Almeno nel mio compilatore, i vettori non sembrano ridurre il loro spazio allocato. Quando eseguo:
std::vector<int> v;
for(unsigned x=0;x<20;++x)
{
v.push_back(x);
out << "elements: " << v.size() << ", capacity: " << v.capacity() << std::endl;
}
for(unsigned x=v.size();x>0;--x)
{
v.pop_back();
out << "elements: " << v.size() << ", capacity: " << v.capacity() << std::endl;
}
cosa viene restituito è:
elements: 1, capacity: 1
elements: 2, capacity: 2
elements: 3, capacity: 4
elements: 4, capacity: 4
elements: 5, capacity: 8
elements: 6, capacity: 8
elements: 7, capacity: 8
elements: 8, capacity: 8
elements: 9, capacity: 16
elements: 10, capacity: 16
elements: 11, capacity: 16
elements: 12, capacity: 16
elements: 13, capacity: 16
elements: 14, capacity: 16
elements: 15, capacity: 16
elements: 16, capacity: 16
elements: 17, capacity: 32
elements: 18, capacity: 32
elements: 19, capacity: 32
elements: 20, capacity: 32
elements: 19, capacity: 32
elements: 18, capacity: 32
elements: 17, capacity: 32
elements: 16, capacity: 32
elements: 15, capacity: 32
elements: 14, capacity: 32
elements: 13, capacity: 32
elements: 12, capacity: 32
elements: 11, capacity: 32
elements: 10, capacity: 32
elements: 9, capacity: 32
elements: 8, capacity: 32
elements: 7, capacity: 32
elements: 6, capacity: 32
elements: 5, capacity: 32
elements: 4, capacity: 32
elements: 3, capacity: 32
elements: 2, capacity: 32
elements: 1, capacity: 32
elements: 0, capacity: 32
Lo standard non lo fa conferire la capacità di raddoppiare la riallocazione. Significa solo che la crescita deve essere geometrica per ottenere l'inserimento del tempo costante ammortizzato. Ma qualsiasi fattore di crescita α> 1 si qualificherà per quello. – 5gon12eder