How to avoid pressing Enter with getchar for reading a single character only

Question

In the next code    include  lt stdio h gt   int main void         int c       while   c getchar      EOF            putchar c      return 0      I have to press Enter to print all the letters I entered with getchar  but I don t want to do this  what I want to do is to press the letter and immediately see the the letter I introduced repeated without pressing Enter  For example  if I press the letter  a  I want to see an other  a  next to it  and so on   aabbccddeeff        But when I press  a  nothing happens  I can write other letters and the copy appears only when I press Enter   abcdef abcdef   How can I do this   I am using the command cc -o example example c under Ubuntu for compiling

User · Answer

I like Lucas answer  but I would like to elaborate it a bit  There is a built-in function in termios h named cfmakeraw   which man describes as   cfmakeraw   sets the terminal to something like the  raw  mode of the old Version 7 terminal driver  input is available character by character  echoing is disabled  and all special processing of terminal input and output characters is disabled          This basically does the same as what Lucas suggested and more  you can see the exact flags it sets in the man pages  termios 3    Use case  int c   0  static struct termios oldTermios  newTermios   tcgetattr STDIN FILENO   amp oldTermios   newTermios   oldTermios   cfmakeraw  amp newTermios    tcsetattr STDIN FILENO  TCSANOW   amp newTermios   c   getchar    tcsetattr STDIN FILENO  TCSANOW   amp oldTermios    switch  c        case 113     q         printf   n n            exit 0           break      case 105     i         printf  insert n            break      default          break

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By default  the C library buffers the output until it sees a return   To print out the results immediately  use fflush   while  c getchar      EOF              putchar c       fflush stdout

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On a linux system  you can modify terminal behaviour using the stty command   By default  the terminal will buffer all information until Enter is pressed  before even sending it to the C program   A quick  dirty  and not-particularly-portable example to change the behaviour from within the program itself    include lt stdio h gt   include lt stdlib h gt   int main void     int c       use system call to make terminal send all keystrokes directly to stdin      system    bin stty raw      while  c getchar                    type a period to break out of the loop  since CTRL-D won t work raw        putchar c            use system call to set terminal behaviour to more normal behaviour      system    bin stty cooked      return 0      Please note that this isn t really optimal  since it just sort of assumes that stty cooked is the behaviour you want when the program exits  rather than checking what the original terminal settings were   Also  since all special processing is skipped in raw mode  many key sequences  such as CTRL-C or CTRL-D  won t actually work as you expect them to without explicitly processing them in the program   You can man stty for more control over the terminal behaviour  depending exactly on what you want to achieve

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This depends on your OS  if you are in a UNIX like environment the ICANON flag is enabled by default  so input is buffered until the next   n  or EOF  By disabling the canonical mode you will get the characters immediately  This is also possible on other platforms  but there is no straight forward cross-platform solution     EDIT  I see you specified that you use Ubuntu  I just posted something similar yesterday  but be aware that this will disable many default behaviors of your terminal     include lt stdio h gt   include  lt termios h gt               termios  TCSANOW  ECHO  ICANON  include  lt unistd h gt        STDIN FILENO   int main void          int c         static struct termios oldt  newt         tcgetattr gets the parameters of the current terminal     STDIN FILENO will tell tcgetattr that it should write the settings     of stdin to oldt       tcgetattr  STDIN FILENO   amp oldt         now the settings will be copied       newt   oldt         ICANON normally takes care that one line at a time will be processed     that means it will return if it sees a   n  or an EOF or an EOL       newt c lflag  amp     ICANON                    Those new settings will be set to STDIN     TCSANOW tells tcsetattr to change attributes immediately         tcsetattr  STDIN FILENO  TCSANOW   amp newt          This is your part      I choose  e  to end input  Notice that EOF is also turned off     in the non-canonical mode       while  c getchar       e                 putchar c                           restore the old settings       tcsetattr  STDIN FILENO  TCSANOW   amp oldt         return 0      You will notice  that every character appears twice  This is because the input is immediately echoed back to the terminal and then your program puts it back with putchar   too  If you want to disassociate the input from the output  you also have to turn of the ECHO flag  You can do this by simply changing the appropriate line to   newt c lflag  amp     ICANON   ECHO

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This code worked for me  Attention   this is not part of the standard library  even if most compilers  I use GCC  supports it    include  lt stdio h gt   include  lt conio h gt  int main int argc  char const  argv          char a   getch        printf  You typed a char with an ASCII value of  d  printable as   c  n   a  a       return 0      This code detects the first key press

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How to avoid pressing Enter with getchar       First of all  terminal input is commonly either line or fully buffered  This means that the operation system stores the actual input from the terminal into a buffer  Usually  this buffer is flushed to the program when f e   n was signalized provided in stdin  This is f e  made by a press to Enter   getchar   is just at the end of the chain  It has no ability to actually influence the buffering process          How can I do this     Ditch getchar   in the first place  if you don  t want to use specific system calls to change the behavior of the terminal explicitly like well explained in the other answers   There is unfortunately no standard library function and with that no portable way to flush the buffer at single character input  However  there are implementation-based and non-portable solutions     In Windows MS-DOS  there are the getch   and getche   functions in the conio h header file  which do exactly the thing you want - read a single character without the need to wait for the newline to flush the buffer   The main difference between getch   and getche   is that getch   does not immediately output the actual input character in the console  while getche   does  The additional  e  stands for echo   Example    include  lt stdio h gt   include  lt conio h gt      int main  void         int c       while   c   getche       EOF                if  c      n                         break                     printf   n               return 0        In Linux  a way to obtain direct character processing and output is to use the cbreak   and echo   options and the getch   and refresh   routines in the ncurses-library   Note  that you need to initialize the so called standard screen with the initscr   and close the same with the endwin   routines   Example    include  lt stdio h gt   include  lt ncurses h gt      int main  void         int c       cbreak         echo         initscr         while   c   getch       ERR                if  c      n                         break                     printf   n            refresh               endwin         return 0        Note  You need to invoke the compiler with the -lncurses option  so that the linker can search and find the ncurses-library

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Can create a new function that checks for Enter   include  lt stdio h gt   char getChar         printf  quot Please enter a char  n quot         char c   getchar        if  c      n                 c   getchar               return c     int main int argc  char  argv          char ch      while   ch   getChar                          printf  quot Your char   c n quot   ch              return 0

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I O is an operating system function   In many cases  the operating system won t pass typed character to a program until ENTER is pressed   This allows the user to modify the input  such as backspacing and retyping  before sending it to the program   For most purposes  this works well  presents a consistent interface to the user  and relieves the program from having to deal with this   In some cases  it s desirable for a program to get characters from keys as they are pressed   The C library itself deals with files  and doesn t concern itself with how data gets into the input file   Therefore  there s no way in the language itself to get keys as they are pressed  instead  this is platform-specific   Since you haven t specified OS or compiler  we can t look it up for you   Also  the standard output is normally buffered for efficiency   This is done by the C libraries  and so there is a C solution  which is to fflush stdout   after each character written   After that  whether the characters are displayed immediately is up to the operating system  but all the OSes I m familiar with will display the output immediately  so that s not normally a problem

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You could include the  ncurses  library  and use getch   instead of getchar

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Since you are working on a Unix derivative  Ubuntu   here is one way to do it - not recommended  but it will work  as long as you can type commands accurately    echo  stty -g   stty -g    gt  restore-sanity stty cbreak   your program   Use interrupt to stop the program when you are bored with it   sh restore-sanity    The  echo  line saves the current terminal settings as a shell script that will restore them  The  stty  line turns off most of the special processing  so Control-D has no effect  for example  and sends characters to the program as soon as they are available   It means you cannot edit your typing any more  The  sh  line reinstates your original terminal settings    You can economize if  stty sane  restores your settings sufficiently accurately for your purposes   The format of  -g  is not portable across versions of  stty   so what is generated on Solaris 10 won t work on Linux  or vice versa   but the concept works everywhere   The  stty sane  option is not universally available  AFAIK  but is on Linux

User · Answer

yes you can do this on windows too  here s the code below  using the conio h library    include  lt iostream gt    basic input output  include  lt conio h gt     provides non standard getch   function using namespace std   int main         cout  lt  lt   Password         string pass    while true                   char ch   getch                      if ch    r       when a carriage return is found  enter  key              cout  lt  lt  endl  lt  lt   Your password is     lt  lt  pass  lt  lt endl                break                               pass  ch                            cout  lt  lt                        getch      return 0

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getchar   is a standard function that on many platforms requires you to press ENTER to get the input  because the platform buffers input until that key is pressed   Many compilers platforms support the non-standard getch   that does not care about ENTER  bypasses platform buffering  treats ENTER like just another key

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I ve had this problem question come up in an assignment that I m currently working on  It also depends on which input you are grabbing from  I am using   dev tty   to get input while the program is running  so that needs to be the filestream associated with the command   On the ubuntu machine I have to test target  it required more than just  system   stty -raw       or  system   stty -icanon       I had to add the --file flag  as well as path to the command  like so   system    bin stty --file  dev tty -icanon       Everything is copacetic now

[c] How to avoid pressing Enter with getchar() for reading a single character only?

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