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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 following containers are defined in the current revision of the C++ standard: array, vector, list, forward_list, deque. Each of these containers implements different algorithms for data storage, which means that they have different speed guarantees for different operations: [1] array implements a compile-time non-resizable array.
The C++ standard library instead provides a dynamic array (collection) that can be extended or reduced in its std::vector template class. The C++ standard does not specify any relation between new / delete and the C memory allocation routines, but new and delete are typically implemented as wrappers around malloc and free. [6]
For example, to perform an element by element sum of two arrays, a and b to produce a third c, it is only necessary to write c = a + b In addition to support for vectorized arithmetic and relational operations, these languages also vectorize common mathematical functions such as sine.
When a class constructor does not explicitly call the constructor of one of its object-valued fields in its initializer list, the default constructor for the field's class is called. In the standard library, certain containers "fill in" values using the default constructor when the value is not given explicitly. E.g.
Copy constructors are the standard way of copying objects in C++, as opposed to cloning, and have C++-specific nuances. The first argument of such a constructor is a reference to an object of the same type as is being constructed (const or non-const), which might be followed by parameters of any type (all having default values).
The lazy initialization technique allows us to do this in just O(m) operations, rather than spending O(m+n) operations to first initialize all array cells. The technique is simply to allocate a table V storing the pairs ( k i , v i ) in some arbitrary order, and to write for each i in the cell T [ k i ] the position in V where key k i is stored ...
C++ also provides constructors to initialize an object, but they are often not as convenient as the initializer list. However, C++03 allows initializer-lists only on structs and classes that conform to the Plain Old Data (POD) definition; C++11 extends initializer-lists, so they can be used for all classes including standard containers like std ...