String default parameter value issue after conversion from VB6 to VB.Net

Question

We have a legacy component that has been converted from VB6 to VB.Net.

The VB component was called from an ASPX page using Request("param") to pass optional parameters to function calls. That means the value is null/nothing if the parameter is not present.

The parameters were then added to an ADODB call of a store procedure using Parameters.Append.

When used from VB6 missing, Request("param") values were coerced into empty strings when passed to the VB6 component. This meant that the ADODB call was satisfied (for required parameters).

When the code was ported to VB.Net, the null Request("param") values are now passed as null values (VB nothing?) and Parameters.Append skips adding the value if it is nothing. This caused the stored procedure calls to break as a required param was missing.

My question is:

If we change the component's function parameters to be optional and have paramname as string = "" defaults, will a null/nothing value be converted to an empty string, or is null/nothing treated differently to a parameter being simply missing?

Apologies for the use of the term null, but 99% of my work is C# :)

Joel Coehoorn · Accepted Answer · 2012-03-09 15:29:43Z

8

If you pass Nothing as the argument for an Optional String parameter that defaults to an empty string, the variable inside the method will have a value of Nothing. It will not have the value of an empty string. They are two different values, because strings in .Net are reference types. You should add code to top of the method to replace Nothing for those parameters with an empty string.

answered Mar 9, 2012 at 15:29

Joel Coehoorn

419k114 gold badges582 silver badges820 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

iCollect.it Ltd Over a year ago

+15: That was the assumption, thanks for confirming it. I gather that means the default values are nothing more than a complier clue and all parameters are actually passed. We will add the checks instead as you suggest. Thanks

MarkJ Over a year ago

@HiTech exactly, missing params are added at compile-time

Collectives™ on Stack Overflow

String default parameter value issue after conversion from VB6 to VB.Net

My question is:

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

My question is:

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related