One of the corners of C++20 concepts is that there are certain situations in which you have to write requires requires. For instance, this example from [expr.prim.req]/3: A requires-expression can also be used in a requires-clause ([temp]) as a way of writing ad hoc constraints on template arguments such as the one below: template<typename T> … Read more
In several C++ examples I see a use of the type size_t where I would have used a simple int. What’s the difference, and why size_t should be better? 5 Answers 5
Specifically, if I have a series of if…else if statements, and I somehow know beforehand the relative probability that each statement will evaluate to true, how much difference in execution time does it make to sort them in order of probability? For example, should I prefer this: if (highly_likely) //do something else if (somewhat_likely) //do … Read more
With the new standard, there are new ways of doing things, and many are nicer than the old ways, but the old way is still fine. It’s also clear that the new standard doesn’t officially deprecate very much, for backward compatibility reasons. So the question that remains is: What old ways of coding are definitely … Read more
What are some good explanations on what argument dependent lookup is? Many people also call it Koenig Lookup as well. Preferably I’d like to know: Why is it a good thing? Why is it a bad thing? How does it work? 4 Answers 4
If I am allowed to do the following: template <typename T = int> class Foo{ }; Why am I not allowed to do the following in main? Foo me; But I must specify the following: Foo<int> me; C++11 introduced default template arguments and right now they are being elusive to my complete understanding. 6 Answers … Read more
Is there any code to find the maximum value of integer (accordingly to the compiler) in C/C++ like Integer.MaxValue function in java? 8 Answers 8
What are some really good reasons to ditch std::allocator in favor of a custom solution? Have you run across any situations where it was absolutely necessary for correctness, performance, scalability, etc? Any really clever examples? Custom allocators have always been a feature of the Standard Library that I haven’t had much need for. I was … Read more
What are the pros and cons of using Qt containers (QMap, QVector, etc.) over their STL equivalent? I can see one reason to prefer Qt: Qt containers can be passed along to other parts of Qt. For example, they can be used to populate a QVariant and then a QSettings (with some limitation though, only … Read more
Before you start yelling undefined behaviour, this is explicitly listed in N4659 (C++17) i = i++ + 1; // the value of i is incremented Yet in N3337 (C++11) i = i++ + 1; // the behavior is undefined What changed? From what I can gather, from [N4659 basic.exec] Except where noted, evaluations of operands … Read more
