Not all types can be moved more efficiently than copied, and for some types it may make sense to even explicitly disable both copying and moving. Consider std::array<int, BIGNUM> as an an example of the former kind of a type. The point with the emplace functions and piecewise_construct is that such a class can be … Read more
From the cplusplus.com page about the begin member function of unordered_map (link): Notice that an unordered_map object makes no guarantees on which specific element is considered its first element. So no, there is no guarantee the elements will be iterated over in the order they were inserted. FYI, you can iterate over an unordered_map more … Read more
1). Are there any other differences between the two? I find std::atoi() a horrible function: It returns zero on error. If you consider zero as a valid input, then you cannot tell whether there was an error during the conversion or the input was zero. That’s just bad. See for example How do I tell … Read more
Go to Toolbar -> Settings -> Compiler In the Selected compiler drop-down menu, make sure GNU GCC Compiler is selected Below that, select the compiler settings tab and then the compiler flags tab underneath In the list below, make sure the box for “Have g++ follow the C++11 ISO C++ language standard [-std=c++11]” is checked … Read more
http://www.justsoftwaresolutions.co.uk/cplusplus/rvalue_references_and_perfect_forwarding.html Why is this useful? Well, it means that a function template can pass its arguments through to another function whilst retaining the lvalue/rvalue nature of the function arguments by using std::forward. This is called “perfect forwarding”, avoids excessive copying, and avoids the template author having to write multiple overloads for lvalue and rvalue references.
The OpenMP 4.0 specification was finalised and published several days ago here. It still mandates that parallel loops should be in the canonical form (§2.6, p.51): for (init-expr; test-expr; incr-expr) structured-block The standard allows for containers that provide random-access iterators to be used in all of the expressions, e.g.: #pragma omp parallel for for (it … Read more
Let’s see what the different calls that you provided do: emplace_back(mystring): This is an in-place construction of the new element with whatever argument you provided. Since you provided an lvalue, that in-place construction in fact is a copy-construction, i.e. this is the same as calling push_back(mystring) push_back(std::move(mystring)): This calls the move-insertion, which in the case … Read more
H2CO3 is right, you can use a makefile with the CXXFLAGS set with -std=c++11 A makefile is a simple text file with instructions about how to compile your program. Create a new file named Makefile (with a capital M). To automatically compile your code just type the make command in a terminal. You may have … Read more
By definition, default initialization is the initialization that occurs when no other initialization is specified; the C++ language guarantees you that any object for which you do not provide an explicit initializer will be default initialized (C++11 §8.5/11). That includes objects of type std::array<T, N> and T[N]. Be aware that there are types for which … Read more
On July 15 ’17 P0329R4 was accepted into the c++20 standard: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0329r4.pdf This brings limited support for c99’s Designated Initializers. This limitation is described as follows by C.1.7[diff.decl].4, given: struct A { int x, y; }; struct B { struct A a; }; The following Designated Initializations, which are valid in C, are restricted in … Read more