Char in VC and String in VB ???

tranhung · February 14th, 2004, 11:21 PM

Hi Everybody
when i write DLL in VC
Code:
Void __stdcall WGS84TOVN99( char inStr[100], int j, char outStr[100] );
{
// Some command
}
I call it in VB:

Public Declare Function WGS84TOVN99 Lib Path+"\.dll" (ByRef InputLine As String, ByVal i As Long, outputLine As String)
Dim inStr as String
instr="My input String"
Dim outStr as String
Call WGS84TOVN99(inStr,1,outStr)
But when I debug in VC inStr not correct, that why program dump.
Can you help me
Thanks

nikolai · February 16th, 2004, 03:19 PM

I think you need to use the BSTR type for strings in C/C++. BSTR is a Binary-Safe Unicode string. The length of the string is encoded in the first couple bytes of the string. That means that you can't use a fixed-size character array.

chars are 1-byte. Unicode (wide) characters are two bytes.

The string "Hello" as a char array will look like this (byte representation in hex):

Code:

 48  65  6c  6c  6f   00   00   00   00  ...  00
  |   |   |   |   |    |    |    |    |        |
 'h' 'e' 'l' 'l' 'o' '\0' '\0' '\0' '\0' ... '\0'

The same string as a BSTR will look like this:

Code:

00 00 00 05 00 48 00 65 00 6c 00 6c 00 6f
\_________/ \___/ \___/ \___/ \___/ \___/
 (length)    'H'   'e'   'l'   'l'   'o'

Take care,

Nik
http://www.bigaction.org/