C++ Tutorial/vector/vector size

Computing the sum with template iterators

<source lang="cpp">#include <iostream>

1. 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;

}</source>

3 months on record
vectorSum number of sunny days: 34

Demonstration of size() and capacity()

<source lang="cpp">#include <iostream>

1. 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;

}</source>

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

<source lang="cpp">#include <iostream>

1. include <vector>
2. 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;

}</source>

Show statistics about vector: size, max_size and capacity

<source lang="cpp">#include <iostream>

1. 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;
}</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.
*/

1. include <iostream>
2. include <vector>
3. include <string>
4. include <algorithm>
5. 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;

}</source>

Hello, how are you ?
  max_size(): 1073741823
  size():     5
  capacity(): 5

vector size before and after elements insertion

<source lang="cpp">#include <iostream>

1. include <vector>
2. 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;

}</source>

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