read only 1 character in c++

Question

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How is std::iostream buffered?

This might sound ridiculous, but how can I read one char from cin in c++ (NOT until enter is pressed, just one character)? I've tried operator >>, get(), getchar(), but all of them reads a whole line.

All of the methods that you specify read one character from `std::cin`. That character isn't made available from the O/S, however, until ENTER is pressed. — Robᵩ, Apr 02 '12 at 18:19
What OS are you using? As Rob said, the OS holds the input until . To get a keyboard event when it happens, you need an OS-specific library. — Adam Shiemke, Apr 02 '12 at 18:22
@Robᵩ So what you say is that it is not possible to read only one char? All the other languages I know have a function for that. — Dave, Apr 02 '12 at 18:23
@Dave - It's not a language problem, it is system specific. I you run your program on a mainframe, the *terminal* will not send the input until you press Enter. C++ cannot do anything about that! — Bo Persson, Apr 02 '12 at 18:31

charley · Answer 1 · 2012-04-02T18:31:59.567

cin is buffered input. You want "unbuffered" input. It can be different on different platforms, unless you work directly with files.

Something like this might help:

http://www.cplusplus.com/forum/beginner/3329/

[EDIT], Remember that use of "buffered" v. "un-buffered" is a design decision, and both are legitimate. The "default" for "buffered-input" on cin makes a lot of sense, as the user will "backspace" to correct the input-line, and you don't want that "clutter" feeding your program. (And, in general, "buffered-input" like from files can be much more efficient.)

score 3 · Accepted Answer · answered Apr 02 '12 at 18:26

3

The _getche() function does what you want.

answered Apr 02 '12 at 18:26

Carey Gregory

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Yes, but he didn't ask for portability and he states in his comments above he's using Win7. Also, as Adam Shiemke and Rob pointed out, to get a keyboard event you're going to need an OS-specific function. – Carey Gregory Apr 02 '12 at 18:30

score 2 · Answer 3 · answered Apr 02 '12 at 18:31

While this is OS specific, in UNIX-like operating systems you can use the termios interface to disable input buffering on the terminal by putting it in non-canonical mode:

termios t;
tcgetattr(STDIN_FILENO, &t);
t.c_lflag &= ~ICANON;
tcsetattr(STDIN_FILENO, TCSANOW, &t);

See termios(3) for more details.

read only 1 character in c++

3 Answers3