Object Construction in C++
- Memory for the object is allocated from the stack or the heap
- Memory from the heap is allocated using the operator
new
- Constructor initializes the allocated memory
- Constructor does not allocate memory
Object Memory Allocation
- Memory for the entire object is allocated first, including memory for all fields
- For an empty class, the size is always 1 to ensure that the addresses of two different objects will be different
- Size of an object is the sum of the size of the fields, plus the padding
- Memory for fields is constructed first
- Must know the fields of a class to know how much memory to allocate
Object Constructor Order
- Constructors for all fields are called before the constructor for the object
- Constructors are called in the order they appear in the class definition
Member Initialization Lists
- Part of the constructor
- Often ignored until after it is needed
- The only way that we can control what constructor is called for the fields of the class
- Syntax is a little strange but necessary
Non-Static Member Initialization
- Introduced in C++11
- Some limits to what types can be initialized and with what expressions
- It does help that you won't forget to initialize
- It does hurt that you cannot have initialization based on constructor parameters
- It does hurt that it exposes implementation details
- Use when appropriate
Good Practice
- Don't wait for a problem to occur
- Use the member initialization list as much as possible
- Use non-static member initialization when appropriate