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In the C programming language, struct is the keyword used to define a composite, a.k.a. record, data type – a named set of values that occupy a block of memory. It allows for the different values to be accessed via a single identifier, often a pointer. A struct can contain other data types so is used for mixed-data-type records.
A class in C++ is a user-defined type or data structure declared with any of the keywords class, struct or union (the first two are collectively referred to as non-union classes) that has data and functions (also called member variables and member functions) as its members whose access is governed by the three access specifiers private, protected or public.
The automatically generated special member functions are: Default constructor if no other constructor is explicitly declared. Copy constructor if no move constructor and move assignment operator are explicitly declared. If a destructor is declared generation of a copy constructor is deprecated (C++11, proposal N3242 [2]).
In C++, default constructors take no parameters, instantiating the object members with their appropriate default values, "which is normally zero for numeral fields and empty string for string fields". [11] For example, a default constructor for a restaurant bill object written in C++ might set the tip to 15%:
The C syntactic form used in C99 is supported as an extension in the GCC and Clang C++ compilers. foo (& (struct X){4, 6}); // The object is allocated in the stack and its address can be passed to a function.
In 1989, C++ 2.0 was released, followed by the updated second edition of The C++ Programming Language in 1991. [32] New features in 2.0 included multiple inheritance, abstract classes, static member functions, const member functions, and protected members. In 1990, The Annotated C++ Reference Manual was published. This work became the basis for ...
Because default arguments' values are "filled in" at the call site rather than in the body of the function being called, virtual functions take their default argument values from the static type of the pointer or reference through which the call is made, rather than from the dynamic type of the object supplying the virtual function's body.
In theory, this function could affect a global variable, call other non-runtime constant functions, etc. C++11 introduced the keyword constexpr, which allows the user to guarantee that a function or object constructor is a compile-time constant. [11] The above example can be rewritten as follows: