getch() where is it getting from? k&r p.136

This is a discussion on getch() where is it getting from? k&r p.136 within the C Programming forums, part of the General Programming Boards category; Greetings, int c, getch(void); while (isspace(c = getch())) ; getch() where is it getting a character from? I checked The ...

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    getch() where is it getting from? k&r p.136

    Greetings,

    int c, getch(void);
    while (isspace(c = getch()))
    ;

    getch() where is it getting a character from?
    I checked The GNU Operating System but no getch (plenty of getchar).


    Also where can I view a "C" programmers reference guide?

    Thanks...vmars316
    Win7x64, HotBasic, 'Beginning C programming', 'Arduino Uno R3'.
    "All things in moderation, except for love and forgiveness"... www.vmars316.com

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    getch() gets character from stdin, is that what you mean?

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    Quote Originally Posted by camel-man View Post
    getch() gets character from stdin, is that what you mean?
    Yes, that's it, Thanks...vm
    Win7x64, HotBasic, 'Beginning C programming', 'Arduino Uno R3'.
    "All things in moderation, except for love and forgiveness"... www.vmars316.com

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    There's a reason it isn't documented: it's only available on old Windows machines.

    Getchar() is the standard equivalent present in every C implementation. Note: You have to press enter to make getchar() work, and it leaves the newline character in the buffer.

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    True, it's not standard C, but it's not only valid on old Windows (or DOS) machines, i.e. it's not just a legacy from Turbo C. It also exists as part of the ncurses library, which is still in use in the *nix world. Since it's not standard, we can't say for sure what it reads from without seeing the definition. But my guess is that it's defined elsewhere in the book. I don't have my K&R book handy, but IIRC from other threads here, it's a function that they wrote along with an ungetch. It is used to buffer keyboard input, in case your program read too far and needs to "unread" or "put stuff back in stdin". The ungetch puts it back in a stack (implemented as an array) so you can safely retrieve it later, as though you never read too far and it was still in the standard input buffer. It's used, as part of their RPN calculator example program, and maybe elsewhere.

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    The getch() that matters on page 136 in section 6.3 of K&R 2nd Ed.[1] is the one that is shown on page 79 in section 4.3. So compiler extensions do not matter.

    By the way, that getch() calls getchar() which, as already mentioned earlier in the thread, gets its input from stdin (also known as standard input).

    Is it really dangerous to use the verb "gets" in that last sentence or is that only when I use the function gets()?

    [1] Kernighan, Brian W. and Dennis M. Ritchie, The C Programming Language, Second Edition, Murray Hill, New Jersey: AT&T Bell Laboratories, 1988.
    Last edited by pheininger; 03-08-2012 at 05:14 AM. Reason: Add the line about gets. Then added full reference.

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