave a Sub early.

Example

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

' Sub procedure definition.
' Sub procedure with two arguments.
Sub SubComputeArea(Length As Double, TheWidth As Double)
    Dim Area As Double ' Declare local variable.

    If Length = 0 Or TheWidth = 0 Then
        ' If either argument = 0.
        Exit Sub ' Exit Sub immediately.
    End If

    Area = Length * TheWidth ' Calculate area of rectangle.
    Debug.Print Area ' Print Area to Debug window.
End Sub

Sub

arglist

Example

See Also