[ Private | Public | Friend ] [ Static ] Sub name [ ( arglist ) ]
[ statements ]
[ Exit Sub ]
[ statements ]
The Sub statement syntax has these parts:
|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 statement, 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.|
|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.|
|name||Required. Name of the Sub; follows standard variable naming conventions.|
|arglist||Optional. List of variables representing arguments that are passed to the Sub procedure when it is called. Multiple variables are separated by commas.|
|statements||Optional. Any group of statements to be executed within the Sub procedure.|
The arglist argument has the following syntax and parts:
[ Optional ] [ ByVal | ByRef ] [ ParamArray ] varname [ ( ) ] [ Astype ] [ = defaultvalue ]
|Optional||Optional. Keyword indicating 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 in Visual Basic.|
|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 allows you to provide an arbitrary number of arguments. ParamArray can't be used with ByVal, ByRef, or Optional.|
|varname||Required. 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 (not currently supported), Date, String (variable-length only), Object, Variant, or a specific object type. If the parameter is not Optional, a user-defined type may also be specified.|
|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 doesn't 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. You can't define a Sub procedure inside another Sub, Function, or Property procedure.
The Exit Sub keywords cause 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.
You call a Sub procedure 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 you 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. To avoid this kind of conflict, explicitly declare variables. You can use an Option Explicit statement to force explicit declaration of variables.
You can't use GoSub, GoTo, or Return to enter or exit a Sub procedure.
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, TheWidth) 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