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QList<double> memory model ?

  • Hello,
    I have read in the documentation that for all types smaller or equal than a pointer a QList stores the values directly and not with pointers.
    That means for a 32-bit compiler, doubles will be stored with pointer. Is this correct?

    If yes, how can I avoid it, because for doubles this an enormous overhead and makes no sense.
    (Besides standard C-math-vector-functions will not run.)

  • Moderators

    That's correct. QList is not the best container if you care about contiguous memory layout. QVector is far better for that.
    If you want a list anyway then either switch to 64bit (which we all should've done long ago IMHO) or don't use QList (maybe a std::list instead?).

  • Lifetime Qt Champion


    To add to Chris, here you can find a very good analysis of Qt's and their STL's counterparts containers.

  • Hi @Chris-Kawa
    That is a pity. 64 bit is no way for me. I have subclassed the QList to integrate some useful additional functions, therefore I must do the same for QVector. I must think about it, maybe there is a way to write this code only once with templates.
    I there really not trick to force the QList to use contiguous layout for doubles ?

  • Hi @SGaist,
    thank for the tip, I will read it tomorrow.

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