Interop: failure returning a value from unmanaged dll

[ConfNoob]

part 1: there is a NON - COM unmanaged dll in VC++ 6.0
BOOL function(char * name, int nOption)

part 2: there is a C# web service that has to consume the above DLL
used DLLImport to call the Non-COM Dll.
[DllImport("Dllname.dll", EntryPoint = "function",

used "Debug Unmanaged Code" to step into DLL.

the DLL gets the right values, processes the steps properly.

however when the value is returned to the C# Webservice
no matter if the return from the unmanaged DLL is TRUE (1) or FALSE
(0), the bool in the C# webservice is always 0/false

the DLL DOES return BOOL which is a 4 byte int , hence im led to
believe that it should be marshalled properly into a C# 'bool'

as alternatives have done the following.

- tried casting the BOOL to an int using Convert.ToInt32()

trying to convert the ENTIRE unmanaged DLL into a COM application is
not something i am able to do ....

suggestions ??

TIA

 

[Nicholas Paldino [.NET/C# MVP]]

ConfNoob,

You haven't shown the declaration of the function in C#. Can you
provide that?

Also, are you sure that the calling convention is correct?

 

[ConfNoob]

public static extern bool function(string name,int nOption);

is how its declared in C#

"CallingConvention = CallingConvention.StdCall"

is what i've specified in the DllImport()

thanks again

 

[Willy Denoyette [MVP]]

| public static extern bool function(string name,int nOption);
|
| is how its declared in C#
|
| "CallingConvention = CallingConvention.StdCall"
|
| is what i've specified in the DllImport()
|
| thanks again
|

Try this: declare the function to return an int and check for the value 0 or
!= 0.

public static extern int function(string name,int nOption);

....

if(function(string name,int nOption) != 0)
// function returned non 0 (TRUE) value
else
// function returned 0 (FALSE)

If this works, the bool version should work also.

Willy.

 

[Willy Denoyette [MVP]]

| public static extern bool function(string name,int nOption);
|
| is how its declared in C#
|
| "CallingConvention = CallingConvention.StdCall"
|
| is what i've specified in the DllImport()
|
| thanks again
|

Oh, and who guarantees that the function uses the stdcall convention?

Willy.

 

[ConfNoob]

thanks Willy for the replies.

will try those.

 

[ConfNoob]

hi Willy,

do you suggest that i make the change in the VC++ DLL to return an int
?

thanks again.

 

[Willy Denoyette [MVP]]

No, I just need to be sure the return type is a BOOL (which is typedef'd as
an int), so I like to see the value 0 for FALSE and !=0 for TRUE returned.
If this is true, the signature bool function(...) is correct and bool should
be true or false depending on the value of the int, however, if the C return
type is a bool (a byte), then the value of bool will always be fase as the
interop layer expects an int returned from C.

Willy.

| hi Willy,
|
| do you suggest that i make the change in the VC++ DLL to return an int
| ?
|
| thanks again.
|