Re: What is the difference between macro and simple code - C / C++ / MFC Discussion Boards

Cedric Moonen30-Oct-09 4:23

30-Oct-09 4:23

You should change your way of thinking: always initialize your variables. You should never have to test if a variable has been initialized or not.

Cédric Moonen
Software developer

Charting control [v2.0]
OpenGL game tutorial in C++

Re: variables

khomeyni31-Oct-09 3:30

khomeyni

31-Oct-09 3:30

in the name of god
thanks everybody.
i find my answer and thanks for everything. i promise you to don't question any other question that is irrelevant.

thanks.
valhamdolelah.

What is the difference between macro and simple code

deadlyabbas30-Oct-09 2:31

deadlyabbas

30-Oct-09 2:31

What is the difference between the following:

1. #Ifdef #else #endif and If else

Example:
#Ifdef 1
cout<<"Hello World"<<endl;
#else
cout<<"Have A Nice Day"<<endl;
#endif

and the code written as

if(1)
cout<<"Hello World"<<endl;
else
cout<<"Have A Nice Day"<<endl;

2.If we remove a macro from the code what impact we will have on the in respect to size of the code and the execution time and the size of exe.
Say we have a macro "RCAD"
The code looks like as
#if defined RCAD
// do some thing
#else
//do some thing
#endif

Now in our code the macro RCAD is always true so we remove the macro now
It will left only with
//do some thing

So what is the impact on our code and the size of it we doing the same thing.

Re: What is the difference between macro and simple code

enhzflep30-Oct-09 2:52

enhzflep

30-Oct-09 2:52

1. The difference is that the #define version only ends up in your executable if the #ifdef statement is satisfied. (The if is executed at compile time)
The if(1) version ends up in your executable, and the if(1) is executed every time program control passes it.

2. You'll have no impact on the exe size/speed. All it will do is remove the code from your source files (and has the potential to leave you with some 'fun' maintenance work later on)

Re: What is the difference between macro and simple code

deadlyabbas30-Oct-09 3:13

deadlyabbas

30-Oct-09 3:13

Can please tell me that what really internally happens when we use a macro.
I want to ask you that what is the difference in using macro and not using it
...................

Re: What is the difference between macro and simple code

David Crow30-Oct-09 3:27

David Crow

30-Oct-09 3:27

A preprocessor directive (some folks refer to it as macro but I feel that is incorrect) is removed by the preprocessor thus the compiler does not even see it. You can see this for yourself by using the /P or /E compiler switch.

"Old age is like a bank account. You withdraw later in life what you have deposited along the way." - Unknown

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

Re: What is the difference between macro and simple code

Maximilien30-Oct-09 3:33

Maximilien

30-Oct-09 3:33

The pre-processor (NOT the compiler) will parse the "#" and remove code that does not match the values...

for example :

#ifdef DEBUG
DoSomething();
#else 
DoSomethingElse();
#endif

if that code is pre-processed and the value DEBUG (see pre-processor definitions in the project settings) is defined, the preprocessor will generate the following code :

DoSomething();

if pre-processed in RELEASE, (DEBUG is not defined) :

DoSomethingElse();

and only that code will be compiled.

if you have

if (1)
{
DoSomething();
}
else
{
DoSomethingElse();
}

There is no macro, so the pre-processor will do nothing the that whole code will compiled by the compiler; as someone else wrote, in a simple compiler, generated assembly will be generated for both the if and the else; so there will be code bloat in the final executable, but in modern compilers, if code will never be called, it will be removed, and in that case, only the DoSomething(); will be effectively compiled into the executable.

This signature was proudly tested on animals.

Re: What is the difference between macro and simple code

Randor 30-Oct-09 2:59

Randor

30-Oct-09 2:59

Hi,

#Ifdef 1
cout<<"Hello World"<<endl;
#else
cout<<"Have A Nice Day"<<endl;
#endif

The compiler preprocessor will explicitly skip the code within the #else and no code will be generated because the previous condition was true.

if(1)
cout<<"Hello World"<<endl;
else
cout<<"Have A Nice Day"<<endl;

A non-optimizing compiler may generate code for both conditions including the impossible condition. An optimizing compiler will detect the second condition is unreachable and skip code generation.

Essentially you will probably get exactly the same result in both cases in a modern optimizing compiler in a Release build.

#if defined RCAD
// do some thing
#else
//do some thing
#endif

deadlyabbas wrote:
So what is the impact on our code and the size of it we doing the same thing.

The outcome will probably be exactly the same. By defining RCAD condition as true... the compiler ignores the other condition completely.

Best Wishes,
-David Delaune

Re: What is the difference between macro and simple code

CPallini30-Oct-09 2:59

CPallini

30-Oct-09 2:59

deadlyabbas wrote:
Example:
#Ifdef 1
cout<<"Hello World"<<endl;
#else
cout<<"have a="" nice="" day"<<endl;
#endif<="" blockquote="">
That's conditional compilation (compiler doesn't even 'see' the "Nice Day" statement, the preprocessor removes it).

deadlyabbas wrote:
if(1)
cout<<"Hello World"<<endl;
else
cout<<"have a="" nice="" day"<<endl;<="" blockquote="">
That's runtime evaluation of statements.

Hint: compile with /E flag to see the preprocessor in action.

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]

Read byte array from image

Game-point30-Oct-09 2:26

Game-point

30-Oct-09 2:26

Hello Sir,

How to read Byte array From image ?

in C# i can read perfect but in VC++ i dont know how to do it ?

Thanks !

Re: Read byte array from image

Randor 30-Oct-09 2:40

Randor

30-Oct-09 2:40

raju_Code wrote:
How to read Byte array From image ?

Do you mean from a GDI+ Image[^]?

Best Wishes,
-David Delaune

GDI+

__erfan__30-Oct-09 0:05

__erfan__

30-Oct-09 0:05

hi.
i want to write an image processing program and i don't need to preview the image so i decided to use win32 console application to avoid any unwanted delays. i want to use GDI+ classes but there is a runtime error.
my program :

#include "stdafx.h"
#include <windows.h>;
#include <gdiplus.h>;
using namespace Gdiplus;
int main()
{
	Bitmap *bmp;
	bmp = new Bitmap(L"my image path");
        unsigned int w = bmp->GetWidth(); // the error occurs in this line
	
        // my process
        //...
	return 0;
}

the error :
Unhandled exception at 0x00411761 in GdiPlusTest.exe: 0xC0000005: Access violation reading location 0x00000004.

any help? thanks.

Re: GDI+

CPallini30-Oct-09 0:18

CPallini

30-Oct-09 0:18

__erfan__ wrote:
i want to write an image processing program and i don't need to preview the image so i decided to use win32 console application to avoid any unwanted delays.

Hey, you're in the un-managed world here. Big Grin | :-D

Probably the bitmap object it is incorrectly built because you've not initialized, as required, the GDI+ library (MSDN [^]):

You must call GdiplusStartup before you create any GDI+ objects, and you must delete all of your GDI+ objects (or have them go out of scope) before you call GdiplusShutdown.

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: GDI+

Naveen30-Oct-09 0:19

Naveen

30-Oct-09 0:19

ops... A photo finish. and you won Smile | :)

nave

[My Articles] [My Blog]

Re: GDI+

Randor 30-Oct-09 0:22

Randor

30-Oct-09 0:22

I'm pretty sure he has borrowed some of Rajesh's monkeys. He only slept 4 hours last night. He is training them to play chess. Laugh | :laugh:

Best Wishes,
-David Delaune

Re: GDI+

Naveen30-Oct-09 0:29

Naveen

30-Oct-09 0:29

haaa...He took drug. see 'espresso'[^]

nave

[My Articles] [My Blog]

Re: GDI+

CPallini30-Oct-09 0:37

CPallini

30-Oct-09 0:37

Randor wrote:
I'm pretty sure he has borrowed some of Rajesh's monkeys

Randor wrote:
He is training them to play chess.

I actually was persuading one of them (the most appealing female of the group) to have some ...

(well I suppose it's not sister kid safe) Big Grin | :-D