C / C++ / MFC Discussion Boards

George221-Aug-03 15:46

21-Aug-03 15:46

Hello, everyone!

I think in C/C++ programming, you need to define a variable as
extern but there is no need to define a function as extern. The only
useful qualifier keyword used before a function is "static". And I
think you can use "#include .h" when you want to use other functions
defined in other files.

Am I correct?

regards,
George

Re: Need I define a function as "extern"?

Brad Sokol21-Aug-03 16:54

Brad Sokol

21-Aug-03 16:54

For free functions (C-ctyle functions), static means the function is not visible outside of the compilation unit (normally the .c or .cpp file).

The default is extern which means the function is visible - when an appropriate declaration is provided - outside of the compilation unit.

Brad

Re: Need I define a function as "extern"?

George221-Aug-03 23:28

George2

21-Aug-03 23:28

Thanks, Brad buddy!

Can you show me a case when "extern" keyword is a must? I think if we use
"#include .h" method, no extern functions are needed to use.

regards,
George

Re: Need I define a function as "extern"?

Brad Sokol22-Aug-03 1:52

Brad Sokol

22-Aug-03 1:52

extern is never required since it's the default i.e. if you want the function visible outside of the compilation unit specify extern or specify nothing. Both have the same meaning.

Brad

Re: Need I define a function as "extern"?

George222-Aug-03 2:10

George2

22-Aug-03 2:10

Thanks, Brad buddy!

George

Re: Need I define a function as "extern"?

Maxwell Chen21-Aug-03 20:09

Maxwell Chen

21-Aug-03 20:09

In addition to Brad's answer, I would like to show you some interesting example as demonstrated later in this message.

Anyway, I still recommend you getting a good C++ language book.

The example as:

[file main.cpp]
// #include "mod.h"

extern void Test();

extern void Test(); // Again, not my typo error. ;P

int iGlobalNumber;

void main()
{
	iGlobalNumber = 2;
	Test();
}

-----------------------
[file mod.cpp]
extern int iGlobalNumber;

void Test()
{
	iGlobalNumber = 1;
}
-----------------------
[There is no mod.H file]
-----------------------

BuggyMax

Re: Need I define a function as "extern"?

George221-Aug-03 23:24

George2

21-Aug-03 23:24

Thanks, BuggyMax buddy!

Why you use "extern void Test();" two times in main.cpp? It makes me puzzled.

regards,
George

Re: Need I define a function as "extern"?

Dangleberry22-Aug-03 4:09

Dangleberry

22-Aug-03 4:09

All the extern keyword does is apply external linkage. If there is a function declaration within a block of code (i.e. a function declaration within a function), it will have to use extern to force linkage outside the function scope.

Re: Need I define a function as "extern"?

George224-Aug-03 0:47

George2

24-Aug-03 0:47

Thanks, Dangleberry buddy!

But I have removed one of the two "extern void Test();" statements, and the
program still works OK. Can you explain to me why we need two "extern void Test();" statements here?

regards,
George

3D layer visualization

coda_x21-Aug-03 15:29

coda_x

21-Aug-03 15:29

how do i create a 3D visualization of a 2 layer structure? ie supppose i wan to have a 2nd layer (on top of a 1st layer) that follows the contours of the 1st layer(not necessarily flat)?

Read DLL source code

wow999921-Aug-03 15:24

wow9999

21-Aug-03 15:24

Hi all

how can i open a dll to read it's scource code?

Thanks

Re: Read DLL source code

Brad Sokol21-Aug-03 16:18

Brad Sokol

21-Aug-03 16:18

The short answer is you can't.

DLLs - and other types of Windows executable files like .exe, .scr, .cpl, ocx, and so on - contain machine code that has been compiled from higher level source languages.

With the exception of open source projects, the original source files - which are separate from the DLL - are almost never provided with an application.

Depending on what you're trying to learn, there may be other ways.

The web is an amazing place to find code that demonstrates how to do almost anything. CodeProject and MSDN are great places to start.

Using development tools that come with Visual Studio, the Platform SDK or sites on the web such as SysInternals, it is possible to view the DLL's external interface. From this, you may be able to learn a bit about what the DLL can do, but not how it does it.

Have a look at "OLE-COM Object Viewer" (Platform SDK) or "OLE Viewer" (Visual Studio 6.0. If the DLL implements COM objects, you can view the type library which show you the interfaces, methods, etc.

"Depends" which comes with Visual Studio lets you look at the functions and data exported by a DLL, as well as what other DLLs it depends on.

Process Explorer from SysInternals lets you see what DLLs a running program is using.

Hope that helps.

Re: Read DLL source code

Ryan Binns21-Aug-03 16:31

Ryan Binns

21-Aug-03 16:31

You can't get a DLLs source code from the DLL.

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

What project type to choose to run on all windows

Chris Ormerod21-Aug-03 14:23

Chris Ormerod

21-Aug-03 14:23

I have a need to create a setup wizard application that will have to do a lot of the same things as the initial VS.Net setup screen does, such as check system requirements, install required system files etc.

What type of project would I need to create in VS.Net 2003 to enable this to run directly off the CD-Rom on nearly all windows versions?

Chris.

Re: What project type to choose to run on all windows

David Crow22-Aug-03 3:19

David Crow

22-Aug-03 3:19

I've not ever used it but aren't programs created with VS.NET limited to run only on those machines having the .NET framework?

access JS vars on page in web browser control?

Scott H. Settlemier21-Aug-03 11:59

Scott H. Settlemier

21-Aug-03 11:59

I've got a web browser control.
It loads a page.
The page has some javascript.
In particular, one variable, an array is defined there.
I want it.
any ideas on how to get it?

Is this bad to do? (Networking question)

RobJones21-Aug-03 11:53

RobJones

21-Aug-03 11:53

Hello,
I am kind of worried about the following bit of code.. is it possible to have a socket block indefinitely? If so what could cause that?

if(sock == INVALID_SOCKET)
	return FALSE;

// Keep trying to send (if and only if our error is WSAEWOULDBLOCK.)
while(true)
{
	// Sending a structure..
	int nSend = send(sock,(char FAR*)&sSend, sizeof(sSend), 0);
	if(nSend == SOCKET_ERROR)
	{
		// If its WSAWOULDBLOCK keep looping.
		if(WSAGetLastError() != WSAEWOULDBLOCK)
			return FALSE;
	}
	else // NO ERROR
		break;
}

Whoever said nothing's impossible never tried slamming a revolving door!

Re: Is this bad to do? (Networking question)

Ryan Binns21-Aug-03 16:35

Ryan Binns

21-Aug-03 16:35

RobJones wrote:
is it possible to have a socket block indefinitely?

No. If there's no error, then it will send eventually. If there is an error, it will not block, but will return the error immediately.

And even if it takes ages to send the data, TCP includes timeouts, so it won't block forever - it will return a timeout error.

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

possible to provide VB app access to VC++ dll?

michael thomas21-Aug-03 10:32

michael thomas

21-Aug-03 10:32

Hi,

Thank you for stopping by.

I have a number of dlls written for VC++ 6 and I have been asked to make them available to a VB app (perhaps in the form of a .def file).

I would be very grateful to know what or how to go about doing this.

Any pointers would be much appreciated - the possibility of PAID work after so long is certainly a good incentive - I am sure you understand.

Please note that I am a VC++ programmer on version 6. I have yet to transition to .NET.

Thanks

Michael

Re: possible to provide VB app access to VC++ dll?

David Crow21-Aug-03 10:45

David Crow

21-Aug-03 10:45

Assuming the functions/classes in the C++ are exported, why not just add

Declare Function NameOfFunction Lib "NameOfLib" (ParameterList) As ReturnType

to the top of your VB modules?

Re: possible to provide VB app access to VC++ dll?

michael thomas21-Aug-03 11:02

michael thomas

21-Aug-03 11:02

Hi David,

Thank you for responding.

I have never produced a dll so I am completely ignorant of the terms, which I know is going to make this coding difficult. I guess I will have to go away and get familiar with how dlls are coded and generally fiddle around with them, since at this point I don't even know what 'exported' means.

At least you have given me a starting point and thanks for that.

Thanks

Michael

Re: possible to provide VB app access to VC++ dll?

vcplusplus21-Aug-03 11:27

vcplusplus

21-Aug-03 11:27

Check out the web site below

Calling DLL Functions from Visual Basic Applications
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vccore98/html/_core_calling_dll_functions_from_visual_basic_applications.asp

Re: possible to provide VB app access to VC++ dll?

michael thomas21-Aug-03 11:37

michael thomas

21-Aug-03 11:37

Excellent resource.

Thank you so much! I think this will do it.

Thanks again. You are a star!

Michael

Color of a pixel set by coordinates

Archigal21-Aug-03 10:24

Archigal

21-Aug-03 10:24

Hello

I have a HWND of a window and the coordinates of the pixel. How can I get a current color of this pixel?

The window is from another application.

Thank you in advance

Re: Color of a pixel set by coordinates

zeki yugnak21-Aug-03 12:39

zeki yugnak

21-Aug-03 12:39

hi..

if you know that coordinate's of pixel,you can use this function.

COLORREF GetPixel(
   int x,
   int y 
)

like this..

COLORREF color;
color=GetPixel(10,10);
int red=GetRValue(color);
int blue=GetBValue(color);
int green=GetGValue(color);

Good Work...

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