C / C++ / MFC

28-Dec-06 6:12

My Dad just came across the following "interesting" bit of code while trying something out:

unsigned char fred[] = {1, 2, 3, 4};
unsigned char *p = fred;

printf("%d %d %d %d\n", fred[0], fred[1], fred[2], fred[3]);
// outputs: 1 2 3 4
printf("%d %d %d %d\n", *p++, *p++, *p++, *p++);
// outputs: 4 3 2 1

Looks like printf is being evaluated backwards, any idea as to the reasoning for this? Happens on the compiler he was using for the M16C and also on MSVC8.

I have no idea what I just said. But my intentions were sincere.

David Crow28-Dec-06 6:29

David Crow

28-Dec-06 6:29

Ed.Poore wrote:
...any idea as to the reasoning for this?

The result is undefined because the order of evaluation of function arguments are undefined. For more on this, search for sequence points.

"Approved Workmen Are Not Ashamed" - 2 Timothy 2:15

"Judge not by the eye but by the heart." - Native American Proverb

Ed.Poore28-Dec-06 6:57

28-Dec-06 6:57

Bizarre to say the least but at least we know it's there and can avoid it. Beer | [beer]

I have no idea what I just said. But my intentions were sincere.

Mark Salsbery28-Dec-06 7:10

Mark Salsbery

28-Dec-06 7:10

There's nothing bizarre about it. If the arguments are pushed on the stack from right to left
then it's behaving as implemented.

As David stated, this behavior is undefined. A C compiler is free to implement how function
calls are made in any way so relying on a specific behavior like this would be bad Smile | :)

Mark

Ed.Poore28-Dec-06 7:28

28-Dec-06 7:28

I agree with your points, it's just that he [Dad] thinks that it should work the way he says it should Big Grin | :-D

I have no idea what I just said. But my intentions were sincere.

Mark Salsbery28-Dec-06 7:41

Mark Salsbery

28-Dec-06 7:41

I agree. I'm ready for a compiler that works the way I say it should Laugh | :laugh:

Chris Meech28-Dec-06 11:40

Chris Meech

28-Dec-06 11:40

Like the PELC? (Plain English Language Compiler) Big Grin | :-D

Sorry, couldn't resist. Smile | :)

Chris Meech
I am Canadian. [heard in a local bar]
I agree with you that my argument is useless. [Red Stateler]
Hey, I am part of a special bread, we are called smart people [Captain See Sharp]
The zen of the soapbox is hard to attain...[Jörgen Sigvardsson]
I wish I could remember what it was like to only have a short term memory.[David Kentley]

Mark Salsbery28-Dec-06 11:50

Mark Salsbery

28-Dec-06 11:50

That's why I wear a robe and carry a staff when I code...

Ed.Poore28-Dec-06 12:12

28-Dec-06 12:12

Chris Meech wrote:
Sorry, couldn't resist.

You shouldn't have D'Oh! | :doh:

I have no idea what I just said. But my intentions were sincere.

Cristian Amarie28-Dec-06 22:47

Cristian Amarie

28-Dec-06 22:47

Ed.Poore wrote:
Looks like printf is being evaluated backwards

Have a look on printf implementation. It calls a function output (I think is in output.c file in folder crt).
From what I saw, printf evaluates from left to right the format string and uses the va_list argument as format specifier requires.

The arguments are probably stored in va_list from right to left, and your p points actually to the last argument. It's a __cdecl, after all.

(I am not sure - just thinking with loud voice).

Ed.Poore29-Dec-06 0:05

29-Dec-06 0:05

I'd take a look but it doesn't bother me, Dad can't understand why it does it that way but that's the way it does it so he has to put up with it. Poke tongue | ;-P

I have no idea what I just said. But my intentions were sincere.

pls help me

davvid28-Dec-06 6:09

davvid

28-Dec-06 6:09

how to print out the characters and integers mixed together randomly.

Johan Pretorius28-Dec-06 6:45

28-Dec-06 6:45

Could you please be a little more descriptive?

Artificial Intelligence is no match for Natural Stupidity

No one can understand the truth until he drinks of coffee's frothy goodness. ~Sheik Abd-al-Kadir

I can't always be wrong ... or can I?

davvid28-Dec-06 6:53

davvid

28-Dec-06 6:53

Hi ,
sorry anyway..

for example .. k 10 5 r 3 .. etc..
But I set 4 char and 10 int(frm 1-10) ..
thz in advance!

Hamid_RT28-Dec-06 17:19

Hamid_RT

28-Dec-06 17:19

Do you want to have string and integer together on output?

WhiteSky

CPallini28-Dec-06 7:22

CPallini

28-Dec-06 7:22

...rather vague... Confused | :confused:

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.

looping a function

dellthinker28-Dec-06 5:01

dellthinker

28-Dec-06 5:01

Hi all. I was just curious on how to keep a function going until i close the window manually. I know i'll need a loop of some sort however i dont know what i should do. I made a test function to see if i could do it.

<br />
#include <fstream><br />
using namespace std;<br />
int main (){<br />
	int loop;<br />
	for(loop=0;loop<=10;loop++)<br />
	{<br />
		printf("Test looping\n");<br />
	}<br />
	system("pause");<br />
	return 0;<br />
}<br />

Now anyone can clearly see that this function loops "Test looping" 10 times. But thats not my intention. Suppose i had a function that would check the time every 30 seconds, then print the time to a file. And it wouldnt stop until i forced it to stop. I hope im making sense, and that everyone understands. If im not being clear enough please let me know. Thanx in advance.

Kharfax28-Dec-06 5:07

Kharfax

28-Dec-06 5:07

I think you need to use a timer...

Gary R. Wheeler28-Dec-06 5:08

Gary R. Wheeler

28-Dec-06 5:08

dellthinker wrote:
system("pause");

A much easier way to do that:

printf("Press enter to continue...");
char buff[2];
fgets(buff,sizeof(buff),stdin);

Software Zen: delete this;

Fold With Us![^]

Johan Pretorius28-Dec-06 5:16

28-Dec-06 5:16

If it does not need to be time based then

while (!g_done)
{
//do what ever
}

and when your app receives the WM_CLOSE message set g_done to true.

Artificial Intelligence is no match for Natural Stupidity

No one can understand the truth until he drinks of coffee's frothy goodness. ~Sheik Abd-al-Kadir

I can't always be wrong ... or can I?

Kharfax28-Dec-06 5:22

Kharfax

28-Dec-06 5:22

mate, that will hang the app, to do that he will need to check for new messages in the queue and dispatch them.

Johan Pretorius28-Dec-06 5:28

28-Dec-06 5:28

i was assuming he is checking for messages. Smile | :)

Artificial Intelligence is no match for Natural Stupidity

No one can understand the truth until he drinks of coffee's frothy goodness. ~Sheik Abd-al-Kadir

I can't always be wrong ... or can I?

Johan Pretorius28-Dec-06 5:26

28-Dec-06 5:26

if it needs to be time based.

//in main function
static int timer_id = SetTimer(NULL,11,30000/*30sec* 1000millisecounds*/,NULL);

and your app should recive an WM_TIMER event every 30 secounds with wParam as the event number (11 in this case). There you can run your code.

When your app recives WM_CLOSE use

//this will stop your timer
KillTimer(timer_id);

Artificial Intelligence is no match for Natural Stupidity

No one can understand the truth until he drinks of coffee's frothy goodness. ~Sheik Abd-al-Kadir

I can't always be wrong ... or can I?

Johan Pretorius28-Dec-06 5:30