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Resource management therefore needs to be tied to the lifespan of suitable objects in order to gain automatic allocation and reclamation. Resources are acquired during initialization, when there is no chance of them being used before they are available, and released with the destruction of the same objects, which is guaranteed to take place ...
For static-duration and automatic-duration variables, the size of the allocation must be compile-time constant (except for the case of variable-length automatic arrays [5]). If the required size is not known until run-time (for example, if data of arbitrary size is being read from the user or from a disk file), then using fixed-size data ...
The Standard C++ syntax for a non-placement new expression is [2]. new new-type-id ( optional-initializer-expression-list). The placement syntax adds an expression list immediately after the new keyword.
This feature is often used to manage resource allocation and deallocation, like opening and then automatically closing files or freeing up memory, called Resource Acquisition Is Initialization (RAII). Since C++11, C++ allows variables to be declared with the auto type specifier, [3] but this means that the variable's type is inferred, and does ...
[5] new and delete were, in fact, introduced in the first version of C++ (then called "C with Classes") to avoid the necessity of manual object initialization. [4] In contrast to the C routines, which allow growing or shrinking an allocated array with realloc, it is not possible to change the size of a memory buffer allocated by new[].
In manual memory allocation, this is also specified manually by the programmer; via functions such as free() in C, or the delete operator in C++ – this contrasts with automatic destruction of objects held in automatic variables, notably (non-static) local variables of functions, which are destroyed at the end of their scope in C and C++.
C++ enforces stricter typing rules (no implicit violations of the static type system [1]), and initialization requirements (compile-time enforcement that in-scope variables do not have initialization subverted) [7] than C, and so some valid C code is invalid in C++. A rationale for these is provided in Annex C.1 of the ISO C++ standard.
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: