Basic STL

1. Basic STL Joe Meehean

2. C-style Strings Problems • need a function to figure out its size • no way to know its capacity • is it safe to append to the string • functions divorced from object • and they have weird names • cannot do simple deep copy assignment or construction • 3 steps to make a copy

3. C-style Strings Solution • What if we wrote a class that encapsulated string functionality? • How should we store the data internally?

4. C-style Strings Solution • What if we wrote a class that encapsulated string functionality? • How should we store the data internally? public class LCString{ private: char *c_str_; size_t size; size_t capacity_; };

5. C-style Strings Solution • What if we wrote a class that encapsulated string functionality? • What kind of constructors should we provide?

6. C-style Strings Solution • What if we wrote a class that encapsulated string functionality? • What kind of constructors should we provide? // Default LCString(); // Copy LCString(constLCString& orig); // C-style string LCString(const char* c_str);

7. C-style Strings Solution • What if we wrote a class that encapsulated string functionality? • What kind of methods should we implement?

8. C-style Strings Solution • What if we wrote a class that encapsulated string functionality? • What kind of methods should we implement? size_t size(); bool empty(); bool equals(constLCString& rhs); boollessThan(constLCString& rhs); char& at(int index);

9. C++ string class • Standard Template Library (STL) • C++ library of functions and classes • includes a string class already • all the class and function names are in a namespace called std • namespace is a user-defined scope • How do we use STL’s string? • #include <string> • put std::infront of all STL class names • e.g., std::string theString;

10. C++ string class • How do we use STL’s string ++? • #include <string> • tell the compiler you want to implicitly use STL’s scope • using namespace std; • e.g., string theString; • STL best practices • you can include STL headers (#include <string>) in your .h files • you can use STL’s namespace in your .cpp files • you should never use STL’s namespace in your header files

11. C++ string class • string constructors • default • copy • c-style string • literal string (e.g., “hello”) • a character and the number of times to repeat it

12. C++ string class • string methods • sizing • empty • size, returns string::size_t • string::size_t • size_t specialized just for strings • unsigned integral • large enough to give size of largest possible string

13. C++ string class • string methods • Relational operators • ==, != • case sensitive • <, <=, >, >= • if two strings are different lengths & every character in the shorter string matches corresponding character of longer string,shorter string is less than longer string • if characters of different, strings sorted by first differing character • often uppercase characters come before lower (not guaranteed)

14. C++ string class #include <string> using namespace std; string a(“Hello world”); string b(“Hello”); if( b != a ){ cout << “String differ” << endl; } if( b < a ){ cout << b << endl; }

15. C++ string class • string methods • Assignment • strings provide deep copy assignment • Concatenation • uses the + or the += operator • if left hand operand is a string, right hand operand can be a literal

16. C++ string class #include <string> using namespace std; string a(“Hello world”); string b(“ Hello”); string c = a + b; // “Hello world Hello” string d = a + “!!!!”; // “Hello world!!!!” string e = “!!!!” + a; // ERROR a += b; // “Hello world Hello” a += “!!!!” // “Hello world Hello!!!!”

17. C++ string class • string methods • Accessing the characters of a string • uses the [] operator • returns an assignable reference to character (l-value) #include <string> using namespace std; string a(“Hello world”); cout << a[0]; // ‘H’ cout << a[1]; // ‘e’ a[0] = ‘J’; // “Jello World” a[10] = ‘s’; // “JelloWorls”

18. C++ string class • character methods (once you’ve got them) • in <cctype> header • full list on p.89 of your book • determine character category • returns 0 if false, positive number otherwise • isalpha(c): true if c is a letter • isdigit(c): true if c is a digit • isupper(c): true if c is uppercase letter • convert letter to upper or lower case • tolower(c) • toupper(c)

19. Questions?

20. Array problems • They have a fixed size • you cannot grow or shrink them • They do not have assignment or copying • Need to pass size with it

21. STL Vector • vector • container that stores items in a specific order • similar to an array, except • grows dynamically • has deep copy and assignment • vector is a class template • class templates are classes that can store many types • (more on this in CS241) • need to tell a template what type to store • syntax: Class<Type> name; • e.g., vector<int> v;

22. STL Vector • vector • container that stores items in a specific order • similar to an array, except • grows dynamically • has deep copy and assignment

23. STL Vector • How do we use a vector? • another of STL’s classes • #include <vector> • using namespace std; OR std::vector<int> v; • vector is a class template • class templates are classes that can store many types • (more on this in CS241) • need to tell a template what type to store • syntax: vector<Type> name; • e.g., vector<int> v;

24. STL Vector • vector constructors • Default constructor • Copy constructor • copies items from original

25. STL Vector • vector constructors • vector(int n) • creates a vector with n items • if vector stores built-ins, items initialized to 0 • if vector stores class instances, items initialized using default constructor (just like an array) • vector(int n, type t) • create a vector with n items • items made by copying t

26. STL Vector • vector operations • size() • returns number of items in vector • return type is vector<type>::size_type • e.g., vector<string>::size_type s = string_vector.size(); • size_type is an integral (mostly interchangeable withunsigned integers)

27. STL Vector • vector operations • push_back(Type t) • adds t to the back of the vector • grows the vector by 1 • pop_back() • removes item at the back of the vector • vector shrinks by 1

28. STL Vector • vector operations • [] operator • returns item at index • like string’s [], return value is assignable (l-value) • access must between 0 and vector::size() • does not grow vector

29. STL Vector vs Array • Arrays • do not grow or shrink • can access any index between 0 and array capacity • e.g., char str[15]; str[14] = ‘c’ ; \\ OK • Vectors • grow and shrinks dynamically • can access indices between 0 and dynamic size • e.g.,vector<char> v_str;v_str.push_back(‘c’);str[1] = ‘d’; \\ERROR

30. Questions?