non-buffering stdin reading

My test application is

#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>

int main(int argc, char *argv[], char *envp[]) {
  int fd[2];

  if(pipe(fd) < 0) { 
    printf("Can\'t create pipe\n");
    exit(-1); 
  }

  pid_t fpid = fork();
  if (fpid == 0) {
    close(0);
    close(fd[1]);
    char *s = (char *) malloc(sizeof(char));
    while(1) if (read(fd[0], s, 1)) printf("%i\n", *s);
  }
  close(fd[0]);
  char *c = (char *) malloc(sizeof(char));
  while (1) {
    if (read(0, c, 1) > 0) write(fd[1], c, 1);
  }
  return 0;
}

I want to see char-code after each entered char. But in fact *s is printed only after '\n' in the console. So seems like stdin (file with desc 0) is buffered. But the read function is buffer-less, isn't it? Where am I wrong.

UPD: I use linux.

So the solution is

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <termios.h>

int main(int argc, char *argv[], char *envp[]) {
  int fd[2];

  if(pipe(fd) < 0) { 
    printf("Can\'t create pipe\n");
    exit(-1); 
  }

  struct termios term, term_orig;

  if(tcgetattr(0, &term_orig)) {
    printf("tcgetattr failed\n");
    exit(-1); 
  }

  term = term_orig;

  term.c_lflag &= ~ICANON;
  term.c_lflag |= ECHO;
  term.c_cc[VMIN] = 0;
  term.c_cc[VTIME] = 0;

  if (tcsetattr(0, TCSANOW, &term)) {
    printf("tcsetattr failed\n");
    exit(-1);
  }

  pid_t fpid = fork();
  if (fpid == 0) {
    close(0);
    close(fd[1]);
    char *s = (char *) malloc(sizeof(char));
    while(1) if (read(fd[0], s, 1)) printf("%i\n", *s);
  }
  close(fd[0]);
  char *c = (char *) malloc(sizeof(char));
  while (1) {
    if (read(0, c, 1) > 0) write(fd[1], c, 1);
  }
  return 0;
} 

Answers


Unfortunately, the behavior you're looking for is not possible with standard ANSI C, and the default mode for UNIX terminal I/O is line-oriented, which means you will always need an inputted \n character to retrieve the input. You'll need to use terminal I/O facilities that let you program in non-canonical mode, so that each key-press triggers an event. On Linux/UNIX, you can look into the <termios.h> header, or the ncurses library.


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