Thread: dllexport of a structure

The only effect __declspec(dllexport) on a structure has is that it adds __declspec(dllexport) to every member function. Since the structure has no member functions, it should have no effect at all. (And in any case, you should have __declspec(dllimport) in the EXE version, and you should put the struct in a header with a macro for the declspec that switches appropriately.)
The __stdcall on the structure is simply wrong.

Then there's the other problems with your code. The EXE version calls the struct itself *and* the pointer typedef "CreatedWindowsPtr". The DLL version calls the struct and the variable "CreatedWindows". Finally, your memset in the EXE uses sizeof(CreatedWindows), but that picks up the size of the pointer, i.e. it's far too little to zero out the entire structure. Give all your entities distinct names, and you'll be far happier.
Also, have you actually checked the return value of GetProcAddress? Even under extern "C", I wouldn't be surprised if the compiler mangled the name of the variable such that importing "CreatedWindows" would fail to find anything.

yeah its true the function can't be found,i didn't managed this function with getlasterror before , it terminates with error 127 cant find function .
even its a struct and no function ?

anyway how should i pass data from dll to my process than?
i think about readprocessmemory or mapping memory to share ...
but was actually to lazy to search the msdn for those posibillitys, sorry

how to caluculate the startaddress of the struct?
ist it the BaseAdress of the proccess + the pointer address to the struct?
and if yes, are the values of the struct something like this?

Code:

sturct mystruct
{
WORD x;
DWORD y;
WORD z;
}

Code:

offset [structPointer];
offset [structPointer]+??bytes = WORD x
offset [structPointer]+??bytes+WORD=  DWORD y
offset [structPointer]+??bytes+WORD+DWORD=  WORD z

but how the struct looks like in binary?

Originally Posted by punkywow

yeah its true the function can't be found,i didn't managed this function with getlasterror before , it terminates with error 127 cant find function .
even its a struct and no function ?

The API function is called "get procedure address" and yet you can use it to get data. That's just the way it is; the assumption, because it is far more common, is that imported symbols are functions. This is reflected in the function name, return type, and error messages. That doesn't mean it won't work with data. It just means you need to use the correct name.
You're basically doing the right thing. But the name you type in the source code isn't necessarily the name internally visible in the DLL.

So let's see. First, do you have to load the DLL dynamically? It's easier to do a load-time link against the DLL. You do this like this:

Code:

// dllhdr.h: The interface of the DLL.
#ifndef GUARD_DLLHDR_H
#define GUARD_DLLHDR_H

#if defined(BUILD_MY_DLL)
#define DLLSYM __declspec(dllexport)
#else
#define DLLSYM __declspec(dllimport)
#endif

#if defined(__cplusplus)
extern "C" {
#endif

struct MyData
{
  /* Put data here. */
};

DLLSYM extern MyData myData;

#if defined(__cplusplus)
}
#endif

#endif /*guard*/

--------------------------------------
// dllimp.cpp: DLL implementation file
#define BUILD_MY_DLL
#include "dllhdr.h"
MyData myData;

-------------------------------------
// main.cpp: EXE implementation file
#include "dllhdr.h"

void init()
{
  memset(&myData, 0, sizeof(myData));
}

If you really want to load the DLL with LoadLibrary, it's more complicated.