C++ Tutorial/vector/vector capacity — различия между версиями
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Версия 14:21, 25 мая 2010
Содержание
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 );
}