[SOLVED] C loop .. continuation?

szboardstretcher · 11-25-2014, 12:54 PM

I have this code:

Code:

#include <stdio.h>

#define FALSE 0
#define  TRUE 1

int main(int argc, char *argv[]){
    int quit = FALSE;    
    int i = 0;
    int c;
    
    while (quit == FALSE) {
        ++i;    
        printf("counter   : %d \n", i);
        printf("last char : %c \n", c);
        c = getchar();
    }
    
    return 0;
}

Which runs and sits there waiting for input. Everytime a character is entered and 'enter' is pressed, the counter increases. However - it waits for this input.

How do you go about writing a 'game loop' in C, where the loop continues to run, the counter increases, while simultaneously looking for an input?

smallpond · 11-25-2014, 01:01 PM

The best way is to write your program as event-driven. When an event such as keyboard input occurs, then the handler for that event runs. The code may be multi-threaded to do this but doesn't have to be. Here's a sample library that should work for C code.

http://nikhilm.github.io/uvbook/basics.html

szboardstretcher · 11-25-2014, 01:15 PM

That is what I am looking for. Thank you.

One of the primary problems I am running into with learning programming is my lack of vocabulary. If I knew the lingo, I could easily do a search for this kind of thing.

genss · 11-25-2014, 01:24 PM

something like

Code:

int flags = fcntl(0, F_GETFL);
fcntl(0, F_SETFL, flags | O_NONBLOCK);

psionl0 · 11-25-2014, 01:28 PM

You have written an endless loop. You will never break out of the loop unless quit is set to TRUE (presumably depending on what is returned by getchar()).

szboardstretcher · 11-25-2014, 01:42 PM

Quote:

Originally Posted by psionl0

You have written an endless loop. You will never break out of the loop unless quit is set to TRUE (presumably depending on what is returned by getchar()).

Yes, thank you. Do you have any reply to the actual question?

Code:

int flags = fcntl(0, F_GETFL); 
fcntl(0, F_SETFL, flags | O_NONBLOCK);

Thank you. Any explanation as to how this answers my question?

NevemTeve · 11-25-2014, 02:08 PM

Quess your question is: why do you have to press Enter to see anything. It's because of line-buffering. termios is your friend, example program: shkeys.c

genss · 11-25-2014, 02:15 PM

Quote:

Originally Posted by szboardstretcher

Code:

int flags = fcntl(0, F_GETFL); 
fcntl(0, F_SETFL, flags | O_NONBLOCK);

Thank you. Any explanation as to how this answers my question?

non-blocking io mode meaning read() without anything written to it will return -EAGAIN
iirc

file descriptor 0 is stdin

bdw, normally you would write games using SDL or GLFW
they bout have cross platform input support
GLFW even has 2 types of input functions, when checked (if pressed/released/etc) and a callback function (similar)

szboardstretcher · 11-25-2014, 02:17 PM

So far it seems that libuv is the accepted way of doing this - as explained above.

Also, ncurses allows easy non-blocking input control.

genss · 11-25-2014, 02:35 PM

and i just hacked something :/

Code:

#include <stdio.h>
#include <fcntl.h>

#define FALSE 0
#define  TRUE 1

int main(int argc, char *argv[]){
    int quit = FALSE;    
    int i = 0;
    char c;
    int err;
	
    fcntl(0, F_SETFL, fcntl(0, F_GETFL) | O_NONBLOCK);
	
    while (quit == FALSE) {
        ++i;
        err = read(0, &c, 1);
	if( err > 0 ) {
            printf("counter   : %d \n", i);
            printf("this char : %c \n", c);
	}
    }
    
    return 0;
}

maybe termios would be better

note that this most probably won't work on windows

edit:
note that UNICODE can be multibyte and that if the loop is slow there can be multiple chars buffered
so a bigger buffer and handle if bytes read ("err" in this case) is same as asked for

psionl0 · 11-25-2014, 07:59 PM

Quote:

Originally Posted by szboardstretcher

Yes, thank you. Do you have any reply to the actual question?

From the way your OP was worded, I didn't realize that you wanted a function that would not wait until a key was actually pressed before returning.

One way to achieve that would be with the kbhit() function but that is in conio which linux doesn't have. If your system has caca_conio libraries then caca_conio_kbhit() would be an equivalent. (#include <caca_conio.h>).

Another alternative is suggested here: http://www.flipcode.com/archives/_kbhit_for_Linux.shtml

mina86 · 11-26-2014, 07:46 AM

There were several answers here and the topic is marked as solved, but I don't know if proper solution has been communicated, so let me make it clear:
1. No, you don't want to set O_NONBLOCK.
2. Yes, what NevemTeve wrote is correct, you should listen to him.
3. Yes, what psionl0 wrote is correct, you should listen to him.
Hope this helps to clarify things and clear out confusion.

genss · 11-26-2014, 08:09 AM

Quote:

Originally Posted by mina86

There were several answers here and the topic is marked as solved, but I don't know if proper solution has been communicated, so let me make it clear:
1. No, you don't want to set O_NONBLOCK.
2. Yes, what NevemTeve wrote is correct, you should listen to him.
3. Yes, what psionl0 wrote is correct if you're running under DOS or Windows.
Hope this helps to clarify things and clear out confusion.

i did say termios would probably be better (dk the use case)

http://pubs.opengroup.org/onlinepubs...d/termios.html
and man termios explain it,
the code linked to is too complicated for a newbie

psionl0 · 11-26-2014, 09:15 AM

Quote:

Originally Posted by mina86

3. Yes, what psionl0 wrote is correct if you're running under DOS or Windows.

I haven't tested it yet but my linux system has caca_conio installed so my advice should also be applicable for linux.

mina86 · 11-26-2014, 10:55 AM

Quote:

Originally Posted by genss

i did say termios would probably be better (dk the use case)

I just wanted to make sure that it's communicated clearly. File descriptor being non-blocking has nothing to do with terminal input buffering, and pointing people to O_NONBLOCK when what they need is termios is unhelpful and creates even more confusion about this already confusing subject.

Quote:

Originally Posted by psionl0

I haven't tested it yet but my linux system has caca_conio installed so my advice should also be applicable for linux.

I've updated my post.