Thread: Question on predefine macros

Hi , it's me again. I just came across predfine macros and was wondering how to use it so, I played around with one of the macros.

Code:

#include <iostream>
#define __TIMESTAMP__
using namespace std;


int main()
{
	cout << "Start time: \n" << __TIMESTAMP__ << endl;

	for(int x = 0; x < 5; x++)
		cout << x;

	cout << "End time is: \n" << __TIMESTAMP__ << endl;

 
	return 0;
}

The output of the time will always remain the same what ever code I put between them so, is there a way to update the time to see some effect, or am I doing something wrong with the code i.e. the time of the code executing is too fast to see anything?

Another question is, am I using the macros right? I didn't know how to output it in the first place but thought what the hell...try and cout the thing
-Kaminaga

1) The __TIMESTAMP__ macro is the time that the file was last modified. What a macro is is just a placeholder. When you compile your file, the compiler will begin by replacing every instance of __TIMESTAMP__ with the modification time (that time doesn't change; it is determined once at the start of compilation).
2) That macro is not part of C++ so if you use it be aware that you won't be able to compile it with all compilers.
3) To determine elapsed time, #include <ctime> and call clock() to store the time you start your calculation then call it again at the end of your calculation. The difference divided by built-in macro CLOCKS_PER_SEC is the elapsed time. Here's some code:

Code:

#include <ctime>
// ...
clock_t start, end;
double elapsed;

start = clock();
// do what you want to do (in living color)
end = clock();
elapsed = ((double) (end - start)) / CLOCKS_PER_SEC;
// ...

Do note, however, that the precision of this time is good but you might not see much elapsed time for such little code because it executes so rapidly. There are high resolutions timers available (depending on your compiler) but this method should suffice for your needs.

Both of you should carefully read the definition of __TIMESTAMP__.

You also need to figure out what a statement like this does:

#define name replacement

and then what a statement like this does:

#define name

[edit]
I realized my blunder. Pardon my mistatement.

Sorry if this post is long but I just wanted to make sure I can understand this better.

Lucky:
Thanks, I'm reading about it now in the MSDN library to understand more.

7stud:
I've read some of the stuff mentioned in the MSDN library, wasn't sure if I understand it properly but I'll give it ago.

1. I guess when you ask to read about the definition, I'm assuming this is the important part

"The date and time of the "last modification" of the current source file"

2. For #define name replacement:
The general form is
#define identifier token-string or #define macro-name character sequence.
So, if I made a

Code:

#define UP 1
#define Down 0

// and when I cout 

cout << UP << ' ' << UP << ' ' << DOWN << ' '<< DOWN << ' ';

//The output would be 1 1 0 0
/* So basically, the statements would cause the compiler to subsitute 1 and 0 everytime UP and DOWN is used */

3. For #define name
if I do something like #define BLAH_H. It will continue to be defined. I guess this one is pretty useful when I'm creating a seperate header file and also use #ifndef and #endif.
Again, correct me if I'm wrong

Orbitz
Sorry about that, I didn't check that one out thoroughly.
-Kaminaga

3. For #define name
if I do something like #define BLAH_H. It will continue to be defined. I guess this one is pretty useful when I'm creating a seperate header file and also use #ifndef and #endif.
Again, correct me if I'm wrong

That's not all that's going on. The replacement still occurs--even when you don't specify a set of replacement characters. If you don't specify a set of replacement characters, the name is replaced by nothing, which serves to remove the name from the file.