Lesson of 22 July 2009

Example of the use of STL: the vector container

File stl.cc

  1/*
  2
  3  Example of use of STL (Standard Template Library)
  4  
  5  the vector container
  6
  7 */
  8
  9#include <iostream> // for I/O
 10#include <string>   // string support
 11#include <cmath>    // for sin, cos, ...
 12
 13#include <vector>     // the definition of STL vector container
 14#include <algorithm>  // the definition of the STL algorithm (sort, find,...)
 15
 16using namespace std ;
 17
 18int
 19main() {
 20  // define a as a vector of int
 21  vector<int> a ;
 22  
 23  a . push_back(12) ;
 24  a . push_back(4) ;
 25  
 26  cout << "a.front() = " << a.front() << '\n' ; // the first element
 27  cout << "a.back()  = " << a.back() << '\n' ; // the last element
 28  
 29  cout << "size of a = " << a . size() << '\n' ;
 30
 31  // define b as a vector of 10 float
 32  vector<float> b(10) ;
 33
 34  cout << "size of b = " << b . size() << '\n' ;
 35  
 36  b[2] = 30 ; // random access to the element of b
 37  b[5] = 12 ;
 38  b[9] = 1.34 ;
 39
 40  // loop on the vector C-style way
 41  for ( int i=0 ; i < b.size() ; ++i )
 42    cout << "b[" << i << "] = " << b[i] << '\n' ;
 43    //                               ^
 44    //                               |
 45    // access to the i-th element of vector b
 46
 47  // loop on the vector STL-style way
 48  for ( vector<float>::iterator i = b . begin() ;
 49        i != b . end() ;
 50        ++i ) // increment the iterator to "point" to the next object in 
 51              // the vector b (an instance of vector<int>)
 52    cout << *i << '\n' ;
 53    //                              ^
 54    //                              |
 55    // access to the element of vector b pointed by iterator i
 56
 57  // Algorithms
 58  
 59  cout << "do sort\n" ;
 60
 61  sort( b.begin(), b.end() ) ;
 62  //reverse( b.begin(), b.end() ) ;
 63  //sort( b.rbegin(), b.rend() ) ;
 64
 65  for ( vector<float>::iterator i = b . begin() ; i != b . end() ; ++i ) 
 66    cout << *i << '\n' ;
 67
 68  vector<float>::iterator i = max_element( b.begin(), b.end() ) ;
 69  cout << "maximum element = " << *i << '\n' ;
 70  
 71  b . clear() ; // cancel all the elements of the vector
 72  cout << "size of b = " << b . size() << '\n' ;
 73  
 74  b . reserve( 21 ) ; // pre allocate memory for 21 elements
 75  for ( int i=0 ; i < 21 ; ++i ) b . push_back( i ) ;
 76  
 77  vector<float> c(30) ;
 78  
 79  copy( b.begin(), b.end(), c.begin() ) ;
 80  //       ^          ^        ^
 81  //       +----------+        + "pointer" to the begin of the "destination" memory
 82  //  range to be copied
 83  // it is equivalent to
 84  for ( vector<float>::iterator i = b . begin(), j = c . begin() ; 
 85        i != b . end() ;
 86        ++i, ++j ) 
 87    *j = *i ;
 88  for ( int i = 0 ; i < b.size() ; ++i ) c[i] = b[i] ;
 89
 90  // simulation of a matrix
 91  vector<vector<float> > m ;
 92  
 93  // to allocate for a matrix 10x20
 94  m . resize(10) ; // allocate for 10 vector
 95  // C-way loop
 96  for ( int i = 0 ; i < m . size() ; ++i ) m[i] . resize(20) ;
 97  // STL-way loop
 98  for ( vector<vector<float> >::iterator i = m.begin() ;
 99        i != m . end() ; ++i ) i -> resize(20) ;
100        
101   m[1][3] = 123 ; // m[1] access to 2nd element of m which is a vector
102                   // m[1][3] access to 3rd element of vector m[1].
103
104}

The ``dqueue`` container

File stl2.cc

 1/*
 2
 3  Example of use of STL (Standard Template Library)
 4  
 5  the dqueue container
 6
 7 */
 8
 9#include <iostream> // for I/O
10#include <string>   // string support
11#include <cmath>    // for sin, cos, ...
12
13#include <deque>      // the definition of STL deque container
14#include <algorithm>  // the definition of the STL algorithm (sort, find,...)
15
16using namespace std ;
17
18int
19main() {
20  // define a as a vector of int
21  deque<int> a ;
22  
23  a . push_back(12) ;
24  a . push_front(4) ;
25  
26  cout << "a.front() = " << a.front() << '\n' ; // the first element
27  cout << "a.back()  = " << a.back() << '\n' ; // the last element
28
29  cout << "size of a = " << a . size() << '\n' ;
30
31  // define b as a vector of 10 float
32  deque<float> b(10) ;
33
34  cout << "size of b = " << b . size() << '\n' ;
35  
36  b[2] = 30 ; // random access to the element of b 
37  b[5] = 12 ; // implemented internally by a loop!
38  b[9] = 1.34 ;
39
40  // loop on the vector STL-style way
41  for ( deque<float>::iterator i = b . begin() ;
42        i != b . end() ;
43        ++i ) // increment the iterator to "point" to the next object in 
44              // the vector b (an instance of vector<int>)
45    cout << *i << '\n' ;
46    //                              ^
47    //                              |
48    // access to the element of vector b pointed by iterator i
49
50  // Algorithms
51  
52  cout << "do sort\n" ;
53
54  sort( b.begin(), b.end() ) ; // now use merge sort not quick sort
55  //reverse( b.begin(), b.end() ) ;
56  //sort( b.rbegin(), b.rend() ) ;
57
58  for ( deque<float>::iterator i = b . begin() ; i != b . end() ; ++i ) 
59    cout << *i << '\n' ;
60
61  deque<float>::iterator i = max_element( b.begin(), b.end() ) ;
62  cout << "maximum element = " << *i << '\n' ;
63  
64  b . clear() ; // cancel all the elements of the vector
65  cout << "size of b = " << b . size() << '\n' ;
66
67  for ( int i=0 ; i < 21 ; ++i ) b . push_back( i ) ;  
68  deque<float> c(30) ;
69
70  copy( b.begin(), b.end(), c.begin() ) ;
71  //       ^          ^        ^
72  //       +----------+        + "pointer" to the begin of the "destination" memory
73  //  range to be copied
74  // it is equivalent to
75
76  for ( deque<float>::iterator i = b . begin(), j = c . begin() ; 
77        i != b . end() ;
78        ++i, ++j ) 
79    *j = *i ;
80  for ( int i = 0 ; i < b.size() ; ++i ) c[i] = b[i] ;
81}

the set container

File stl3.cc

 1/*
 2
 3  Example of use of STL (Standard Template Library)
 4  
 5  the set container
 6
 7 */
 8
 9#include <iostream> // for I/O
10#include <string>   // string support
11#include <cmath>    // for sin, cos, ...
12
13#include <set>        // the definition of STL set container
14#include <algorithm>  // the definition of the STL algorithm (sort, find,...)
15
16using namespace std ;
17
18int
19main() {
20  // define a as a vector of int
21  set<int> a ;
22
23  a . insert(12) ;
24  a . insert(4) ;
25  a . insert(4) ;
26  a . insert(4) ;
27  a . insert(4) ;
28  a . insert(4) ;
29  
30  cout << "size of a = " << a . size() << '\n' ;
31
32  // loop on the vector STL-style way
33  for ( set<int>::iterator i = a . begin() ;
34        i != a . end() ;
35        ++i ) // increment the iterator to "point" to the next object in 
36              // the vector b (an instance of vector<int>)
37    cout << *i << '\n' ;
38    //                              ^
39    //                              |
40    // access to the element of vector b pointed by iterator i
41
42  multiset<int> b ;
43
44  b . insert(12) ;
45  b . insert(4) ;
46  b . insert(4) ;
47  b . erase(4) ;
48  b . insert(4) ;
49  b . insert(4) ;
50  b . insert(4) ;
51  
52  cout << "size of b = " << b . size() << '\n' ;
53
54  // loop on the vector STL-style way
55  for ( multiset<int>::iterator i = b . begin() ;
56        i != b . end() ;
57        ++i ) // increment the iterator to "point" to the next object in 
58              // the vector b (an instance of vector<int>)
59    cout << *i << '\n' ;
60    //                              ^
61    //                              |
62    // access to the element of vector b pointed by iterator i
63
64  multiset<int>::iterator i = max_element( b . begin(), b . end() ) ;
65}