Structures and Unions

Lecture 1 - Slide 21 : 34

A struct aggregates fields of different types to a new composite type

A union is the poor man's - the C programmer's - way of specializing a struct in two or more directions

Struct basics
- Consequtive memory (maybe slighly more than needed), fields of different types
- Direct component selection str.field - dot notation
  - Also indirect component selection from a pointer to a struct: str_ptr->field
- Bit fields: Access to selected bits in a field of integer type
Union basics
- A structure where all fields occupy the same memory
- No way to inquire about the actual type of contents
- Can be (mis)used to discover details about the representation of data
Value semantics
- Copied when passed as parameters
- Copied when returned from function
- If value semantics is too costly, pointers to structs can be used

The C struct is an important starting point of the C++ abstraction mechanisms and OOP