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Passing A String From C++ To A C Dll

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I hope that this is not 'too simple' for anyone replying, but I'm a C novice so your advice will be most appreciated.


The background is that I'm trying to learn about DLLs and using them in a Windows 7 environment.


I have created a simple 'HelloWorld-ish' DLL in C which compiles OK.  It is meant to receive a string passed to it from a calling C++ program and display that string in a messagebox.


I am aware that strings are handled differently in C and C++.  I suspect that my 'caller' program is passing the string OK but that my C DLL is not handling it OK.  The DLL displays just the first character of the passed string.


Here's the code from the DLL - first the dll.h:

#ifndef _DLL_H_
#define _DLL_H_
# define DLLIMPORT __declspec (dllexport)
#else /* Not BUILDING_DLL */
# define DLLIMPORT __declspec (dllimport)
#endif /* Not BUILDING_DLL */

DLLIMPORT void HelloWorld (char *str_in);

#endif /* _DLL_H_ */

And the HelloWorld.c code:

#include "E:/documents/C_PlusPlus/HelloWorld_C/dll.h"
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
DLLIMPORT void HelloWorld (char *str_in)
    MessageBox (0, str_in, "Try 2", MB_ICONINFORMATION);

BOOL APIENTRY DllMain (HINSTANCE hInst     /* Library instance handle. */ ,
                       DWORD reason        /* Reason this function is being called. */ ,
                       LPVOID reserved     /* Not used. */ )
    switch (reason)
    /* Returns TRUE on success, FALSE on failure */
    return TRUE;

My environment in this context is Windows 7 64 bit and Dev-C++


I have scoured the Internet and forums but I can't seem to find what I'm looking for.


Any advice will be most appreciated and thank you in anticipation.



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