[Mono-dev] Interop with Native Libraries Question

[Sebi Onofrei]

Hello everyone.

Please help me translating one function in the correct way

I have a library from which I have to use some methods which is written 
in C++.

The method I need to correctly translate is this:
*integer method_name(const void* a_handle, char* name, int* length)*

Now, what I tried looks like this:
*        [DllImport (libraryName, EntryPoint = "method_name", CharSet = 
CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
        private static unsafe extern integer EXT_method_name(void* 
handle, out string name, out int length);*

when I test the code I receive an integer that informs me that I 
delivered Invalid parameters

Next I tried  this:
*        [DllImport (libraryName, EntryPoint = "method_name", CharSet = 
CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
        private static unsafe extern integer EXT_method_name(void* 
handle, StringBuilder name, ref int length);*
this doesn't work either

Then I tried this:
*        [DllImport (libraryName, EntryPoint = "method_name", CharSet = 
CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
        private static unsafe extern integer EXT_method_name(IntPtr 
handle, StringBuilder name, out int length);*
and this doesn't work either :(


I have a similar method which works and looks like this:
*integer method_name(const void* a_handle, int* length)

*And my working "translation" is this:
*        [DllImport (libraryName, EntryPoint = "method_name", CharSet = 
CharSet.Auto, CallingConvention = CallingConvention.StdCall)]
        private static unsafe extern integer EXT_method_name(void* 
handle, out int length);*


Any ideas about what I did wrong? I'm a total newbie with Interop 
communication :)

I understood correctly that when I pass strings as parameters to that 
external method I have to Marshal them, but when I need strings as 
output... how
should I do this?

In mono's wiki there is an example with StringBuilder (the strncpy 
example), but either I did something wrong or some different approach is 
needed.


Thank you for all your efforts in helping me


With kind regards,
Sebastian
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