Condition question with VC++ 2008

This is a discussion on Condition question with VC++ 2008 within the C++ Programming forums, part of the General Programming Boards category; okay i have the following code the first condition produces a warning, and the second doesnt. I am curious as ...

  1. #1
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    Condition question with VC++ 2008

    okay i have the following code the first condition produces a warning, and the second doesnt. I am curious as to why it produces a warning in the first place.
    Code:
    static const int A = 1;
    static const int B = 2;
    
    int main()
    {
      if ( SomeFunc() == ( A || B ) ) // produces warning saying '==' : unsafe mix of type 'int' and type 'bool' in operation
         //do something
      if ( SomeFunc() == (int)( A || B ) ) //no warning due to cast, is there a problem with this?
        //do the same thing
    
    }
    Thank you for any insight.

  2. #2
    C++ Witch laserlight's Avatar
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    The warning is not required by the Standard, but is an attempt to be helpful. In this case I think it makes sense.

    The result of (A || B) is a bool. But what does SomeFunc() return? If it returns a bool, well and good. But it seems to return an int, and perhaps you did not intend to compare an int with a bool. This is what the warning is getting at.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    Yea, but how do i check if the function returned 2 integers?

  4. #4
    C++ Witch laserlight's Avatar
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    Yea, but how do i check if the function returned 2 integers?
    The function cannot return two integers, it can only return one integer. Did you write it yourself?
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    I said that the wrong way.
    1. Yes i do have class i made that allows a functions to return multiple values in a sense.
    2. I meant to ask how do i see which of the two integers the given function returned.

  6. #6
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    What you want is probably something like this:
    Code:
    int x = SomeFunc();
    if (x == 2 || x == 1) ...
    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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    Oh... so i can't do it by the return value inside the condition statement. Thank you.

  8. #8
    The larch
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    So, SomeFunc returns an integer and you want to check if the return value is either A or B.

    See, how the compiler got that warning right. This code indeed did something else than you intended. A || B produces true, which you cast to int in your attempt to suppress the warning, hence it becomes 1 and you end up checking if SomeFunc returns 1.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  9. #9
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    Quote Originally Posted by Raigne View Post
    Oh... so i can't do it by the return value inside the condition statement. Thank you.
    Well, if you want to be "complicated", you could do this:
    Code:
    int x;
    if ((x = SomeFunc()) == 1 || x == 2) ...
    But note the extra paranthesis that you need, if you get that wrong, it will still compile nicely, but the test will assign x with the value of (SomeFunc() == 1), which is either 0 or 1 depending on the return value from SomeFunc().

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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