The Standard C Library

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The Standard C Library
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Main Ideas

• Purpose
• Flexibility
• Efficiency
• Simple Uniform Interface

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Concepts

• A concept is a list of properties of a type.
• STL defines a hierarchy of concepts for
  containers, iterators, and element types.
• Concepts for element types include
• Concept B is a refinement of concept A if it
  imposes some additional requirements on A.
  (Similar to inheritance)

LessThan Comparable - types with operatorlt ,...
Equality Comparable - types with operator ,...
Assignable - types with operator and copy Ctor
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Main Components
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• Holds copies of elements.
• Assumes elements haveCopy Ctor operator
• The standard defines the interface.
• Two main classes
• Sequential containers list, vector,....
• Associative containersmap, set ...

Assignable - types with operator and copy Ctor
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Sequential Containers

• Maintain a linear sequence of objects

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Sequential Containers

• list - a linked list of objects
• Efficient insertion/deletion in front/end/middle
• vector - an extendable sequence of objects
• Efficient insertion/deletion at end
• Random access
• deque double-ended queue
• Efficient insertion/deletion at front/end
• Random access

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Containers Example - vectorltTgt

• Array of elements of type T
• Random Access
• Can grow on as needed basis

stdvectorltintgt v(2) v0 45 v1 32
v.push_back(60)
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Associative Containers

• Supports efficient retrieval of elements (values)
  based on keys.
• (Typical) Implementation
• red-black binary trees
• hash-table (SGI extension, not standard)

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Sorted Associative Containers

• Set
• A set of unique keys
• Map
• Associate a value to key (associative array)
• Unique value of each key
• Multiset
• Multimap
• Same, but allow multiple values

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Sorted Associative Containers Order

• Sorted Associative containers use operatorlt as
  default order
• We can control order by using our own comparison
  function
• To understand this issue, we need to use function
  object

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• Anything that can be called as if a function.
• For example
• Pointer to function
• A class that implements operator()
• Advantage of class
• Enable accumulating information in the function
  object

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Example

• templatelttypename Tgt
• class less
• public
• bool operator()(const T lhs, const T rhs)
• return lhs lt rhs
• lessltintgt cmp // declare an object
• if( cmp(1,2) )
• if( lessltintgt()(1,2) )

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Using Comparators

• templatelttypename T,
• typename Cmp lessltTgt gt
• class set
• setltintgt s1
• setltint,lessltintgt gt s2// same type

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Using Comparators

• templatelttypename T,
• typename Cmp lessltTgt gt
• class set
• setltint,MyComp gt s3
• MyComp cmp
• setltint,MyComp gt s4(cmp)

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• Iterators are allow to traverse sequences
• Main Methods
• operator
• operator, and operator
• Different types of iterators - to support read,
  write and random access
• Containers define their own iterator types
• Changing the container can invalidate the iterator

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(No Transcript)
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Iterator Types

• Output write only and can write only once
• Input read many times each item
• Forward supports both read and write
• Bi-directional support also decrement
• Random supports random access (just like C
  pointer)

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Iterators Containers

• Bidirectional iterators
• list, map, set
• Random access iterators
• vector
• Input/output/forward iterators
• iostreams

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Iterators and Containers

• class Container
• typedef iterator // iterator type of
  container
• iterator begin() // first element of
  container
• iterator end() // element after last of
  container

Container c Containeriterator i for( i
c.begin() i ! c.end() i) // do
something with i
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Iterators Map
Suppose we work with mapltstring,intgt
dictionary mapltstring,intgtiterator i i
dictionary.begin() What is the type of i ?
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Iterators Map

• Every STL container type Container defines
• Containervalue_type
• Type of elements stored in container
• This is the type returned by an iterator
• Containervalue_type
• Containeriterator operator()

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Iterators Map

• Ok, so what type of elements does a map return?
• mapltKeyType,ValueTypegt keeps pairs
• KeyType key key of entry
• ValueType value value of entry

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Pairs

• templatelt typename T1, typename T2gt
• struct pair
• typedef T1 first_type
• typedef T2 first_type
• T1 first
• T2 second
• pair( const T1 x, const T2 y )
• first(x), second(y)

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Map value_type

• templatelt typename Key, typename T,
• typename Cmp lessltKeygt gt
• class map
• public
• typedef pairltconst Key, Tgt value_type
• typedef Key key_type
• typedef T mapped_type
• typedef Cmp key_compare

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Using map iterator

• mapltstring,intgt dict
• mapltstring,intgtiterator i
• for( i dict.begin()
• i ! dict.end()
• i )
• cout ltlt i-gtfirst ltlt
• ltlt i-gtsecond ltlt \n

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• Good functionality, wrong interface
• For example, adaptors of basic containers
• Limited interface
• stackltT,Seqgt
• queueltT,Seqgt

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• Most STL algorithms works on sequences
• Sequences are passed as two iterators
• beginning element
• element one after last
• Algorithms depend on iterator type
• not on container type

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Copy

• templatelt typename In, typename Outgt
• Out copy(In first, In last, Out res)
• while (first ! last)
• res first
• return res

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Sort
template ltclass RandomAccessIterator,
class StrictWeakOrderinggt void
sort(RandomAccessIterator first,
RandomAccessIterator last,
StrictWeakOrdering comp)
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Cryptic error messages
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Cryptic error messages

• New solution in g, define before including a
• standard library header

define _GLIBCXX_CONCEPT_CHECKS
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Links to documentation

• SGI http//www.sgi.com/tech/stl/
• Dinkum http//www.dinkumware.com/refxcpp.html
• http//www.cplusplus.com/ref/

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Main Components
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Mutable
class String char _data mutable int
_len public String(const char data)
_data(data),_len(-1) void capitalie()
char p _data while (p) p toupper(p)
int length() const if (_len-1)
_lenstrlen(_data) return _len
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Inserters