[Mono-list] InteropServices: DllNotFoundException...?

[Simon Ask Ulsnes]

Thank you, that seems good.
Having always programmed Managed, I'm not really used to C-style memory 
management (or memory management at all, actually). ;-)

This will certainly help.

- Simon

Jonathan Pryor wrote:

>On Sun, 2004-05-23 at 11:37, Simon Ask Ulsnes wrote:
>  
>
>>*sigh*
>>Hooray for Managed Code! ;-)
>>
>>Could you please give a short example of a C++ library function that 
>>returns a string for use in a managed application? (with proper memory 
>>hygiene ;-)
>>    
>>
>
>Sure.  I haven't tried to compile any of this, but it's the right
>idea...
>
>	//
>	// Unmanaged C++ code
>	//
>
>	#include <string>
>	#include <stdlib.h>
>
>        /** 
>         * To minimize library differences, this function should be used
>         * by "external" code (managed code, other 3rd party code) to 
>         * free memory allocated within this library.
>         *
>         * This is particularly important on any platform that has 
>         * multiple runtime libraries which each export "free" (say, 
>         * Windows, with MSVCRT, GCC, Borland, and lots of other C 
>         * runtime library implementations, all of which are 
>         * mutually incompatible).
>         */
>        extern "C" void
>        mylib_free (void* mem)
>        {
>        	free (mem);
>        }
>        
>        /**
>         * This is a function which returns a newly allocated string.
>         * Callers *must* use mylib_free() to free the returned memory.
>         */
>        extern "C" char*
>        mylib_get_string ()
>        {
>        	std::string s ("this is my string");
>        	// manipulate `s' to fill its contents
>        
>        	// paranoia: check for integer overflow in buffer size 
>        	// calculation.  Consider if s.size() is = 0xFFFFFFFF.
>        	// 0xFFFFFFFF + 1 = 0, which is too small to hold the 
>        	// required string; any attempt to fill the buffer would
>        	// result in memory corruption.
>        	// Yes, this is likely absurd, as your app would likely
>        	// have crashed by now if it had a string that big, but
>        	// better safe than sorry.
>        	// For more information, see:
>        	// http://msdn.microsoft.com/security/securecode/columns/default.aspx?pull=/library/en-us/dncode/html/secure04102003.asp 
>        	std::string::size_type size = s.size();
>        	if (size + 1 <= size) return NULL;
>        	size += 1;
>        
>        	// return newly allocated string.
>        	char *r = (char*) malloc (size);
>        	if (!r) return NULL;
>        	strcpy (r, s.c_str());
>        	return r;
>        }
>        
>        //
>        // Managed code
>        //
>        
>        using System;
>        using System.Runtime.InteropServices;
>        
>        class Mylib {
>        	[DllImport ("mylib")]
>        	private static extern void mylib_free (IntPtr r);
>        
>        	[DllImport ("mylib")]
>        	private static extern IntPtr mylib_get_string ();
>        
>        	public static string GetString ()
>        	{
>        		IntPtr r = mylib_get_string ();
>        		if (r == IntPtr.Zero) return null;
>        		string s = null;
>        		try {
>        			s = Marshal.PtrToStringAnsi (r);
>        		}
>        		finally {
>        			mylib_free (r);
>        		}
>        		return s;
>        	}
>        }
>
> - Jon
>
>
>
>
>  
>