How get bool's from std::vector<bool>

This is a discussion on How get bool's from std::vector<bool> within the C++ Programming forums, part of the General Programming Boards category; I don't know how many people know this but a vector of bools is not a container. (see this: http://www.gotw.ca/publications/mill09.htm ...

  1. #1
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    How get bool's from std::vector<bool>

    I don't know how many people know this but a vector of bools is not a container. (see this: http://www.gotw.ca/publications/mill09.htm for more info)

    I have a template'd function that works for everything except a vector of bools (again read the article to see why).

    Code:
    //My function is essentially like this
    template<class T>
    void f( T& t )
    {
        //Neither of these two statements work with bool
        typename T::value_type* p1 = &t[0];
        typename T::value_type* p2 = &*t.begin();
    
        // ... do something with *p1 and *p2 ...
    }
    So my question is: what's the best way to get the data from a vector of bools? Is the only way to loop through it and do it one item at a time?

    I tried:

    #define STD_VECTOR_BOOL_NOT_SPECIAL

    but that didn't do anything (using g++ 3.4.5).

  2. #2
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    Is there a reason you need it to work with a vector<bool>?

    I don't believe you can get the data out as an array.

  3. #3
    Cat without Hat CornedBee's Avatar
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    You cannot get the data as an array, because the data is not there.
    All the buzzt!
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    Quote Originally Posted by CornedBee View Post
    You cannot get the data as an array, because the data is not there.
    Yeah, I'm gonna have to force it to be a vector of chars instead.

  5. #5
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    Have you considered using std::basic_string<bool> instead?
    Having the word "string" in the name is obviously confusing, but I believe it should provide functionality that's pretty similar to a vector.
    Scott Meyers seems to agree with my suggestion and included it on his Book Errata list for "Effective STL" http://aristeia.com/BookErrata/estl1...ta_frames.html (search for "cpj").

  6. #6
    Algorithm Dissector iMalc's Avatar
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    You're mostly okay with vector<bool> as long as you don't try and take the address of one of the items. Just get a copy of each bool from an iterator or by index, and set it by assigning to the iterator or the setting the bool by array index.
    If that's not an option, then you need to use a vector of chars instead.
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  7. #7
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    or a deque<bool>

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