Base class constructors are automatically called for you if they have no argument. If you want to call a superclass constructor with an argument, you must use the subclass’s constructor initialization list. Unlike Java, C++ supports multiple inheritance (for better or worse), so the base class must be referred to by name, rather than “super()”. … Read more
This is because of padding added to satisfy alignment constraints. Data structure alignment impacts both performance and correctness of programs: Mis-aligned access might be a hard error (often SIGBUS). Mis-aligned access might be a soft error. Either corrected in hardware, for a modest performance-degradation. Or corrected by emulation in software, for a severe performance-degradation. In … Read more
When you add the const keyword to a method the this pointer will essentially become a pointer to const object, and you cannot therefore change any member data. (Unless you use mutable, more on that later). The const keyword is part of the functions signature which means that you can implement two similar methods, one … Read more
Preliminaries On modern computers, only the lowest level memory structures (the registers) can move data around in single clock cycles. However, registers are very expensive and most computer cores have less than a few dozen registers. At the other end of the memory spectrum (DRAM), the memory is very cheap (i.e. literally millions of times … Read more
In 2008 I provided a C++98 implementation of the Singleton design pattern that is lazy-evaluated, guaranteed-destruction, not-technically-thread-safe: Can any one provide me a sample of Singleton in c++? Here is an updated C++11 implementation of the Singleton design pattern that is lazy-evaluated, correctly-destroyed, and thread-safe. class S { public: static S& getInstance() { static S … Read more
“Slicing” is where you assign an object of a derived class to an instance of a base class, thereby losing part of the information – some of it is “sliced” away. For example, class A { int foo; }; class B : public A { int bar; }; So an object of type B has … Read more
string? wstring? std::string is a basic_string templated on a char, and std::wstring on a wchar_t. char vs. wchar_t char is supposed to hold a character, usually an 8-bit character. wchar_t is supposed to hold a wide character, and then, things get tricky: On Linux, a wchar_t is 4 bytes, while on Windows, it’s 2 bytes. … Read more
To expand on the answer by bradtgmurray, you may want to make one exception to the pure virtual method list of your interface by adding a virtual destructor. This allows you to pass pointer ownership to another party without exposing the concrete derived class. The destructor doesn’t have to do anything, because the interface doesn’t … Read more
vector1.insert( vector1.end(), vector2.begin(), vector2.end() );
The do … while and if … else are there to make it so that a semicolon after your macro always means the same thing. Let’s say you had something like your second macro. #define BAR(X) f(x); g(x) Now if you were to use BAR(X); in an if … else statement, where the bodies of … Read more