How to return text from Native (C++) code

Question

I am using Pinvoke for Interoperability between Native(C++) code and Managed(C#) code. What i want to achieve is get some text from native code into my managed code. For thi

Answer 1

If you're returning a char *, and don't want to have to modify the C/C++ code to allocate memory for your return value (or you can't modify that code), then you can change your C# extern function-prototype to return an IntPtr, and do the marshaling yourself.

For instance, here's a snippet of the interop I wrote for Pocketsphinx:

[DllImport("sphinxbase.dll", CallingConvention = CallingConvention.Cdecl)]
private static extern IntPtr /* char const * */ jsgf_grammar_name(IntPtr /* jsgf_t * */ jsgf);

And here's the get-accessor for the C# JsgfGrammar class. m_pU is an IntPtr that points to the raw jsgf_t object.

public string Name
{
    get
    {
        IntPtr pU = jsgf_grammar_name(m_pU);
        if (pU == IntPtr.Zero)
            strName = null;
        else
            strName = Marshal.PtrToStringAnsi(pU);
        return strName;
    }
}

Modifying this example for other string formats (e.g. Unicode) should be trivial.