Check if input has been recieved

This is a discussion on Check if input has been recieved within the C Programming forums, part of the General Programming Boards category; Is there a way to check whether an input has been received in c? for example say If I need ...

  1. #1
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    Check if input has been recieved

    Is there a way to check whether an input has been received in c?

    for example say If I need to input a variable with scanf, then trigger a string to be printed with printf, then input another variable, then run the program. e.g:

    Enter username: (printf)
    gorgeous george (If input recieved...)
    Enter password: (...then print this)
    george123 (scanf again)

    is there any function to do this? cheers

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    There is no standard function for doing this. Both Linux and Windows have system specific functions that in one way or another can let you know "is there anything entered" or "if no input for X time, tell me that there was nothing there".

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  3. #3
    and the Hat of Guessing tabstop's Avatar
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    All the input functions will wait patiently while input is typed in.

    You should also investigate fgets, to get the whole line vs. until the first space.

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    Quote Originally Posted by matsp View Post
    There is no standard function for doing this. Both Linux and Windows have system specific functions that in one way or another can let you know "is there anything entered" or "if no input for X time, tell me that there was nothing there".

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    Mats
    Ok, thanks, how does one make use of these commands in the program? I'm currently doing the programming on ubuntu.

    All the input functions will wait patiently while input is typed in.

    You should also investigate fgets, to get the whole line vs. until the first space.
    Thanks, i'll have a look a fgets, I can most definitelty use something like that.

    Actually Once the input is entered and you hit return, doesn't the program just continue to the next line, so I could use printf.. scanf... printf... scanf, and once I've entered the second input, it would continue?

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    ncurses

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    I'll have to look into these things, but right now I'm hitting the sack. Thanks for the replies

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    If you want to do it natively in Linux, you will need to use:
    http://www.manpagez.com/man/3/tcgetattr/
    http://www.manpagez.com/man/3/tcsetattr/
    http://www.manpagez.com/man/4/termios/

    There is also a "how to read input without enter" in the FAQ which shows some of the usage of these functions.

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    Quote Originally Posted by matsp View Post
    If you want to do it natively in Linux, you will need to use:
    http://www.manpagez.com/man/3/tcgetattr/
    http://www.manpagez.com/man/3/tcsetattr/
    http://www.manpagez.com/man/4/termios/

    There is also a "how to read input without enter" in the FAQ which shows some of the usage of these functions.

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    Mats
    Thanks, however I don't think I will actually need any of these things yet after all, as I realised all I want to do was continue with the program once the input had been recieved, so I now have something like:

    Code:
    float a,b;
    
    printf("Enter first value:");
    scanf("%f", b);
    printf("Enter second value:");
    scanf("%f",a);
    and this works how I want it too, since you are only prompted for the second value once you enter the first and hit return. I was thinking I might have to use an if function to see whether the input has been recieved, and i it has, then print the next line to prompt for value 2, but I see it's not that complicated after all.

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    And for robustness it would be a good idea to check if input has been received after all the program should not have to wait indefinitely for input.

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    Quote Originally Posted by itCbitC View Post
    And for robustness it would be a good idea to check if input has been received after all the program should not have to wait indefinitely for input.
    Why not? Unless there is a problem with waiting indefinitely (e.g. some other operation needs to be performed within a certain time), I don't see the problem with waiting. Yes, there are situations that you don't want to wait forever, but in most cases it's just fine to wait.

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    Quote Originally Posted by matsp View Post
    Why not? Unless there is a problem with waiting indefinitely (e.g. some other operation needs to be performed within a certain time), I don't see the problem with waiting. Yes, there are situations that you don't want to wait forever, but in most cases it's just fine to wait.

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    yeh and it saves me learning a hell of alot of information on linux specific functions, when all I want to do is wait for the user to input a value, then continue.

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    Quote Originally Posted by matsp View Post
    Why not? Unless there is a problem with waiting indefinitely (e.g. some other operation needs to be performed within a certain time), I don't see the problem with waiting. Yes, there are situations that you don't want to wait forever, but in most cases it's just fine to wait.

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    Sure no harm waiting not like its a resource hog but why wait indefinitely. The only reason for coding something like this would be to provide a shell environment for other programs.

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    Quote Originally Posted by itCbitC View Post
    Sure no harm waiting not like its a resource hog but why wait indefinitely. The only reason for coding something like this would be to provide a shell environment for other programs.
    Because there is no reason to NOT wait indefinitely, and it is a much easier way to handle things. If you want a timeout, you need to set things up with a timeout of some sort, then check the result and deal with what happens if you get a timeout. What are you going to do if there is a timeout? Exit, I suppose?

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    Quote Originally Posted by matsp View Post
    Because there is no reason to NOT wait indefinitely, and it is a much easier way to handle things. If you want a timeout, you need to set things up with a timeout of some sort, then check the result and deal with what happens if you get a timeout. What are you going to do if there is a timeout? Exit, I suppose?

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    Just a suggestion and as the O/P is content with waiting so be it and of course it keeps things simple. Certainly the code gets complicated if the program needs to either exit after a certain time or supply a default value and continue instead of waiting indefinitely.

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