Typedef and more

[NicholasCougar]

Hi: I encount such codes, plz explain them in detail. Thank you in advance.:rose: typedef unsigned (WINAPI *PBEGINTHREADEX_THREADFUNC)(LPVOID lpThreadParameter); typedef unsigned *PBEGINTHREADEX_THREADID; Best regard. I confess that I am a stubborn guy, but why not put things thoroughly, logically and systematically clean. One concrete prolem is worth a thousand unapplied abstractions.

[Christian Graus]

A typedef allows a new parameter to be created, it's more intelligent than a macro ( I believe ) but does the same sort of thing in effect. In this case, for example, PBEGINTHREADEX_THREADID is the same as an unsigned (int) pointer. The reason to do this is that the type you use through your code for something specific can be changed just by changing the typedef. I've never found a use for them, so if anyone else contradicts me, believe them first :-) Christian The tragedy of cyberspace - that so much can travel so far, and yet mean so little. "I'm somewhat suspicious of STL though. My (test,experimental) program worked first time. Whats that all about??!?! - Jon Hulatt, 22/3/2002

[Rickard Andersson20]

NicholasCougar wrote: typedef unsigned (WINAPI *PBEGINTHREADEX_THREADFUNC)(LPVOID lpThreadParameter); function pointer NicholasCougar wrote: typedef unsigned *PBEGINTHREADEX_THREADID; a typedef of a unsigned! :) A typedef is a way to make your own names of types in C++. And sometimes "makeing" your own types... ------------------------------------ Rickard Andersson, Suza Computing ICQ#: 50302279 I'm from the winter country SWEDEN! ------------------------------------

[Rickard Andersson20]

so my answer could be wrong? :-O ------------------------------------ Rickard Andersson, Suza Computing ICQ#: 50302279 I'm from the winter country SWEDEN! ------------------------------------

[Lakitu]

Hi, the first defines a pointer to a function that takes a void pointer as parameter and returns an unsigned. The second simply defines PBEGINTHREADEX_THREADID to be a pointer to an unsigned. You probably got this from the CreateThread API, right? ;)

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You know, for kids!

[Christian Graus]

I thought my answer might be a little more expansive, but I didn't think yours was wrong. Christian The tragedy of cyberspace - that so much can travel so far, and yet mean so little. "I'm somewhat suspicious of STL though. My (test,experimental) program worked first time. Whats that all about??!?! - Jon Hulatt, 22/3/2002

[Rickard Andersson20]

Of course! :rolleyes: And I just wanted to know if I was wrong about that point! :) ------------------------------------ Rickard Andersson, Suza Computing ICQ#: 50302279 I'm from the winter country SWEDEN! ------------------------------------

[Roger Allen]

I have used this kind of typedef in the past. Usually when I have loaded a DLL dynamically, and you nned to store function pointers to the return calls from GetProcAddress. This allows you to save the pointers in member vars and call them like function of a regular class once the pointers are correctly initialised. For example:

typedef int (*DLLINIT)(int x);
typedef void (*DLLEXIT)() ;

class DLLWrapper
{
DLLINIT DLLInit;
DLLEXIT DLLExit ;
HINSTANCE hInstance ;

DLLWrapper(CString& filename)
	{
	DLLInit = NULL ;
	DLLExit = NULL ;
	hInstance = NULL ;
	LoadDll(filename) ;
	} ;
~DLLWrapper()
	{
	if (hInstance)
		FreeLibrary(hIstance) ;
	hInsatnce = NULL ;
	}

bool		LoadDLL(CString& filename)
{
hInstance = LoadLibrary(filename);
if (!hInstance)
	return false ;

DLLInit = (DLLINIT)GetProcAddress(RefinementDLL.pDLL, "DLLInit");
DLLExit = (DLLEXIT)GetProcAddress(RefinementDLL.pDLL, "DLLExit");
return true ;
}

} ;

// you can use the object like this
DLLWrapper fred("Some.DLL") ;

fred.DLLInit(1) ; // call through typedef pointer

That lot was put together quickly, so it may not all be 100% correct. Roger Allen Sonork 100.10016 If I'm not breathing, I'm either dead or holding my breath. A fool jabbers, while a wise man listens. But is he so wise to listen to the fool?

[NicholasCougar]

The codes are from Multithreading Applications in Win32 written by Jim Beveridge & Robert Wiener First, please study the second and sixth parameters. unsigned long _beginthreadex( void *security, unsigned stack_size, unsigned (* start_address)(void *), void *arglist, unsigned initflag, unsigned *thrdaddr); HANDLE CreateThread( LPSECURITY_ATTRIBUTES lpThreadAttributes, DWORD dwStackSize, LPTHREAD_START_ROUTINE lpStartAddress, LPVOID lpParameter, DWORD dwCreationFlags, LPDWROD lpThreadId); According to Jim Beveridge & Robert Wiener' point of view, the function _beginthreadex() is the coat of CreateThread() and the types of its parameters have been changed for the sake of being adoptable to other operation system. While, as the CloseHandle() must be called at last, programmers can't get rid of "window.h". Another side effect is, though C compiler makes no difference between DWORD and unsigned (in fact unsigned int), C++ compiler doen't think so. As CreateThread() is inside _beginthreadex(), its parameters are less likely to be modified. Defining parameters according to CreateThread() is smarter. Since the parameters must be accepted by _beginthreadex(), the codes we discussing must appear there. The true meaning of the codes is: force type convertion before calling _beginthreadex(). the following are codes in all: //The beginning of codes #define WIN32_LEAN_AND_MEAN #include #include #include #include typedef unsigned (WINAPI *PBEGINTHREADEX_THREADFUNC)( LPVOID lpThreadParameter ); typedef unsigned *PBEGINTHREADEX_THREADID; int main() { HANDLE hThread; DWORD dwThreadId; int i=0; hThread = (HANDLE) _beginthreadex(NULL, 0, (PBEGINTHREADEX_THREADFUNC)ThreadFunc, // Attention, Plz (LPVOID) i, 0, (PBEGINTHREADEX_THREADID) & dwThreadId // Attention, Plz ); if(hThread) { WaitForSingleObject(hThread, INFINITE); CloseHandle(hThread); } return EXIT_SUCCESS; } DWORD WINAPI ThreadFunc(LPVOID n) { // Do something... return 0; } //The end of codes My opinion