Просмотр исходного текста страницы C++/Vector/vector size

==Computing the sum with template iterators==


   
<source lang="cpp">  
 
#include <iostream>
#include <vector> 
using std::cout;
using std::endl;
using std::vector;
template <typename Iter> 
double vectorSum(Iter begin, Iter end) {
  double sum = 0.0;
  while( begin != end )
    sum += *begin++;
  return sum;        
} 
int main() {
  vector<int> sunny;
  sunny.push_back(7);  
  sunny.push_back(12);  
  sunny.push_back(15);
  cout << sunny.size() << " months on record" << endl; 
  cout << "vectorSum number of sunny days: "; 
  cout << vectorSum(sunny.begin(), sunny.end()) << endl; 
  return 0;
}
/* 
3 months on record
vectorSum number of sunny days: 34
 */        
    
  </source>


==Make vector large enough to hold all value==


   
<source lang="cpp">  
#include <algorithm>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <string>
#include <vector>
using namespace std;
class PC
{
   public:
   enum part { keyboard, mouse, monitor };
   PC( part a_part = PC::keyboard, int id = 0 );
   bool operator<( const PC& rhs ) const;
   void print() const;
   private:
   part part_;
   int id_;
};
inline
PC::PC( part a_part, int id ) : part_( a_part ), id_( id ){}
inline bool PC::operator<( const PC& rhs ) const{  
   return id_ < rhs.id_; 
}
void PC::print() const {
   string component;
   if( part_ == keyboard )
      component = "keyboard";
   else if( part_ == mouse )
      component = "mouse";
   else
      component = "monitor";
   cout << "ID: " << setw( 8 ) << left << id_ << " PC: " << component << endl;
}
int main( )
{
   list<PC> listA;
   listA.push_back( PC( PC::keyboard, 3 ) );
   listA.push_back( PC( PC::mouse, 1 ) );
   listA.push_back( PC( PC::monitor, 9 ) );
   listA.push_back( PC( PC::keyboard, 2 ) );
   listA.push_back( PC( PC::monitor, 8 ) );
   list<PC> inspector_B( listA );
   inspector_B.front() = PC( PC::mouse, 6 );
   inspector_B.back() = PC( PC::monitor, 1 );
   // must sort before using set algorithms
   listA.sort();
   inspector_B.sort();
   vector<PC> result;
   result.resize( listA.size() + inspector_B.size() );
}
  
    
  </source>


==vector: max_size(), size(), capacity()==


   
<source lang="cpp">  
 
/* The following code example is taken from the book
 * "The C++ Standard Library - A Tutorial and Reference"
 * by Nicolai M. Josuttis, Addison-Wesley, 1999
 *
 * (C) Copyright Nicolai M. Josuttis 1999.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <iterator>
using namespace std;
int main()
{
    // create empty vector for strings
    vector<string> sentence;
    // reserve memory for five elements to avoid reallocation
    sentence.reserve(5);
    // append some elements
    sentence.push_back("Hello,");
    sentence.push_back("how");
    sentence.push_back("are");
    sentence.push_back("you");
    sentence.push_back("?");
    // print elements separated with spaces
    copy (sentence.begin(), sentence.end(),
          ostream_iterator<string>(cout," "));
    cout << endl;
    cout << "  max_size(): " << sentence.max_size() << endl;
    cout << "  size():     " << sentence.size()     << endl;
    cout << "  capacity(): " << sentence.capacity() << endl;
}
/* 
Hello, how are you ?
  max_size(): 1073741823
  size():     5
  capacity(): 5
 */
        
    
  </source>


==vector size before and after elements insertion==


   
<source lang="cpp">  
 
#include <iostream>
#include <vector>
#include <cctype>
using namespace std;
int main()
{
  vector<char> v(10); // create a vector of length 10
  cout << "Size = " << v.size() << endl;
  for(int i=0; i<10; i++)
     v[i] = i + "a";
  cout << "Current Contents:\n";
  for(int i=0; i<v.size(); i++) cout << v[i] << " ";
  cout << "\n\n";
  cout << "Expanding vector\n";
  for(int i=0; i<10; i++)
     v.push_back(i + 10 + "a");
  cout << "Size now = " << v.size() << endl;
  cout << "Current contents:\n";
  for(int i=0; i<v.size(); i++)
      cout << v[i] << " ";
  cout << "\n\n";
  return 0;
}
/* 
Size = 10
Current Contents:
a b c d e f g h i j
Expanding vector
Size now = 20
Current contents:
a b c d e f g h i j k l m n o p q r s t

 */
        
    
  </source>