Unmanaged code call, array parsing

Question

I'm working with the game Arma 3 where you can write your own Extensions (means a C++ or C# library). These Extensions have a defined entry point which is this DLL interface

void __stdcall RVExtension(char *output, int outputSize, const char  *function);
int __stdcall RVExtensionArgs(char *output, int outputSize, const char *function, const char **args, int argCnt);

When implementing this into C# the entry point for RVExtension would be

[DllExport("_RVExtension@12", CallingConvention = CallingConvention.Winapi)]
public static void RvExtension(StringBuilder output, int outputSize,
    [MarshalAs(UnmanagedType.LPStr)] string function)
{
    output.Append("Foo");
}

I'm using this library for the DLLExport.

As the entry point for RVExtensionArgs is quite new I wanted to implement it aswell. My solution so far is this one here:

[DllExport("_RVExtensionArgs@20", CallingConvention = CallingConvention.Winapi)]
public static int RvExtensionArgs(StringBuilder output, int outputSize,
    [MarshalAs(UnmanagedType.LPStr)] string function, [MarshalAs(UnmanagedType.LPArray)] string[] args,
        int argCount)
{
    output.Append("Foo");
}

In general this works however the array passed for the args argument is not converted properly. You only get the first element of the passed array.

I tried to define the LPArray SizeConst property but this has to be a fixed size I can't provide. The passed array elements can be up to 1024. Plus I got an MarshalException when accessing the DLL with my test console.

How can I fix this behaviour?

Ok, well this was quite too easy. Will you post this as an answer, just for the completeness? — Christian Klemm
– Christian Klemm, Commented Feb 20, 2017 at 13:23

Christian Klemm · Accepted Answer · 2017-04-20 12:23:29Z

1

Just for the completeness, here is the solution as proposed by Hans Passant.

public static int RvExtensionArgs(StringBuilder output, int outputSize,
        [MarshalAs(UnmanagedType.LPStr)] string function,
        [MarshalAs(UnmanagedType.LPArray, ArraySubType = UnmanagedType.LPStr, SizeParamIndex = 4)] string[] args,
        int argCount)
{
    output.Append("Foo");
}

answered Apr 20, 2017 at 12:23

Christian Klemm

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