C / C++ / MFC

Re: What is the difference between c++ structs and c# structs..?

21-Oct-08 18:58

Structs are used in both languages to encapsulate related variables.

Structs differ between C++ and C# in how they compare with classes.

In C#, a struct is a value type, while a class is a reference type.

In the managed world, there are value types, which can be and most often are
stored on the stack (or as a member of a class) and reference types which are always
allocated on a heap. In C#, a struct is a value type, while a class is a reference type.
This is an important concept in C# - for example, when you pass a struct as a function parameter,
it is passed by value, so if the function changes the struct, the original passed object is
untouched. When a class object is passed it is by reference, so any changes made by the function
change the original object. That difference is why C# doesn't need *, &, and -> operators all
over the place.

In the native C++ world, structs and classes are the same except for default
member access. Both can be allocated on the stack or the heap. Reference and
value are controlled by operators, like *, &, ., and ->

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

CPallini21-Oct-08 21:46

CPallini

21-Oct-08 21:46

And what is the difference between a C# class and a C++ one?
And what about the new keyword?
Hey, is there also any difference on the inheritance paradigm?
...
Big Grin | :-D

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

Re: What is the difference between c++ structs and c# structs..?

Iain Clarke, Warrior Programmer21-Oct-08 22:03

Iain Clarke, Warrior Programmer

21-Oct-08 22:03

Getting soft... I was expecting:

CPallini shoulda wrote:

About 3 characters.

Re: What is the difference between c++ structs and c# structs..?

CPallini21-Oct-08 22:05

CPallini

21-Oct-08 22:05

You're great.

Anyway, that's right: I feel a bit weak this morning.
Smile | :)

BTW welcome in the THHB.
(Official investiture on my blog [^].)

Help with code

dtaylor0121-Oct-08 15:46

dtaylor01

21-Oct-08 15:46

Can someone take a look at my code to see what I'm doing wrong.

int score;<br />
	 char grade =0;<br />
<br />
     // read in total score <br />
<br />
     cout << endl;<br />
     cout << "Enter total score (float, must be <= 100): "; <br />
     cin >> score;  <br />
     <br />
     if (score >= 85); <br />
        grade = 'A';<br />
	 else if (score >= 75); <br />
        grade = 'B';<br />
	 else if (score >= 65); <br />
        grade = 'C';<br />
	 else if (score >= 55);<br />
	    grade = 'D';<br />
	 else <br />
	    grade = 'F';<br />
	 End if // score >= 55<br />
     End if // score >= 65<br />
     End if // score >= 75<br />
     End if // score >= 85<br />
<br />
<br />
<br />
     // display the result <br />
<br />
	 cout << endl; <br />
     cout << "Your grade for CMSC 101 is: " << grade << endl; <br />
     return (0); // terminate with success

Re: Help with code

Naveen21-Oct-08 16:08

Naveen

21-Oct-08 16:08

dtaylor01 wrote:
if (score >= 85);
else if (score >= 75);
else if (score >= 65);
else if (score >= 55);

remove the semi colon's at the end of if statement and else if statement...

nave

[OpenedFileFinder] [My Blog]

Re: Help with code

CPallini21-Oct-08 21:36

CPallini

21-Oct-08 21:36

In addition to Naveen reply:

dtaylor01 wrote:
End if

There's not an End if keyword in C/C++.

Bottom line: Good C/C++ tutorial required.
Smile | :)

Re: Help with code

Iain Clarke, Warrior Programmer21-Oct-08 21:59

Iain Clarke, Warrior Programmer

21-Oct-08 21:59

You've been given answers to the problems I can see (and I didn't catch the ; first).

But you didn't need us to tell you about them - any compiler would have choked on your code, and treated you to a barrage of bad language. Those errors are your (sarcastic picky) friend. Apart from anything else, people who come here to help expect you to have done some of the heavy lifting already.

1/ "else"? whatdaya mean "else". There should be an if first!
would have given you a hint towards the ; Not an easy hint one though.

I personally dislike using the style for very trivial ifs, but many people insist on putting squiggly brackets round every if case, which will make it easier for you while starting. It also makes it harder to make an error when you add more than one line to and if case.

eg:

if (score > 85)
{
    grade = 'A';
}
else if (score >= 75)
{

2/ "end"? Never heard of it.
Easy hint.

Linker options

freeheap21-Oct-08 9:08

freeheap

21-Oct-08 9:08

Hi.I'm trying to compile a project with Visual Studio 2008, but I need to modify my linker settings to include wsock32.lib. How can I do this?

Re: Linker options

Perspx21-Oct-08 9:51

Perspx

21-Oct-08 9:51

Go to Project > Properties in the main window, then in the dialog that pops up, Configuration Properties > Linker > Input. Type the library name into the Additional Dependencies box.

Regards,
--Perspx

"I've got my kids brainwashed: You don't use Google, and you don't use an iPod." - Steve Ballmer

"Some people have told me they don't think a fat penguin really embodies the grace of Linux, which just tells me they have never seen an angry penguin charging at them in excess of 100mph." - Linus Torvalds

Need help with mutex

auralius manurung21-Oct-08 6:42

21-Oct-08 6:42

I have this class:

class CPROXY
{
public:
			
	CPROXY(void);
	~CPROXY(void);
	int CreateConnector();
	int CreateAcceptor(int nPort);
	:
	:
        :

private:

	ACE_SOCK_Acceptor	client_acceptor;
	ACE_SOCK_Connector	server_connector;

	std::list <spair*>	queue;
}

Now the implementation is like this:

int CPROXY::ServerThreadRunner()
{
        :
	DWORD thid;
	HANDLE hServerThread = CreateThread(NULL, 0, ServerThread, this, 0, &thid);
	:
        :
}


DWORD WINAPI CPROXY::ServerThread(LPVOID param)
{
	CPROXY *newobj = (CPROXY *)param;

	newobj->CreateConnector();

	return 0;
}

int CPROXY::CreateConnector()
{
	EnterCriticalSection(&guard);
	SPAIR *sPair = queue.front();
	queue.pop_front();
	LeaveCriticalSection(&guard);

	SetEvent(wait_server);
	:
	:
        :

Take a look at queue. Queue is declared as a list of SPAIR. Do you think it is necessary for me to guard it with critical section every time is accessed by a thread?

I mean, before i run the thread i did put it into a newobj, so meaning that every newobj has its own member so no need for me to put critical section to guard it, right?

PLEASE, correct me if I'm wrong! i need to optimize this code.

Mark Salsbery21-Oct-08 6:56

21-Oct-08 6:56

auralius wrote:
before i run the thread i did put it into a newobj, so meaning that every newobj has its own member

I'm not sure what you mean by that.

Your code doesn't show how many CPROXY objects are created.

Just because you do this:

CPROXY *newobj = (CPROXY *)param;

doesn't mean there's a new CPROXY object - it's just a pointer to an object
that is passed to the thread.

If every thread has its own CPROXY object, then no, you don't need synchronization.

If every thread is using the same CPROXY object, and there's any chance more than
one thread can access this object at the same time, then yes you need synchronization.

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

auralius manurung21-Oct-08 10:52

21-Oct-08 10:52

Thank for your reply.
I mean there is a main function that will call int ServerThreadRunner(). Meaning that for every thread will be handled by new CPROXY newobj pointer.

So, if it is only pointer pointing the same location, does it mean that i need to put synchronization for every data member that accessed by the thread function?

How about this:

std::list <spair> queue;
vs
std::list <spair*> queue;

which one needs synchronization, and which one doesn't need?

What came to my mind is: there is no need for synchronization unless i put the queue as a static variable. am i right?

static std::list <spair*> queue;

sorry if my question is not really good. i hope you understand. i can't just solve that problem by trial & error because both of them work. I need strong concept.

Mark Salsbery21-Oct-08 11:06

21-Oct-08 11:06

auralius wrote:
eaning that for every thread will be handled by new CPROXY newobj pointer.

Different pointers to CPROXY objects is not the same as different CPROXY objects.
All the threads will have their own pointers but they could all point to the same
object, in which case you'd need synchronization.
If there's a separate CPROXY object for every thread, then no synchronization is necessary.

auralius wrote:
there is a main function that will call int ServerThreadRunner()

Can you show how you do that?

auralius wrote:
What came to my mind is: there is no need for synchronization unless i put the queue as a static variable. am i right?

No. It all comes down to actual object instances. Multiple threads can access
a single object instance no matter how it's stored. If multiple threads can
change the same object, then that object should be protected with synchronization.

You haven't shown relevant code so it's hard to tell if you need it there or not.

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

auralius manurung21-Oct-08 17:02

Re: Need help with mutex [modified]

21-Oct-08 17:02

class CPROXY
{
public:
			
	CPROXY(void);
	~CPROXY(void);

	int Run(int nPort);

	static DWORD WINAPI MotherThread(LPVOID param);
	static DWORD WINAPI DaughterThread(LPVOID param);
	int MotherThreadWorker();
	int DaughterThreadWorker();

	int GetAddressAndPort(char * cStr, char *cAddress, int * nPort);


private:

	ACE_SOCK_Acceptor	client_acceptor;
	ACE_SOCK_Connector	server_connector;

	CRITICAL_SECTION	guard;
	HANDLE			wait;

	bool				isMotherThreadRunning;
	bool				isDaughterThreadRunning;

	static std::list<ACE_SOCK_Stream> queue;
};

The implementation is like this:

CPROXY::CPROXY(void)
{
	InitializeCriticalSection(&guard);
	wait = CreateEvent(NULL, FALSE, FALSE, NULL);
}

CPROXY::~CPROXY(void)
{
}

std::list<ACE_SOCK_Stream> CPROXY::queue; 

int CPROXY::Run(int nPort)
{
	DWORD thid;
	HANDLE hMotherThread = CreateThread(NULL, 0, MotherThread, this, 0, &thid);
	if (!hMotherThread)
		return -1;

	ACE_SOCK_Stream client_stream;
	ACE_INET_Addr addr;
	addr.set(nPort, addr.get_ip_address());

	int e = client_acceptor.open(addr);
	if (e == INVALID_SOCKET)
		return -1;

	while(true)
	{
		int e = client_acceptor.accept(client_stream);
		if (e == INVALID_SOCKET)
			continue;

		//Store in a buffer.
		EnterCriticalSection(&guard);
		queue.push_back(client_stream);
		LeaveCriticalSection(&guard);
	}
	
	return 0;
}

DWORD WINAPI CPROXY::MotherThread(LPVOID param)
{
	CPROXY *newobj = (CPROXY *)param;

	newobj->MotherThreadWorker();

	return 0;
}

int CPROXY::MotherThreadWorker()
{
	isMotherThreadRunning = true;

	while (isMotherThreadRunning)
	{
		EnterCriticalSection(&guard);
		bool isEmpty = queue.empty();
		LeaveCriticalSection(&guard);

		if (!isEmpty){
			DWORD thid;
			HANDLE hDaughterThread = CreateThread(NULL, 0, DaughterThread, this, 0, &thid);
			if (!hDaughterThread)
				continue;

			printf("\nWAITING!\n");
			WaitForSingleObject(wait, INFINITE);
			printf("\nFINISHED!\n");
		}
	}
	return 0;
}

DWORD WINAPI CPROXY::DaughterThread(LPVOID param)
{
	CPROXY *newobj = (CPROXY *)param;

	newobj->DaughterThreadWorker();
        :
        :
	return 0;
}

int CPROXY::DaughterThreadWorker()
{
	char buf[BUFSIZE];
	char cServerAddress[256];
	int  nServerPort;

	EnterCriticalSection(&guard);
	ACE_SOCK_Stream client_stream = queue.front();
	queue.pop_front();
	LeaveCriticalSection(&guard);

	SetEvent(wait);
        :
        :
        :
	return 0;
}

Here is the main file:

int main(int argc, char *argv[])
{
CPROXY *MyProxy = new CPROXY;
MyProxy->Run(ACCEPTOR_PORT);

while(1){}

return 0;
}

I've modified the code, now i put the list queue as a static. So what do you think? How if I change it into non-static. Does it still need synchronization? I also change the way i declare it.
From:
static std::list<ACE_SOCK_Stream> *queue;
To
static std::list<ACE_SOCK_Stream> queue;

So it is no longer a dynamic allocation. I just wanna do something with reason. If i use synchronization, i must be able to state clearly why i need it.

thank you vey2 much for your help... Smile | :)

Mark Salsbery21-Oct-08 18:17

21-Oct-08 18:17

auralius wrote:
Does it still need synchronization?

Yes.

Based on the code shown (if I read it correctly) you always have
the possibility of two threads simultaneously accessing the one queue -
either the main thread and the MotherThread or the main thread and the
DaughterThread.

There's only one queue object because there's only one CPROXY object, so
it doesn't make any difference where/how the one object is allocated.

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

modified on Wednesday, October 22, 2008 12:59 AM

auralius manurung21-Oct-08 19:43

21-Oct-08 19:43

Thank you very much for your help... i think i need to learn more and more...

Smile | :)

Mark Salsbery21-Oct-08 20:06