Functions in VB6 are often used to perform data manipulation on numbers or strings and return the result. Suppose there is the possibility of an error in the function—not a run-time error but a program-definer error such as invalid data. If you want to return a value from the function that signals an error to the calling code, you simply use the CVErr and IsError functions.
The CVErr function converts a type Variant into the subtype Error. You can detect this with the IsError function. Here's the strategy:
- Declare your function with a Variant return type, which will work for both string and number data.
- If the function executes properly, assign the return value as usual:
MyFunction = value
- If there's a problem and you need to return an error value, use CVErr to return an error with some numerical value:
MyFunction = CVErr(SomeNumericalValue)
- In the calling program, use IsError like this:
ReturnValue = MyFunction()
If IsError(ReturnValue) Then
' Deal with error here.
Else
' Deal with non-error return value here.
End If
The ability to signal an error with a function's return value is very useful in some situations.
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