I don’t think you can get “atomic” operation but using the Filesystem Technical Specification that has now been accepted as part of the Standard Library (C++17) you can resize the file like this: #include <fstream> #include <sstream> #include <iostream> #include <experimental/filesystem> // compilers that support the TS // #include <filesystem> // C++17 compilers // for … Read more
Unfortunately, there isn’t a single uniform interface or pattern for erasing elements from STL containers. But three behaviors emerge: std::vector Pattern To erase elements that fulfill a certain condition from a std::vector, a common technique is the so called erase-remove idiom. If v is an instance of std::vector, and we want to erase elements with … Read more
The reason this fails is because when you specify foo<Movable>, the function you’re binding to is: void foo(Movable&&) // *must* be an rvalue { } However, the value passed by std::bind will not be an rvalue, but an lvalue (stored as a member somewhere in the resulting bind functor). That, is the generated functor is … Read more
The C++ standard library does not have one, but Boost.Range has boost::counting_range, which certainly qualifies. You could also use boost::irange, which is a bit more focused in scope. C++20’s range library will allow you to do this via view::iota(start, end).
I have thought about this question quite a bit over the past four years. I have come to the conclusion that most explanations about push_back vs. emplace_back miss the full picture. Last year, I gave a presentation at C++Now on Type Deduction in C++14. I start talking about push_back vs. emplace_back at 13:49, but there … Read more
Keep in mind one thing before you read further: My answer is coming from the point of view of writing portable code that can be used in applications made up of modules compiled under different compilers. This can include different versions or even different patch levels of the same compiler. How can I use stl-classes … Read more
Overview This is a very interesting question with several answers. The “correct” answer is something you must decide for your specific application. With months, you can choose to do either chronological computations or calendrical computations. A chronological computation deals with regular units of time points and time durations, such as hours, minutes and seconds. A … Read more
The only case where it is OK to add a definition into the std namespace is specialization of a template that already exists in the namespace and to explicitly instantiate a template. However, only if they depend on a user defined type. [namespace.std] (standard draft): The behavior of a C++ program is undefined if it … Read more
std::pair provides pre-written constructors and comparison operators. This also allows them to be stored in containers like std::map without you needing to write, for example, the copy constructor or strict weak ordering via operator < (such as required by std::map). If you don’t write them you can’t make a mistake (remember how strict weak ordering … Read more
It’s almost always a bad idea to use the fscanf() function as it can leave your file pointer in an unknown location on failure. I prefer to use fgets() to get each line in and then sscanf() that. You can then continue to examine the line read in as you see fit. Something like: #define … Read more