ASCII string for interop?

[Bill Cohagan]

I'm trying to call an ActiveX dll via interop, but it expects a ref string
argument. Of course I can call it foo(ref strData), but this passed a
unicode string if strData is of type "string". I can convert to byte [],
but can't pass that as foo expects ref string.

So, how do I go about converting from unicode to ASCII (or UTF8), but still
pass something of string type?

Thanks in advance,
Bill

 

[Chris A. R.]

Something along these lines,

([MarshalAs(UnmanagedType.LPStr)]
string strData;

Check out Marshalling, MarshalAs, and the UnmanagedType Enumeration for more
details. Also check out the SizeConst parameter for fixed size strings.

<From Microsoft: "Default Marshaling for Strings">
UnmanagedType.BStr A COM-style BSTR with a prefixed length and Unicode
characters.
UnmanagedType.LPStr A pointer to a null-terminated array of ANSI
characters.
UnmanagedType.LPTStr A pointer to a null-terminated array of
platform-dependent characters.
UnmanagedType.LPWStr A pointer to a null-terminated array of Unicode
characters.
UnmanagedType.ByValTStr A fixed-length array of characters; the array's type
is determined by the character set of the containing structure.
</From Microsoft: "Default Marshaling for Strings">

Chris A.R.

 

[Joe Mayo [C# MVP]]

I'm trying to call an ActiveX dll via interop, but it expects a ref string
argument. Of course I can call it foo(ref strData), but this passed a
unicode string if strData is of type "string". I can convert to byte [],
but can't pass that as foo expects ref string.

So, how do I go about converting from unicode to ASCII (or UTF8), but still
pass something of string type?

Hi Bill,

I believe a StringBuilder should work in place of the string.

Joe

 

[Willy Denoyette [MVP]]

ActiveX dll in general use BSTR as strings and these are unicode strings,
just like CLR strings, so the COM interop marshaler should be happy to
handle this automaticaly.

Willy.