{"id":5761,"date":"2019-08-22T16:17:08","date_gmt":"2019-08-22T16:17:08","guid":{"rendered":"https:\/\/www.modernescpp.com\/index.php\/further-myths-from-my-readers\/"},"modified":"2019-08-22T16:17:08","modified_gmt":"2019-08-22T16:17:08","slug":"further-myths-from-my-readers","status":"publish","type":"post","link":"https:\/\/www.modernescpp.com\/index.php\/further-myths-from-my-readers\/","title":{"rendered":"Myths of My Blog Readers"},"content":{"rendered":"

I was inquisitive about your C++ myths. In particular, my German readers were quite active. I got a few E-Mails and observed a vivid discussion on Heise Developer<\/a>.<\/p>\n

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\"dragon<\/p>\n

Let me first conclude the myths of the C++ core guidelines before I write about your myths. Here is the last myth.<\/p>\n

NR.7: Don\u2019t: Make all data members protected<\/code><\/a><\/h2>\n

Protected data makes your program complex and error-prone. If you put protected data into a base class, you can not reason about derived classes in isolation and, therefore, you break encapsulation. You always have to reason about the entire class hierarchy.<\/p>\n

This means you have to answer at least these three questions.<\/p>\n

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  1. Do I have to implement a constructor in a derived class to initialize the protected data?<\/li>\n
  2. What is the actual value of the protected data if I use them?<\/li>\n
  3. Who will be affected if I modify the protected data?<\/li>\n<\/ol>\n

    Answering these questions becomes more and more complicated the deeper your class hierarchy becomes.<\/p>\n

    If you think about it: protected data is a kind of global data in the scope of the class hierarchy. And you know, a mutable shared state is terrible. It makes, for example, testing and concurrency quite tricky.<\/p>\n

    Now, I switch to your myths. I write about them in the order I received them.<\/p>\n<\/p>\n

    In C++ written programs need more memory and CPU as in C written programs (Gunter K\u00f6nigsmann)<\/h2>\n

    First of all: thanks to Gunter K\u00f6nigsmann for the classical myth.<\/p>\n

    Arguing against this myth is tricky and, in general, impossible for the C++ standard library. This is why I make only a few observations at the end of this chapter. First of all, here are the hard facts. The “Technical Report on C++ Performance” helps me a lot.<\/p>\n

    Technical report on C++ performance<\/a><\/h3>\n

    The Working Group WG 21 published in the year 2006 the paper ISO\/IEC TR 18015<\/a>. The title sounds not very interesting, but that document is the ultimate source if you want to get the performance numbers of the C++ features. The document expresses its concerns directly to the point.  <\/p>\n