ACC: "Invalid Use of Null" with SysCmd() Function

• Microsoft Access versions 1.1, 2.0

SYMPTOMS

Moderate: Requires basic macro, coding, and interoperability skills.

When you use the SysCmd() function in Access Basic code, you may receive the error message "Invalid use of Null."

CAUSE

This error message occurs when the SysCmd() function returns a null value and the return variable is declared as any data type other than Variant.

RESOLUTION

Make sure that the return variable for each call to the SysCmd() function has a Variant data type.

STATUS

This behavior no longer occurs in Microsoft Access version 7.0.

MORE INFORMATION

The only Access Basic data type that can hold a null value is the Variant data type. Since the SysCmd() function frequently returns a null value, the return variable should have the Variant data type, as in the following example:

   Dim ReturnVal As Variant
   ReturnVal = SysCmd(4, "Status Bar Text Message")

If you do not explicitly declare the return variable's data type, it is implicitly declared as a Variant data type, so the following example works as well:

   Dim ReturnVal
   ReturnVal = SysCmd(4, "Status Bar Text Message")

Steps to Reproduce Behavior

1. Start Microsoft Access and open any database.

2. Create a new module and enter the following line in the module's Declarations section:

         Option Explicit
   

3. Enter the following code in the module:

         Sub SysCmdDemo1 ()
            Dim ReturnVal As Integer
            ReturnVal = SysCmd(4, "SysCmd Fails")
         End Sub
   
   

4. From the View menu, choose Immediate Window.

5. Type the following line in the Immediate window and then press ENTER:

         SysCmdDemo1
   

   You receive the error message stated above.

REFERENCES