How to see if a user inputed a string

This is a discussion on How to see if a user inputed a string within the C++ Programming forums, part of the General Programming Boards category; Hello everyone, I trying to make a game in C++ right now and I want to make it so when ...

  1. #1
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    How to see if a user inputed a string

    Hello everyone,

    I trying to make a game in C++ right now and I want to make it so when a user types in
    a String instead of a int the whole program won't go crazy.
    And I have no idea how to do that so if you know how please post.


    Thanks.
    ~herocks

  2. #2
    Registered User IdioticCreation's Avatar
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    You could read it into a string, then use a function to extract the number from the string. If there is no number in the string then tell the player they must enter a number. Look up std::stringstream.

    Good Luck.
    David

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    Ah, I was thinking of doing that, but I only thought of half of what I should have thought.
    Thanks, I'll try it now.

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    Ok, Now I needa know how to convert a string to a int...I tried using the atoi() function but all it got me was a 0...

  5. #5
    Registered User IdioticCreation's Avatar
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    You can use stringstream for that.

    something like this:
    Code:
    std::string str;
    int an_int;
    std::stringstream s;
    s<< str;
    s>> an_int;

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    Thanks, but I just got it to work.
    Atoi returned a 0 ( NULL ) because I typed in a letter so I just have to see if the int equals NULL
    and if it dose, tell the user that its invalided.

  7. #7
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    IMO, the easiest way to check if the user inputs a string instead of an int is to check the state of the stream when you read in. When the user inputs a string and you attempt to read in an int, it will go into a fail state. This example clears the fail state, empties the stream of the invalid input, and attempts to read in the int again:
    Code:
    int value = 0;
    while (!(std::cin >> value))
    {
        std::cin.clear();
        std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
        // Error message and prompt again here.
    }
    You have to #include <limits> and <ios> for numeric_limits and streamsize. You can expand that pretty easily to also "fail" if the user enters an integer followed by characters, like 123abc.

  8. #8
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    What about:
    Code:
    cin.ignore(cin.rdbuf()->in_avail() );
    vs.
    Code:
    cin.ignore(numeric_limits<streamsize>::max(), '\n');

  9. #9
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    In my experience both work (don't forget the '\n' on the first one), but I believe the standard actually uses the numeric_limits version as an example so I prefer that one. I haven't read enough about in_avail() to be completely confident of its accuracy.

  10. #10
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    Thanks.

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