You can use the Eval function to evaluate an expression (expression: A combination of operators, field names, functions, literals, and constants that evaluates to a single value. Expressions can specify criteria (such as Order Amount>10000) or perform calculations on field values (such as Price*Quantity).) that results in a text string or a numeric value.

You can construct a string and then pass it to the Eval function as if the string were an actual expression. The Eval function evaluates the string expression (string expression: An expression that evaluates to a sequence of contiguous characters. Elements of the expression can be: functions that return a string or a string Variant (VarType 8); a string literal, constant, variable, or Variant.) and returns its value. For example, Eval("1 + 1") returns 2.

If you pass to the Eval function a string that contains the name of a function, the Eval function returns the return value of the function. For example, Eval("Chr$(65)") returns "A".

Syntax

Eval(stringexpr)

The stringexpr argument is an expression that evaluates to an alphanumeric text string. For example, stringexpr can be a function that returns a string or a numeric value. Or it can be a reference to a control (control: A graphical user interface object, such as a text box, check box, scroll bar, or command button, that lets users control the program. You use controls to display data or choices, perform an action, or make the user interface easier to read.) on a form. The stringexpr argument must evaluate to a string or numeric value; it can't evaluate to a Microsoft Access object (Microsoft Access object: An object defined by Access that relates to Access, its interface, or an application's forms, reports, and data access pages, and that you use to program the elements of the interface used for entering and displaying data.).

 Note   Examples that follow demonstrate the use of this function in a Visual Basic for Applications (VBA) module. For more information about working with VBA, select Developer Reference in the drop-down list next to Search and enter one or more terms in the search box.

 Note   If you are passing the name of a function to the Eval function, you must include parentheses after the name of the function in the stringexpr argument. For example:

' ShowNames is user-defined function.
Debug.Print Eval("ShowNames()")   
		

Debug.Print Eval("StrComp(""Joe"",""joe"", 1)")
		

Debug.Print Eval("Date()")
		

Remarks

You can use the Eval function in a calculated control (calculated control: A control that is used on a form, report, or data access page to display the result of an expression. The result is recalculated each time there is a change in any of the values on which the expression is based.) on a form or report, or in a macro or module. The Eval function returns a Variant (Variant data type: The default data type for variables that don't have type-declaration characters when a Deftype statement isn't in effect. A Variant can store numeric, string, date/time, Null, or Empty data.) that is either a string or a numeric type.

The argument stringexpr must be an expression that is stored in a string. If you pass to the Eval function a string that doesn't contain a numeric expression or a function name but only a simple text string, a run-time error (run-time error: An error that can be detected only when an application is running.) occurs. For example, Eval("Smith") results in an error.

You can use the Eval function to determine the value stored in the Value property of a control. The following example passes a string containing a full reference to a control to the Eval function. It then displays the current value of the control in a dialog box.

Dim ctl As Control
Dim strCtl As String

Set ctl = Forms!Employees!LastName
strCtl = "Forms!Employees!LastName"
MsgBox ("The current value of " & ctl.Name & _
    " is " & Eval(strCtl))
		

You can use the Eval function to access expression operators that aren't ordinarily available in a Visual Basic for Applications (VBA) module. For example, you can't use the SQL operators Between...And or In directly in your code, but you can use them in an expression passed to the Eval function.

The next example determines whether the value of a ShipRegion control on an Orders form is one of several specified state abbreviations. If the field contains one of the abbreviations, intState will be True (–1). Note that you use single quotation marks (') to include a string within another string.

Dim intState As Integer
intState = Eval("Forms!Orders!ShipRegion In " _
    & "('AK', 'CA', 'ID', 'WA', 'MT', 'NM', 'OR')")
		

Example

The following example assumes that you have a series of 50 functions defined as A1, A2, and so on. This example uses the Eval function to call each function in the series.

Sub CallSeries()

    Dim intI As Integer

    For intI = 1 To 50
        Eval("A" & intI & "()")
    Next intI

End Sub
		

The next example triggers a Click event as if the user had clicked a button on a form. If the value of the button's OnClick property begins with an equal sign (=), signifying that it is the name of a function, the Eval function calls the function, which is equivalent to triggering the Click event. If the value doesn't begin with an equal sign, then the value must name a macro. The RunMacro method of the DoCmd object runs the named macro.

Dim ctl As Control
Dim varTemp As Variant

Set ctl = Forms!Contacts!HelpButton
If (Left(ctl.OnClick, 1) = "=") Then
    varTemp = Eval(Mid(ctl.OnClick,2))
Else
    DoCmd.RunMacro ctl.OnClick
End If