How to pass string by reference?

[gpetrou]

I have the following simple method

void Test(char* output)
{
   output = strdup("This is a test");
}

How can I make the generator produce something like:

internal static extern void Test_0(global::System.IntPtr instance, out string output);

Currently it produces something like:

internal static extern void Test_0(global::System.IntPtr instance, sbyte* output);

and if you add the following line to Preprocess

ctx.SetMethodParameterUsage("Foo", "Test", 1, ParameterUsage.Out);

it will produce

internal static extern void Test_0(global::System.IntPtr instance, out sbyte output);

[tritao]

It will only assume that it's a string with const char* types.

[gpetrou]

Is it possible to add something to Preprocess method to solve this?
Something that would do the following:

internal static extern void Test_0(global::System.IntPtr instance, out IntPtr output);

and

public void Test(out string output)
{
    IntPtr arg0;
    Internal.Test_0(__Instance, out arg0);
    output = Marshal.PtrToStringAnsi(arg0);
}

I guess I would need to add another function to the native class to free the allocated memory.

[tritao]

Something like this should in theory already be possible, using the ParameterUsage enum. You can try setting the parameter usage as ParameterUsage.Out using the SetMethodParameterUsage helper method in ASTContext.

Not sure how CppSharp will handle memory management in that case, but let me know if we need any improvements in that case.

[gpetrou]

I already tried to do that and it produces

out sbyte

instead of

out string

which is expected. So can I do something to overcome this?

[oysteinkrog]

What happens if you set the parameter type qualifier to be const?