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

user_218808 0
Viewed 144544

In the next code:

#include <stdio.h>

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.

unbuffered getchar character input c
14 Answers

"How to avoid pressing Enter with getchar()?"

First of all, terminal input is commonly either line or fully buffered. This means that the operating system stores the actual input from the terminal in a buffer. Usually, this buffer is flushed to the program when e.g. \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 <stdio.h>
#include <conio.h>   

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 <stdio.h>
#include <ncurses.h>   

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.

user_121391790

This code worked for me. Attention : this is not part of the standard library, even if most compilers (I use GCC) supports it.

#include <stdio.h>
#include <conio.h>
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.

user_116862340

Can create a new function that checks for Enter:

#include <stdio.h>

char getChar()
{
    printf("Please enter a char:\n");

    char c = getchar();
    if (c == '\n')
    {
        c = getchar();
    }

    return c;
}

int main(int argc, char *argv[])
{
    char ch;
    while ((ch = getChar()) != '.')
    {
        printf("Your char: %c\n", ch);
    }

    return 0;
}
user_84766270

you can use _getch() instead of getch() from <conio.h>

user_187717230
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