C++ Tutorial/vector/vector reserve — различия между версиями
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Текущая версия на 10:29, 25 мая 2010
Ensure there"s room for at least 1000 elements
#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);
// Ensure there"s room for at least 1000 elements.
theVector.reserve(1000);
cout << endl << "After reserving storage for 1000 elements:" << endl;
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;
}Reserve memory for five elements to avoid reallocation
/* 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;
}Hello, how are you ?
Reserving Space in a Vector
#include <vector>
using namespace std;
int main( )
{
// fill a vector with one million numbers the slow way
vector<int> v1;
for( int i = 0; i < 1000000; ++i )
v1.push_back( i );
// fill a vector with one million numbers the fast way
vector<int> v2; // has zero elements
v2.reserve( 1000000 ); // still has zero elements
for( int i = 0; i < 1000000; ++i )
v2.push_back( i );
}