How can I use input without waiting user to give something (using C) ?

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Hello!!
I'm using C language and I want to use an input ,without waiting for user input or pushing enter.(in python I can do this)-I guess here too.
For example,I want to print "hello\n" in console inside a while-loop and when user gives an input I want to print the given input ,without stop printing message "hello".

What I have tried:

#include <stdio.h>
#include <stdlib.h>
#include <curses.h>

int main(void)
{
initscr();
noecho();
cbreak(); // don't interrupt for user input
timeout(500); // wait 500ms for key press
char c;
int a = 1;
while(a == 1)
{
  c = getch();
  printf("hello\n");
  printf("%c key pressed...\n",c);
}
  endwin();
  nocbreak();
}

but I got this error:

/tmp/ccNmVWH7.o: In function `main':
input_no_wait.c:(.text+0x9): undefined reference to `initscr'
input_no_wait.c:(.text+0xe): undefined reference to `noecho'
input_no_wait.c:(.text+0x13): undefined reference to `cbreak'
input_no_wait.c:(.text+0x1a): undefined reference to `stdscr'
input_no_wait.c:(.text+0x27): undefined reference to `wtimeout'
input_no_wait.c:(.text+0x2e): undefined reference to `stdscr'
input_no_wait.c:(.text+0x36): undefined reference to `wgetch'
input_no_wait.c:(.text+0x54): undefined reference to `endwin'
input_no_wait.c:(.text+0x59): undefined reference to `nocbreak'
collect2: error: ld returned 1 exit status

--------------------------------------------------------------
gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0

I want your help.

Thanks in advance!!!

Posted 4-Aug-20 23:02pm

Nick_is_asking

Updated 12-Apr-22 10:26am

v3

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CHill60 · Answer 1 · 2020-08-04T23:15:00

Solution 1

I would have the main process working on one thread and the "waiting for user input" on another. Have a look at Using Worker Threads[^] for more info (sorry it uses C++ but look for the principles)
Another - this one in C# but the principles remain the same A Concise Overview of Threads[^]
An external (to Codeproject) article on Threading in C is this one from Cornell University[^]

Posted 4-Aug-20 23:15pm

CHill60

Comments

Nick_is_asking 5-Aug-20 6:46am

Is there anything else,because I don't understand??

CHill60 5-Aug-20 7:56am

Well you could look at the curses (programming library) - Wikipedia[^]
At some stage I advise you to get your head around threading though

Nick_is_asking 5-Aug-20 8:18am

I tried this one code:

#include <stdio.h>
#include <stdlib.h>
#include <curses.h>

int main(void)
{
initscr();
noecho();
cbreak(); // don't interrupt for user input
timeout(500); // wait 500ms for key press

int c = getch();
printf("%c\n",c);
endwin();
nocbreak();
return 0;
}

but I got this error:

/tmp/ccNmVWH7.o: In function `main':
input_no_wait.c:(.text+0x9): undefined reference to `initscr'
input_no_wait.c:(.text+0xe): undefined reference to `noecho'
input_no_wait.c:(.text+0x13): undefined reference to `cbreak'
input_no_wait.c:(.text+0x1a): undefined reference to `stdscr'
input_no_wait.c:(.text+0x27): undefined reference to `wtimeout'
input_no_wait.c:(.text+0x2e): undefined reference to `stdscr'
input_no_wait.c:(.text+0x36): undefined reference to `wgetch'
input_no_wait.c:(.text+0x54): undefined reference to `endwin'
input_no_wait.c:(.text+0x59): undefined reference to `nocbreak'
collect2: error: ld returned 1 exit status

CHill60 5-Aug-20 12:22pm

Looks like the flags you have set on your Link options are incorrect. You'd have to share details of how you are compiling/linking. Might be best to put that in a separate question as it's not really related to your original question here. Make sure you include details of the IDE or Linker you are using as well as the options that you are using

Nick_is_asking 5-Aug-20 12:52pm

I compile like this: gcc name.c name and run like this ./name
I just want to get an input without waiting for user input and without pushing [ENTER] button.

CHill60 6-Aug-20 4:22am

There must be a config or settings file or similar - or perhaps you need one.
Can I suggest that you raise a new question about this - post your code and the error details as you have in your comment. Also include how you compile/link your code - include the name of the compiler that you are using too.
Hopefully someone who is more knowledgeable about C compilers on Ubuntu will be able to offer better help

Member 15600099 · Answer 2 · 2022-04-12T10:26:00

Check this:

C++

/**
 Linux (POSIX) implementation of _kbhit().
 Morgan McGuire, morgan@cs.brown.edu
 how to get a character from stdin without waiting for user to put it in C? */
#include <stdio.h>
#include <termios.h>
#include <sys/ioctl.h>
#include <sys/types.h>


int kbhit() {
    static const int STDIN = 0;
    static int initialized = 0;

    if (! initialized) {
        // Use termios to turn off line buffering
        struct termios term;
        tcgetattr(STDIN, &term);
        term.c_lflag &= ~ICANON;
        tcsetattr(STDIN, TCSANOW, &term);
        setbuf(stdin, NULL);
        initialized = 1;
    }

    int bytesWaiting;
    ioctl(STDIN, FIONREAD, &bytesWaiting);
    return bytesWaiting;
}

//////////////////////////////////////////////
//    Simple demo of _kbhit()

#include <unistd.h>

int  getch(void) {
    struct termios oldattr, newattr;
    int ch;
    tcgetattr( STDIN_FILENO, &oldattr );
    newattr = oldattr;
    newattr.c_lflag &= ~( ICANON | ECHO );
    tcsetattr( STDIN_FILENO, TCSANOW, &newattr );
    ch = getchar();
    tcsetattr( STDIN_FILENO, TCSANOW, &oldattr );
    return ch;
}

int main(int argc, char** argv) {
    printf("Press any key");
    while (! kbhit()) {
        printf(".");
        fflush(stdout);
        usleep(1000);
    }
    printf("\nDone. Las chars %d\n", getch());

    return 0;
}

Nick_is_asking · Answer 3 · 2020-08-07T04:56:00

I found a solution ,but I have to push a key I want twice instead of once.
Here is the code and I think the problem is to getch().
Can you help me to fix this problem(I want to push a button once and not twice).
Code:

C++

#include <stdio.h>
#include <termios.h>
#include <unistd.h>
#include <stdlib.h>
#include <time.h>
#include <sys/select.h>


int kbhit(void);
int getch(void);

int kbhit(void)
{
  struct timeval tv;
  fd_set read_fd;

  /* Do not wait at all, not even a microsecond */
  tv.tv_sec=0;
  tv.tv_usec=0;

  /* Must be done first to initialize read_fd */
  FD_ZERO(&read_fd);

  /* Makes select() ask if input is ready:
   * 0 is the file descriptor for stdin    */
  FD_SET(0,&read_fd);

  /* The first parameter is the number of the
   * largest file descriptor to check + 1. */
  if(select(1, &read_fd,NULL, /*No writes*/NULL, /*No exceptions*/&tv) == -1)
    return 0;  /* An error occured */

  /*  read_fd now holds a bit map of files that are
   * readable. We test the entry for the standard
   * input (file 0). */
  
if(FD_ISSET(0,&read_fd))
    /* Character pending on stdin */
    return 1;

  /* no characters were pending */
  return 0;
}




int  getch(void) {
    struct termios oldattr, newattr;
    int ch;
    tcgetattr( STDIN_FILENO, &oldattr );
    newattr = oldattr;
    newattr.c_lflag &= ~( ICANON | ECHO );
    tcsetattr( STDIN_FILENO, TCSANOW, &newattr );
    ch = getchar();
    tcsetattr( STDIN_FILENO, TCSANOW, &oldattr );
    return ch;
}



int main(){
        int a = 1;
   while(a == 1){
      if(kbhit() == 0){
         getch();
                 printf("%c is pressed\n",getch());
         
      }  
   }
  return 0;
}

For example, if I press 'a' and then again 'a' ,then I recieve -> a is pressed.
But I want to press 'a' only once to recieve -> a is pressed.
I need your help.

Thanks in advance...

How can I use input without waiting user to give something (using C) ?

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