Convert VB.NET To C#.NET

There is a code in VB.NET. The code utilizes some vendor made API by declaring Lib functions.

A function will pass a parameter and the result will save in the parameter.



Here is how we use it:


If I use Msgbox "[" + strGMW_DB_Read_Buf + "]", it prompts


Look, the last bucket misses.

However, the above needed to be converted to C#. My conversion is like:





The value of strGMW_DB_Read_Buf is still empty!

If I change the declaration


There will be an unknown runtime error.

What should I do? Please help.

in VB.NET you should use & to concat 2 strings, + is used in C#

If it were the operator, then the first square bracket concatenation wouldn't have worked. I think the buffer contains a null-terminated string, so it gets to the null and stops and doesn't display the closing bracket.

stanley1610:
Set a BreakPoint in your VB.NET version and carefully go one step at a time, observing in the Locals window (or by hovering your mouse cursor over variables) the actual runtime values of the strings.

In C#, you would be able to see "[the result\0]", because when displaying runtime string values, quotes are added to denote a string. However, in VB.NET, there is a different clue. For a normal string, quotes would be added to the beginning and end. So "[the result]" would show in the Locals window as "[the result]". If there is a null character just before the end bracket, VB.NET won't display it as \0 the way C# does, but it also won't show the rest of the string, including the end quote that it adds. It would appear as "[the result instead of "[the result". Every other string value would have two quotes in the Locals window, but one with a null character would have only the beginning quote.

One possible reason your C# buffer is always empty is that in your VB.NET version, you set it to a string of 41 spaces, but the C# version is just an empty string. You didn't rewrite it in the same way.

Thanks a lot for your reply.

Yes, my guess is similar to your opinion. The result might be result\0 instead of result, therefore the output cannot show the characters following \0.

However, my task is to make C# code work. I try to declare the string with the value of 41 spaces
(i.e. " "

It does not work either. I think it relates to pass by reference but it prompts runtime error. How can I rewrite it?

Many thanks.

I had an idea....

There is this program called Reflector that allows one to open an assembly and view the MSIL and structure and everything. It can also translate the MSIL into [mostly] equivalent VB.NET or C#.

So I grabbed an old VB.NET project, added a module, and pasted this in it:
Then I compiled and opened the assembly in Reflector and viewed the C# version, which goes like this:
Then I found this article. Search for "UnmanagedType.VBByRefStr" on the page, and read some of the stuff in the section called Learn the Ins and Outs. It turns out that VB.NET automatically changes ByVal argname As String to something completely different. You may have to MarshalAs(UnmanagedType.LPTStr) instead, or you may simple need to have both as ref arguments.

Please read more here and here.

First try making both ref parameters. The default marshaling is as UnmanagedType.BStr. If that doesn't work, you can try UnmanagedType.LPTStr or UnmanagedType.VBByRefStr.

Just add one piece at a time until it works.

Many thanks for your reply. Your code can work.

However, when I prompt the variable:

Console.WriteLine("strGMW_DB_Read_Buf:[" + strGMW_DB_Read_Buf.Trim() + "]");

The result string cannot be trimmed by Trim(). Is it due to UnmanagedType? How can I turn it back to normal string?

Thanks for your help

Have you tried assigning it to a new [normal] String variable?

strGMW_DB_Read_Buf.SubString(0, 20).Trim();

So you added a call to Substring(). Did it work, did it not work? I'm not telepathic.

I would guess not. If it's still just character buffer there's not substring method, and C# isn't one to do implicit conversions for you...