Implicit array length with C# PInvoke

Question

Given the following C API:

void foo(const char ** stringArray, size_t arrayCount);

I want to create a PInvoke adapter for it in C#. I can make a one-to-one mapping in C# as:

[DllImport("x.dll", ...)]  // char set, etc. omitted
public static extern void foo(string[] stringArray, int arrayCount);

I'd like an implicit second parameter.

// Psuedo-code
[DllImport("x.dll", ...)]
public static extern void foo(string[] stringArray, 
                              [MarshalAs(stringArray.Length)] int arrayCount);

Obviously the [MarshalAs()] part is made-up.

The goal is for the C# calling code to look like this:

string[] list = { "x", "y" };
foo(list);

I can make a simple wrapper around the PInvoke, but I was wondering if that is the best way, or if my PInvoke declaration can directly solve?

p.s.w.g · Accepted Answer · 2013-08-01 14:50:57Z

3

Just create a wrapper function:

private static extern void foo(string[] stringArray, int arrayCount);

public static void foo(string[] stringArray) {
    foo(stringArray, stringArray.Length);
}

This is a far easier and more flexible solution.

answered Aug 1, 2013 at 14:50

p.s.w.g

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1 Comment

Sam Harwell Over a year ago

Don't forget [MarshalAs(UnmanagedType.LPArray, ArraySubType = UnmanagedType.LPStr)]

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