What are the benefits and risks of using the StrPtr function in VBA?

Question

While looking for a way to test when a user cancels an InputBox, I stumbled across the StrPtr function. I believe it checks if a variable was ever

Answer 1

I tired both using StrPtr and without using StrPtr. I tested my Sub with several examples. I got same results except in one occasion - When User inputs null value (nothing) and presses OK. Precisely I tried these two:

Using StrPtr. "Invalid Number" was the result here

    ElseIf StrPtr(Max_hours_string) = 0 
            MsgBox "Cancelled"
    Else
            MsgBox "Invalid Number"

Without Using StrPtr. "Cancelled" was the result here

 ElseIf Max_hours_string = "" Then
        MsgBox "Cancelled"
 Else
        MsgBox "Invalid Number"

This is my code.

Sub Input_Max_Hours_From_The_User()
        'Two Common Error Cases are Covered:
        '1. When using InputBox, you of course have no control over whether the user enters valid input.
        '        You should store user input into a string, and then make sure you have the right value.
        '2. If the user clicks Cancel in the inputbox, the empty string is returned.
                 'Since the empty string can't be implicitly coerced to a double, an error is generated.
                 'It is the same thing that would happen if the user entered "Haughey" in the InputBox.

     Dim Max_hours_string As String, Max_hours_double As Double
        Max_hours_string = InputBox("Enter Maximum hours of any Shift")
        If IsNumeric(Max_hours_string) Then
            Max_hours_double = CDbl(Max_hours_string) 'CDbl converts an expression to double
            Range("L6").Value = Max_hours_double
            Range("L6").Interior.ColorIndex = 37
        ElseIf StrPtr(Max_hours_string) = 0 Then 'ElseIf Max_hours_string = "" Then MsgBox "Cancelled"  also works !
            MsgBox "Cancelled"
        Else
            MsgBox "Invalid Number"
        End If

    End Sub

So I think it depends how important it is to handle the null value for you. All other test cases, including pressing Cancel, non-numerical inputs etc. give the same results. Hope this helps.