C++ interactive command line prompt without waiting for a newline character - c++

Question

Is there a way to process command line input before seeing the newline character? I'm thinking of making a program that supports autocomplete (like the ones found in search engines or iOS keyboard).
To be more specific, my program will prompt for user input when started, and for each character input, I would like to output something BEFORE the newline character(or EOF) is input.
The following code snippet is what I have tried:
int main(){
char ch;
while ( (ch = cin.get()) != cin.eof() )
{
cout << ch << flush;
}
}
expected: for each character input, output that character.
actual: does not output anything UNTIL the program sees an eof.

Answer 1

In a Unix-like system, you can achieve this by changing the terminal to non-canonical input mode. Terminal supports canonical input which gathers the entire line for editing until the end of line character or Ctrl-D is pressed. As a result, the application often sees whole line on the read() system calls. On the other hand, non-canonical input does no line buffering; the input characters are made available to the program as soon as they are typed.
Here is a Linux C/C++ example of how to set -icanon flag (non-canonical) programmatically.
#include <iostream>
#include <termios.h>
#include <unistd.h>
int main() {
struct termios old_tio, new_tio;
tcgetattr(STDIN_FILENO, &old_tio);
new_tio = old_tio;
new_tio.c_lflag &= (~ICANON);
tcsetattr(STDIN_FILENO, TCSANOW, &new_tio);
char c;
while (fread(&c, 1, 1, stdin))
std::cout << c << std::endl;
return 0;
}