STL

1
STL

• CSE399
• March 19, 2007

2
Announcements

• Homework 5- Due Today
• No homework this week
• Work on your projects
• Speaking of projects
• Last week of class project demos
• 5-10 min
• Show me what your project does
• Answer some questions (What C features
  helped? etc)

3
MI Clarification

• class A .
• class B
• virtual void foo() .
• virtual void baz() .
• class C public A, public B
• virtual void bar() .
• virtual void foo() this-gtbar()

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Calling b-gtfoo()

• C c new C()
• / c 100 /
• B b c
• / b 120 /
• b-gtfoo()
• / this 120
• get foo from vtbl
• and call it /

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Calling c-gtbaz()

• C c new C()
• / c 100 /
• c-gtbaz()
• / C does not override baz(), baz() expects
  this to be a B. I.e.
• B temp c
• temp-gtbaz()
• /

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Suppose baz() calls foo()

• class A .
• class B
• virtual void foo() .
• virtual void baz() this -gtfoo()
• class C public A, public B
• virtual void bar() .
• virtual void foo() this-gtbar()
• ..
• C c new C() / c 100 /
• c-gtbaz()

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Standard Template Library

• Library of many useful containers / algorithms
• Templated- can handle many types
• In namespace std
• Google for C STL for documentation

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String class

• Unlike C, C has string type
• include ltstringgt
• string s hello / uses string(const char )
  /
• s
• string s2 wor
• s s2
• s ld
• cout ltlt s ltltendl
• const char c s.c_str() / get C string /

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Vectors

• C has vectorltTgt
• Similar in behavior (re-sizeable array) to Javas
• Overloaded operators gt syntax like array
• include ltvectorgt
• vectorltintgt v
• v.push_back(37) / Add to end /
• v.push_back(12)
• for (int i 0 i lt v.size() i)
• cout ltlt v ltlt i ltlt ltlt vi ltltendl

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Iterators

• Position in container
• vectorltintgtiterator it
• for ( it v.begin() it ! v.end() it )
• cout ltlt it ltlt endl
• Type inside container (vectorltintgtiterator)
• Many overloaded operators
• go to next element
• , ! compare positions
• reference to element in container at given
  position

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Algorithms

• STL also has some common algorithms
• include ltalgorithmgt
• sort(v.begin(), v.end()) / sort all of v /
• vectorltintgtiterator it
• it find(v.begin(), v.end(), 14)
• / it is an iterator with elements which 14 in
  v/

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Iterators Algorithms

• Notice sort find take iterators Why?
• Iterator (Container position)
• exactly the info sort/find need
• Iterators provide a very generic interface
• Avoids classes all inheriting from a superclass
• Avoiding multiple inheritance good

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Associative maps

• STL also has associative maps
• include ltmapgt
• mapltstring, intgt mp
• mpJan 1
• mpFeb 2
• mpMar 3
• .
• cout ltlt Mar is month ltlt mpMar ltlt endl
• Allows for maps from any (reasonable) type to any
  other type

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STL containee restrictions

• Types in STL containers must have an accessible
  (defaults OK where applicable)
• default constructor
• destructor
• assignment operator
• copy constructor
• Some things require inequality/equality operators

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C casts

• C style casts
• x (T) y
• C style casts
• 4 kinds of casts, each with different behavior

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Static cast

• x static_castltTgt(y)
• Most like C style casts
• double d 3.0
• int x static_castltdoublegt(d)
• Checks only static (compile time) info for safety
• int p static_castltint gt(d)
• invalid static_cast from type double to type
  int

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Const cast

• x const_castltTgt (y)
• Can only change constness
• const char y abc
• char x const_castltchar gt(y)
• Note does not actually make x mutable
• (i.e. x q may still result in a
  segfault)
• and volatility

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Dynamic Cast

• x dynamic_castltTgt(y)
• Checks for appropriate run time type when
  downcasting (Java like)
• Gives NULL (when casting pointers) or an
  exception (when casting references) if invalid
  cast
• class A
• class B public A
• A a1 new B()
• A a2 new A()
• B b1 dynamic_castltBgt(a1) / OK/
• B b2 dynamic_castltBgt(a2) / NULL /

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A side note

• class A
• class B public A
• A a1 new B()
• B b1 dynamic_castltBgt(a1)
• error canot dynamic_cast a1 (of type class
  A) to type class B (source type is not
  polymorphic
• Q What? A No virtual methods no vtbl

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Reinterpret Cast

• x reinterpret_castltTgt(y)
• Basically C style cast. Allows things like
• int p reinterpret_castltint gt(42)
• But screams Im not safe!

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Questions?

• Any questions?
• Also, requests for topics?
• 3 lectures remain
• Have covered major topics in C
• Want something re-covered? Something else
  discussed? E-mail me.