Creating a DLL, confusion with __declspec(dllexport)

Visual Studio C++ 2005
Windows XP

I am creating this DLL library. The DLL actually links with another LIB. I have included the headers and lib path. Everything compiles ok.

Actually, this code I wrote for running on linux, which runs ok. Now I am porting it to run on windows.

However, I have noticed that some DLL from some code samples use this开发者_运维技巧 in there header file:

static __declspec(dllexport) float some_function(int num1, int num2);

However, I have done the following, sample code below for the header *.h file. However, not sure if I still need the above or not?

#ifdef __cplusplus
extern "C" {
#endif

media_t* get_media(media_description_t* obj);
void* get_item(media_description_list_t *obj, int num);
int get_number_format(media_t *obj);
const char* get_media_value(media_t *obj);

#ifdef __cplusplus
}
#endif

Sample code for for implementation *.cpp file

int get_number_format(media_t *obj)
{
    Media *med = (Media*)obj;
    return med->getNumFormat();
}

So, do I need this static __declspec(dllexport)?

Many thanks for any advice,

The linker needs to be told which of your functions should be exported, making them usable by other code that uses your DLL. __declspec(dllexport) does this. But you can also do it by providing the linker with a .def file, a list of exported function names. Somewhat painful because it now is up to you to keep that file in sync with your code. Docs are here.

__declspec(dllexport) adds the function to the DLL's export table. This table is a convention that allows a process wishing to use the DLL to correctly call the function.

There are other ways to export functions from DLLs, but this one is probably the more modern and easier to use.

yes it is needed, if you don't have the dllexport the function will not be accessible in any other application where you are calling that function.

If you put the implementation of a method in the h file, you don't need to use the __declspec(dllexport) declaration.