Returning string from DLL

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Hakon - 25 Nov 2003 10:10 GMT

Hello,

I need to call a function in a legacy, unmanaged DLL that
has the following syntax:
int GetVersion(char **version);

The 'version' parameter needs to be a pre-allocated string
of size 250 and it will be filled by the function. The
function both zero-terminate the version string as well as
return the length of the version string.

I have tried several approaches - all with exceptions or
no data returned. Can anyone help me out with a way to
call this function from C#?

I think the behaviour is related to some legacy VB6
integration....

Thanks in advance,
Hakon

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Jens Thiel - 25 Nov 2003 10:57 GMT

> I need to call a function in a legacy, unmanaged DLL that
> has the following syntax:
[quoted text clipped - 4 lines]
> function both zero-terminate the version string as well as
> return the length of the version string.

I would try something like

[ DllImport("Unmanaged.dll", CharSet=CharSet.Ansi, ExactSpelling=true) ]
private static extern void GetVersion(StringBuilder buf);

and pass a StringBuilder with a capacity of at least 250 characters.

Jens.

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- 25 Nov 2003 11:26 GMT

Well, I have been down that road and it does not work :(

A snip of my C# code:
[DllImport("MyGetVersion.dll", CharSet=CharSet.Ansi,
ExactSpelling=true)]
private static extern int MyGetVersion(StringBuilder
version);

private static void Test()
{
    StringBuilder version = new StringBuilder(250);
    MyGetVersion(version);
    System.Diagnostics.Debug.WriteLine(version);
}

I have created my own unmanaged DLL to try a few things
out and the MyGetVersion function looks like this:

extern "C" MYGETVERSION_API int MyGetVersion(char
**version)
{
    char *target = *version;
    strncpy(target, "Version 1.1", 249);
    return (int) strlen(target);
}

Calling the C++ from C# gives me an access denied error...

Thanks,
Hakon

>-----Original Message-----
>> I need to call a function in a legacy, unmanaged DLL that
[quoted text clipped - 14 lines]
>
>Jens.

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Mattias Sj?gren - 25 Nov 2003 12:10 GMT

Hakon,

>A snip of my C# code:
>[DllImport("MyGetVersion.dll", CharSet=CharSet.Ansi,
>ExactSpelling=true)]
>private static extern int MyGetVersion(StringBuilder
>version);

Make the StringBuilder a ref parameter to add the extra level of
indirection needed.

private static extern int MyGetVersion(ref StringBuilder version);

Mattias

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Mattias Sjögren [MVP] mattias @ mvps.org
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- 25 Nov 2003 12:45 GMT

Hehe - I was sure that I tried that before but now it
works :D

Thanks Mattias and Jens

/H

>-----Original Message-----
>Hakon,
[quoted text clipped - 11 lines]
>
>Mattias

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Returning string from DLL

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