calling dll written in C

Hello,
I have an issue calling a dll written in C. The function I require expects a string parameter and passes another string back:

char * Plc_genpass(char *);


however when I call the function from VB it crashes my application:


Declare Function Plc_genpass Lib "u4ntpgen.dll" ( _
ByVal ls_string As String) As String


Can anyone point me in the right direction?


Thnaks

Tony.

Thanks FantCool,
I had the C code modified, and set the function prototype in VB to your suggestion. This again caused a crash.
I then initialised the return string to 60 spaces in case C had an issue with an uninitialised string. Same result, crash.

I am presuming the return string is contained in ret_string, and this will be found at the address located by the returned long, is this right?


Thanks again.

Tony.

Fant,
it returns an error reading a particular address then allows me to stat VC++ to debug. The information presented in VC++ is meaningless to me.

Your function prototype returning the long, can you explain why this was not set up as a sub, since ret_string's address would be known to VB. i.e.

Declare sub Plc_genpass Lib "u4ntpgen.dll" ( _
ByVal ls_string As String, ByRef ls_result As String)

Thanks

Tony.

Ok Fant,
I will relook at the dll, thanks for the help.

much appreciated.

Tony,