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In C++, a constructor of a class/struct can have an initializer list within the definition but prior to the constructor body. It is important to note that when you use an initialization list, the values are not assigned to the variable. They are initialized. In the below example, 0 is initialized into re and im. Example:
The most vexing parse is a counterintuitive form of syntactic ambiguity resolution in the C++ programming language. In certain situations, the C++ grammar cannot distinguish between the creation of an object parameter and specification of a function's type.
The technique was formalized in 1989 as "F-bounded quantification."[2] The name "CRTP" was independently coined by Jim Coplien in 1995, [3] who had observed it in some of the earliest C++ template code as well as in code examples that Timothy Budd created in his multiparadigm language Leda. [4]
Another example can be when dealing with structs. In the code snippet below, we have a struct student which contains some variables describing the information about a student. The function register_student leaks memory contents because it fails to fully initialize the members of struct student new_student.
For example, the compiler generated destructor will destroy each sub-object (base class or member) of the object. The compiler generated functions will be public, non-virtual [3] and the copy constructor and assignment operators will receive const& parameters (and not be of the alternative legal forms). [4]
It is also possible to tell most C and C++ compilers to "pack" the members of a structure to a certain level of alignment, e.g. "pack(2)" means align data members larger than a byte to a two-byte boundary so that any padding members are at most one byte long.
A struct can contain other data types so is used for mixed-data-type records. For example a bank customer struct might contains fields: name, address, telephone, balance. A struct occupies a contiguous block of memory, usually delimited (sized) by word-length boundaries.
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.