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Using LabView.dll in c# , cannot get string value from dll

mark4262 asked
Last Modified: 2008-01-09
I am trying to use a dll in my c# code that was generated by labview ...
The method returns version information for the dll
I get back values for everything but the string (addlInfo)
I know on the labview side that the string is 18 characters long.
When I make the call, addlInfoLen changes from 20 to 18, but I get an empty string for addlInfo???
PS - Also when, i try to relase the pointer, I get an "Invalid pointer" error.

From LabVIew:
void __cdecl esrInfo(float *verNo, long *buildYear, long *buildMonth, long *buildDay, char addlInfo[], long *addlInfoLen);

From C#
Use dllimport
       EntryPoint = "esrInfo",
       ExactSpelling = true,
       CharSet = CharSet.Ansi,
       CallingConvention = CallingConvention.Cdecl)

        public static extern /*unsafe*/ void esrInfo(
             out float verNo,
             out Int32 buildYear,
             out Int32 buildMonth,
             out Int32 buildDay,
             out IntPtr addlInfo,
             out Int32 addLength);

Call it
  public string GetVersion()
            //IntPtr ptr = new IntPtr();
            System.Single verNo = 1.0F;
            Int32 buildYear = 0;
            Int32 buildMonth = 0;
            Int32 buildDay = 0;
            IntPtr addlInfo = Marshal.AllocHGlobal(20);
            Int32 addLength = 20;
            IntPtr newPointer = IntPtr.Zero;

            addlInfo = IntPtr.Zero;
            //string temp = "";
                esrInfo(out verNo,
                     out buildYear,
                     out buildMonth,
                     out buildDay,
                     out addlInfo,
                     out addLength);

                Marshal.ReAllocHGlobal(addlInfo, newPointer);
               StringBuilder addInfo = new StringBuilder( Marshal.PtrToStringAnsi(newPointer));


            catch (Exception ex)
            //addnInfo = ptr.ToString();

            //temp = addnInfo.ToString();
            if (verNo > 0.0) return string.Format("Version: {0} Build(YYYYMMDD):{1}{2}{3}",verNo.ToString(), buildYear.ToString(), buildMonth.ToString(),buildDay.ToString());
            return "0.0";


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