Passing an fstream (or equivalent) from C# to C++ through CLI

Question

How can I pass an fstream or equivalent from C# through CLI to an unmanaged C++ DLL?

Rough application outline:

• C# application reads a binary file from a database
• Unmanaged C++ dll is used to "decode" this file and return the information contained therein
• I can modify any of the C# code. The CLI wrapper is the only portion of the C++ side that I can modify.

I'm currently saving the binary file to disk and passing the path of it to the CLI wrapper where it is opened as an fstream. This is fine for test purposes, but won't work for production for obvious reasons.

I've also looked into passing a byte array to the DLL but I was not able to find a way to convert that to an fstream other than with GlobalAlloc, which I would prefer not to use.

Any help or ideas would be appreciated.

Thanks.

Answer 1

You can pass a managed binary array to the C++/CLI DLL. Pin the array. This can then be converted to an STL string object. You can then pass the STL string into an STL stringstream object, which inherits from iostream. Think of stringstream as a .NET MemoryBuffer object. Pass stringstream to your unmanaged C++. That can probably be done in < 10 lines of code. The downside is the data will get copied in memory which is inefficient. For many applications I doubt it would be an issue.

Alternatively, you could write your own class inheriting from stream_buffer that wraps a .NET stream object. (Better to inherit from this instead of iostream, as others propose). That would be the most efficient way because no memory would be needlessly copied but I wouldn't bother doing it if the first method is fast enough.