C++ Tutorial/vector/vector capacity

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Demonstrating the STL vector capacity

#include <iostream>
#include <cassert>
#include <vector>
using namespace std;
int main()
{
  int N = 10000; // size of vectors
  vector<int> vector1, vector2;
  for (int k = 0; k != N; ++k) {
    vector<int>::size_type cap = vector1.capacity();
    vector1.push_back(k);
    if (vector1.capacity() != cap)
      cout << "k: " << k << ", new capacity: " << vector1.capacity() << endl;
  }
  return 0;
}
k: 0, new capacity: 1
k: 1, new capacity: 2
k: 2, new capacity: 4
k: 4, new capacity: 8
k: 8, new capacity: 16
k: 16, new capacity: 32
k: 32, new capacity: 64
k: 64, new capacity: 128
k: 128, new capacity: 256
k: 256, new capacity: 512
k: 512, new capacity: 1024
k: 1024, new capacity: 2048
k: 2048, new capacity: 4096
k: 4096, new capacity: 8192
k: 8192, new capacity: 16384

Demonstrating the STL vector capacity and reserve functions

#include <iostream>
#include <cassert>
#include <vector>
using namespace std;
int main()
{
  int N = 10000; // size of vectors
  vector<int> vector1, vector2;
  for (int k = 0; k != N; ++k) {
    vector<int>::size_type cap = vector1.capacity();
    vector1.push_back(k);
    if (vector1.capacity() != cap)
      cout << "k: " << k << ", new capacity: " << vector1.capacity() << endl;
  }
  vector2.reserve(N);
  for (int k = 0; k != N; ++k) {
    vector<int>::size_type cap = vector2.capacity();
    vector2.push_back(k);
    if (vector2.capacity() != cap)
      cout << "k: " << k << ", new capacity: " << vector2.capacity() << "\n";
  }
  return 0;
}
k: 0, new capacity: 1
k: 1, new capacity: 2
k: 2, new capacity: 4
k: 4, new capacity: 8
k: 8, new capacity: 16
k: 16, new capacity: 32
k: 32, new capacity: 64
k: 64, new capacity: 128
k: 128, new capacity: 256
k: 256, new capacity: 512
k: 512, new capacity: 1024
k: 1024, new capacity: 2048
k: 2048, new capacity: 4096
k: 4096, new capacity: 8192
k: 8192, new capacity: 16384

make a big vector and then deallocate all its memory

#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
int main( )
{
   // make a big vector and then deallocate all its memory
   const int big_size = 10000;
   vector<double> v( big_size );
   cout << "Before clearing, the capacity of the vector is "
      << v.capacity() << " and its size is " << v.size();
   v.clear();
   cout << "\nAfter clearing, the capacity of the vector is "
      << v.capacity() << " and its size is " << v.size();
   vector<double>().swap( v );
   cout << "\nAfter swapping, the capacity of the vector is "
      << v.capacity() << " and its size is " << v.size();
}

make a big vector and then minimize its memory

#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
int main( )
{
   const int big_size = 10000;
   vector<double> v( big_size );
   // make a big vector and then minimize its memory
   v.assign( big_size, 3.33 );
   cout << "\n\nBefore resizing, the capacity of the vector is "
      << v.capacity() << " and its size is " << v.size();
   v.resize( 1 );
   cout << "\nAfter resizing, the capacity of the vector is "
      << v.capacity() << " and its size is " << v.size();
   vector<double>( v ).swap( v );
   cout << "\nAfter swapping, the capacity of the vector is "
      << v.capacity() << " and its size is " << v.size();
}

make the vector as large as possible without reallocating

#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
template <class T>
void print(T& c){
   for( typename T::iterator i = c.begin(); i != c.end(); i++ ){
      std::cout << *i << endl;
   }
}
int main( )
{
   vector<double> v( 5, 2.78 );
   v[2] = 0.0;
   // make the vector as large as possible without reallocating
   v.resize( v.capacity(), 2.78 );
}
Источник — «http://cppe.ru/index.php?title=C%2B%2B_Tutorial/vector/vector_capacity&oldid=2233»