C++ Tutorial/vector/vector size — различия между версиями

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Версия 14:21, 25 мая 2010

Computing the sum with template iterators

#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

Demonstration of size() and capacity()

#include <iostream>
#include <vector>
int main ()
{
    using namespace std;
    // Instantiate a vector object that holds 5 integers of default value
    vector <int> v (5);
    cout << "Size: " << v.size ();
    cout << ", Capacity: " <<  v.capacity () << endl;
    // Inserting a 6th element in to the vector
    v.push_back (666);
    cout << "Size: " << v.size ();
    cout << ", Capacity: " <<  v.capacity () << endl;
    // Inserting another element
    v.push_back (777);
    cout << "After inserting yet another element... " << endl;
    cout << "Size: " << v.size ();
    cout << ", Capacity: " <<  v.capacity () << endl;
    return 0;
}

Put more values onto the end of the vector,it will grow as needed

#include <iostream>
#include <vector>
#include <cctype>
using namespace std;
   
int main()
{
  vector<char> v(10); // create a vector of length 10
  unsigned int i;
   
  // display original size of v
  cout << "Size = " << v.size() << endl;
   
  // assign the elements of the vector some values
  for(i=0; i<10; i++) v[i] = i + "a";
   
  // display contents of vector
  cout << "Current Contents:\n";
  for(i=0; i<v.size(); i++) cout << v[i] << " ";
  cout << "\n\n";
   
  cout << "Expanding vector\n";
  
  for(i=0; i<10; i++) v.push_back(i + 10 + "a");
   
  // display current size of v
  cout << "Size now = " << v.size() << endl;
   
  // display contents of vector
  cout << "Current contents:\n";
  for(i=0; i<v.size(); i++) cout << v[i] << " ";
  cout << "\n\n";
   
  // change contents of vector
  for(i=0; i<v.size(); i++) v[i] = toupper(v[i]);
  cout << "Modified Contents:\n";
  for(i=0; i<v.size(); i++) cout << v[i] << " ";
  cout << endl;
   
  return 0;
}

Show statistics about vector: size, max_size and capacity

#include <iostream>
#include <vector>
using namespace std;
typedef vector<int> INTVECTOR;
int main(void)
 {
   // Dynamically allocated vector begins with 0 elements.
   INTVECTOR theVector;
   theVector.push_back(42);
   // Show statistics about vector.
   cout << "theVector"s size is: " << theVector.size() << endl;
   cout << "theVector"s maximum size is: " << theVector.max_size()<< endl;
   cout << "theVector"s capacity is: " << theVector.capacity() << endl;
 }

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

/* 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

vector size before and after elements insertion

#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
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