P/Invoke help with C# declaration of C function char * func(const char *)

[Ted Sung]

Hi,

I'm trying to call a C function from a DLL. The C function is
declared as

char * function( const char * )

I'm declaring it in C# as follows:

[DllImport(@"d:\ mywork\csharp\t estsubs\cmosub3 2.dll")]
public static extern string icmo_version_ch k(
[MarshalAs(Unman agedType.LPStr)]
string version );
and using it as follows:

string sTestVersion = "3.0f_p2";
string sVersion = icmo_version_ch k( sTestVersion );

I get an exception: System.NullRefe renceException ... Object reference
could not set to an instance of an object.

What am I doing wrong? Is it the string icmo_version_ch k? If so,
what should I use.

Thanks,

Ted

[Ken Onweller \(.NET MCSD\)]

Adam Nathan wrote a book called ".NET and COM, The Complete Interoperabilit y
Guide" which
can help with EVERYTHING you ever need to know regarding using COM and
Native libraries.

Nonetheless, you might want to try doing this instead...

[DllImport(@"d:\ mywork\csharp\t estsubs\cmosub3 2.dll")]
public static extern String icmo_version_ch k(
String version );

"Ted Sung" <te**@intex.com > wrote in message
news:86******** *************** **@posting.goog le.com... Hi,

I'm trying to call a C function from a DLL. The C function is
declared as

char * function( const char * )

I'm declaring it in C# as follows:

[DllImport(@"d:\ mywork\csharp\t estsubs\cmosub3 2.dll")]
public static extern string icmo_version_ch k(
[MarshalAs(Unman agedType.LPStr)]
string version );
and using it as follows:

string sTestVersion = "3.0f_p2";
string sVersion = icmo_version_ch k( sTestVersion );

I get an exception: System.NullRefe renceException ... Object reference
could not set to an instance of an object.

What am I doing wrong? Is it the string icmo_version_ch k? If so,
what should I use.

Thanks,

Ted