Question

I have an third part dll that have a function that returns a string. When I call the function I got for example ‘123456’ back. At least it seams like that, but when i do mystring.length it does not return any length. If I set the text property of a label it shows ‘123456’.

When I have the string I got from the dll I send it to a webservice function:

rem call dll and get string dim mystring as string=mydll.getstring()  rem Send it to the webservice webservice.SaveString(mystring)  

The webservice crashes with an webexeption (‘protocoll error’) when I send in the string I got from the dll. If I instead send it like this:

rem call dll and get string dim mystring as string=mydll.getstring()  rem Send it to the webservice dim FixedString as string = mid(mystring,1,6) webservice.SaveString(mystring)  

Then it works and everything is fine. That leads me to think that the string I got from the DLL is in someway not terminated correct. And I dont know how to fix it from vb.net (I cant change the DLL) and I dont know in beforehand how long the string will be.

The dll does only work on site when specific hardware is connected so I can’t sit at the office trying to fix this in dev-environment. So I would like to have some possibly solutions to this before I go to the customer again.

Edit 1: I tried to just do a loop that looped from 1 to 100 (because I dont know the real length) and tried to copy all characters that <>” to a new variable but it didnt work. I didnt try other variants because the day was over and I had to leave the customer site.

Edit 2:
The DLL Im talking to is made in VB6. That DLL is talking to other DLLs that is made in C++ (I think).

My program < – > vb6-DLL <-> c++-DLL <-> hardware

Answer 1

Check out the MSDN documentation about strings, especially the part about:

In the .NET Framework, a String object can include embedded nulls, which count as a part of the string’s length. However, in some languages, such as C and C++, a null character indicates the end of a string, is not considered a part of the string, and is not counted as part of the string’s length. This means that the following common assumptions that C and C++ programmers or that libraries written in C or C++ might make about strings are not necessarily valid when applied to String objects:

The value returned by the strlen or wcslen functions does not necessarily equal String.Length.

The string created by the strcpy_s or wcscpy_s functions is not necessarily identical to the string created by the String.Copy method.

You should ensure that native C and C++ code that instantiates String objects, and code that is passed String objects through platform invoke, do not assume that an embedded null marks the end of the string.

Instead I’d do something like:

rem call dll and get string dim mystring as string=string.intern(mydll.getstring()) 

(Note: I haven’t tried this)