Copyright © 2016, 2017
Robert W. Hasker

Note 6: C++ Classes

Introduction to Classes

• [Give three differences between Java classes and C++ classes]
• Class std::string and #include <string>
  • string name = "Hello";
  • char first = name[0];
  • string as a built-in type: assignment, comparison
    
    • In particular, given string a = "this is a", b = "this is b"; then a < b is true
  • Full example:

                  string name = "John Xhu";
                  cout << name << endl;
                  string::size_type space_index = name.find(' ');
                  cout << "Index of space: " << space_index << endl;
                  if ( space_index == string::npos )
                     cout << "Not found" << endl;
                  cout << "Initials: " << name[0] << name[space_index + 1] << endl;
    

    • Better: auto space_index = name.find(' ');
  • std::string documentation:
    • see C++ Reference and the string reference (especially basic_string)
    • Operations: .size, .length, .empty, .clear, +, +=, .find
    • Example: program to read list of names, print first names
      • Check: need to #include <string>?
• Todo list with up to 100 items
  • constexpr for max size
  • constructor: list with no items
    • guaranteed to be run
    • first version: first item on list as argument
    • initializer: : size{1}
  • Operations: size, add (to end), nth, remove by position, remove by name
    • Precondition on add: must have space left
      • Consequences of violating the precondition
    • improvement over Java: can define your own operator[]:

             string operator[](int ix) { .... }
      

  • private, public, protected
• Array of todo lists: ToDo week[7];
  • Must have constructor with no arguments
  • Accessing: printing first item on each non-empty list
• Making the list resizable with arrays
• std::string as a resizable array
  • "C-style" strings -
    • will cover in more detail later
  • sentinel; null terminator; using '\0' and 0
  • operations to resize std::string
• (simple) linked list version of ToDo
  • Single links
    • (No destructors, copy constructors, etc.)
  • class StringNode
  • Group exercise: rewrite empty, full, add, next_item
  • Extend to support string operator[]
  • Revise operator[] to return string&
• Recall notion of memory map from SE 1011/1021 & Data Structures
  • Abstract view:

            +---------------+  
            |Type           |
            |               |
            |field: ___     |
            |field: ___     |              +----------------+
            |field:  O------+------------->|Type            |
            |               |              |                |
            +---------------+              |field: ____     |
                                           +----------------+
              
    

  • Also: activation record for methods and functions
  • [Draw memory map for linked list code]
  • Detailed memory map: memory = array with addresses & values

Differences from Java

• No need for public class - all classes are public

Review

• std::string
  • Avoid non-standard strings!
• c-style strings: null terminated; won't use until later
• classes, growable arrays, linked lists