he VBA IsMissing function is used to check whether a variant has been explicitly declared by the programmer or not. It returns a boolean value, either True or False, based on the presence or absence of the declared variant. This function is commonly used in scenarios where optional arguments are passed to a subroutine or function.
VBA IsMissing Function – Purpose, Syntax and Arguments
Syntax:
IsMissing(VariantName)
Arguments:
- VariantName: This is the name of the variant that needs to be checked for explicit declaration.
Example:
Let’s say we have a function named ‘Calculate’ that takes in two optional arguments, ‘num1’ and ‘num2’, and performs some calculation based on them. However, if the user does not provide the values for these arguments, we want to use some default values. This is where the IsMissing function comes into play.
Function Calculate(Optional num1 As Variant, Optional num2 As Variant) As Double
If IsMissing(num1) Then
num1 = 10
End If
If IsMissing(num2) Then
num2 = 20
End If
Calculate = num1 + num2
End Function
In the above code, we are checking whether the arguments ‘num1’ and ‘num2’ have been explicitly declared or not using the IsMissing function. If they have not been explicitly declared, we assign them default values of 10 and 20 respectively. This way, our function can handle both scenarios of arguments being passed or not being passed.
Remarks:
- The IsMissing function can only be used with variant data types as it checks for the absence of an explicitly declared variant.
- If a variant is declared without assigning a value to it, by default, it will be assigned the value of ‘Empty’. In such cases, the IsMissing function will return False.
- If the declared variant is assigned a value using the ‘Assignment’ statement, the IsMissing function will return True.
Important Notes:
- The IsMissing function is a handy tool to handle optional arguments in VBA, making our code more flexible and robust.
- It is always recommended to explicitly declare variables in VBA, as it helps in avoiding unexpected errors and improves code readability.
- The IsMissing function should not be used with non-variant data types such as Integer, String, etc. as it will result in a run-time error.
Understanding VBA IsMissing Function with Examples
Example 1: Using the IsMissing Function to Check if an Optional Argument is Provided
In VBA, arguments can be specified as optional when declaring a procedure. This means that they are not required to be provided when calling the procedure. However, when an optional argument is not provided, it is automatically assigned the value of Empty. The IsMissing function can be used to check if the argument was provided or not.
' Declare a procedure with an optional argument
Sub PrintOptional(Optional value As Variant)
If IsMissing(value) Then
' The argument was not provided
MsgBox "No argument provided!"
Else
' The argument was provided
MsgBox "The provided argument is: " & value
End If
End Sub
' Call the procedure without providing an argument
PrintOptional ' Output: No argument provided!
' Call the procedure with an argument
PrintOptional "Hello" ' Output: The provided argument is: Hello
In this example, the IsMissing function is used to check if the value argument was provided or not. If the argument was not provided, the message “No argument provided!” is displayed. Otherwise, the message “The provided argument is: Hello” is displayed.
Example 2: Using the IsMissing Function with a Variant Array
The IsMissing function can also be used to check if a particular element in a Variant array is declared or not. This is useful when passing arrays as arguments to a procedure.
' Declare a procedure that takes a Variant array as argument
Sub PrintArray(arr As Variant)
If IsMissing(arr(0)) Then
' The first element of the array is not declared
MsgBox "Array is empty!"
Else
' The first element of the array is declared
MsgBox "The first element of the array is: " & arr(0)
End If
End Sub
' Declare an empty Variant array
Dim myArray() As Variant
' Call the procedure with an empty array
PrintArray myArray ' Output: Array is empty!
' Redefine the array with values
myArray = Array(1, 2, 3)
' Call the procedure with the populated array
PrintArray myArray ' Output: The first element of the array is: 1
In this example, the IsMissing function is used to check if the first element of the arr argument is declared or not. If the element is not declared, the message “Array is empty!” is displayed. Otherwise, the first element of the array is displayed.
Example 3: Using the IsMissing Function to Check for Missing Arguments in a User-defined Function
The IsMissing function can also be used in user-defined functions to check for missing arguments. If an argument is missing, the function can either prompt the user for the missing argument or skip the calculation and return Empty.
' Declare a function that calculates the average of a range of values
Function Average(RangeArray As Variant) As Double
Dim sum As Double, count As Integer, i As Integer
For i = LBound(RangeArray) To UBound(RangeArray)
sum = sum + RangeArray(i)
count = count + 1
Next i
Average = sum / count
End Function
' Call the function without providing an argument
Dim avg As Double
avg = Average() ' This will raise a "Compile error: Missing argument" error
' Modify the function to check for missing argument
Function Average(RangeArray As Variant) As Double
If IsMissing(RangeArray) Then
' Ask the user to enter the missing argument
RangeArray = InputBox("Please enter a range of values")
End If
Dim sum As Double, count As Integer, i As Integer
For i = LBound(RangeArray) To UBound(RangeArray)
sum = sum + RangeArray(i)
count = count + 1
Next i
Average = sum / count
End Function
' Call the function without providing an argument
avg = Average() ' The user will be prompted to enter a range of values
In this example, the IsMissing function is used to check if the RangeArray argument is provided or not. If the argument is missing, the user will be prompted to enter a range of values. This prevents the Compile error: Missing argument error that would occur if the function is called without providing an argument.
Example 4: Using the IsMissing Function with Optional ByVal and Default Arguments
The IsMissing function can also be used when dealing with Optional ByVal and Optional ByVal arguments that have default values.
' Declare a procedure with an optional argument
Sub PrintOptional(Optional ByVal value As Variant = "Default value")
If IsMissing(value) Then
' The argument was not provided, use the default value
MsgBox "The value was not provided, using the default value instead!"
Else
' The argument was provided
MsgBox "The provided argument is: " & value
End If
End Sub
' Call the procedure without providing an argument
PrintOptional ' Output: The value was not provided, using the default value instead!
' Call the procedure with an argument
PrintOptional "Hello" ' Output: The provided argument is: Hello
In this example, the IsMissing function is used to check if the value argument was provided or not. If the argument is not provided, the default value “Default value” will be used instead. Otherwise, the provided argument will be displayed.
Conclusion
The IsMissing function is a useful tool in VBA for checking if an argument was provided or not. It can be used in various scenarios, such as checking for missing arguments in procedures or user-defined functions. By using this function, you can ensure that your code runs smoothly and prevents any unexpected errors when dealing with optional arguments.
