Usually the code in a procedure needs some information about the state of the program to do its job. This information consists of variables passed to the procedure when it is called. When a variable is passed to a procedure, it is called an argument. The arguments for procedures you write have the Variant data type by default.
However, you can declare other data types for arguments. For example, the following function accepts a string and an integer:. You can also see the Language Reference for specific data types. Only a copy of a variable is passed when an argument is passed by value. If the procedure changes the value, the change affects only the copy and not the variable itself.
Use the ByVal keyword to indicate an argument passed by value. Passing arguments by reference gives the procedure access to the actual variable contents in its memory address location. As a result, the variable's value can be permanently changed by the procedure to which it is passed. Passing by reference is the default in Visual Basic. If you specify a data type for an argument passed by reference, you must pass a value of that type for the argument.
You can work around this by passing an expression, rather than a data type, for an argument. Visual Basic evaluates an expression and passes it as the required type if it can.
The simplest way to turn a variable into an expression is to enclose it in parentheses. For example, to pass a variable declared as an integer to a procedure expecting a string as an argument, you would do the following:. You can specify arguments to a procedure as optional by placing the Optional keyword in the argument list.
8 ways to return multiple values from a VBA function (Part 1: Using By Reference argument, collection, and dictionary object)
If you specify an optional argument, all subsequent arguments in the argument list must also be optional and declared with the Optional keyword. The two pieces of sample code below assume there is a form with a command button and list box.
Writing Your Own Functions In VBA
In the case where an optional argument is not provided, the argument is actually assigned as a variant with the value of Empty. The example above shows how to test for missing optional arguments using the IsMissing function. It's also possible to specify a default value for an optional argument.
The following example returns a default value if the optional argument isn't passed to the function procedure:.
Generally, the number of arguments in the procedure call must be the same as in the procedure specification.
Using the ParamArray keyword allows you to specify that a procedure will accept an arbitrary number of arguments. This allows you to write functions like Sum:. For many built-in functions, statements, and methods, Visual Basic provides the option of using named arguments as a shortcut for typing argument values.
With named arguments, you can provide any or all of the arguments, in any order, by assigning a value to the named argument. You do this by typing the argument name plus a colon followed by an equal sign and the value MyArgument: Notice that the arguments in the following example are in the reverse order of the expected arguments:.
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This is especially useful if your procedures have several optional arguments that you do not always need to specify. To determine which functions, statements, and methods support named arguments, use the AutoQuickInfo feature in the Code window, check the Object Browser, or see the Language Reference.
Consider the following when working with named arguments:. You can omit only the optional arguments. For Visual Basic VB and Visual Basic for applications VBA object libraries, the Object Browser encloses optional arguments with square brackets [ ]. Downloads Visual Studio SDKs Trial software Free downloads Office resources SharePoint Server resources SQL Server Express resources Windows Server resources Programs Subscriptions Overview Administrators Students Microsoft Imagine Microsoft Student Partners ISV Startups Events Community Magazine Forums Blogs Channel 9 Documentation APIs and reference Dev centers Samples Retired content.
The content you requested has been removed. Visual Basic Basics Programming Fundamentals Introduction to Procedures. Introduction to Procedures Passing Arguments to Procedures. Passing Arguments to Procedures. Collapse the table of content.
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