C++ Tutorial/vector/vector iterator — различия между версиями
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Версия 14:21, 25 мая 2010
Содержание
- 1 Change contents of vector through an iterator
- 2 Const iterators
- 3 Converting Between Iterators and Indexes in a Vector
- 4 Cycle through v in the forward direction using an iterator.
- 5 Cycle through v in the reverse direction using a reverse_iterator.
- 6 Declare an iterator to a vector<char>
- 7 Display contents of vector through an iterator
- 8 iterators for vector
- 9 Loop through all elements in a vector in reverse order by using rbegn, rend
- 10 Obtain an iterator to the start of vector
- 11 Reverse iterators
- 12 See if iterator is still in the same spot of memory
- 13 Use const_iterator to loop through the vector
Change contents of vector through an iterator
#include <iostream>
#include <vector>
#include <cctype>
using namespace std;
int main()
{
vector<char> v(10); // create a vector of length 10
vector<char>::iterator p; // create an iterator
int i;
// assign elements in vector a value
p = v.begin();
i = 0;
while(p != v.end()) {
*p = i + "a";
p++;
i++;
}
// display contents of vector
cout << "Original contents:\n";
p = v.begin();
while(p != v.end()) {
cout << *p << " ";
p++;
}
cout << "\n\n";
// change contents of vector
p = v.begin();
while(p != v.end()) {
*p = toupper(*p);
p++;
}
// display contents of vector
cout << "Original contents:\n";
p = v.begin();
while(p != v.end()) {
cout << *p << " ";
p++;
}
cout << "\n\n";
return 0;
}Original contents: a b c d e f g h i j Original contents: A B C D E F G H I J
Const iterators
#include <vector>
#include <iostream>
using namespace std;
vector<double> makevector(int size){
vector<double> result;
for (int i=1; i<=size; i++) {
result.push_back(double(i));
}
return result;
}
void print(const vector<double>& l)
{
cout << "Size of vector is: " << l.size() << endl;
vector<double>::const_iterator i;
for (i=l.begin(); i!=l.end(); i++)
{
cout << (*i) << " ";
}
cout << endl;
}
int main()
{
vector<double> vector1=makevector(5);
vector<double>::iterator bi;
// Change element with const iterator
cout << "Change first element with const iterator" << endl;
vector<double>::const_iterator ci;
ci=vector1.end();
ci--;
cout << *ci << endl;
}Converting Between Iterators and Indexes in a Vector
#include <algorithm>
#include <string>
#include <vector>
#include <iostream>
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( )
{
const char* name_array[] = { "John", "Harry", "Mark", "Abe" };
const int age_array[] = { 89, 34, 12, 20 };
const int people = sizeof( age_array ) / sizeof( age_array[0] );
// make vectors with names and ages
vector<string> names( name_array, name_array+people );
vector<int> ages( age_array, age_array+people );
// find the youngest age
vector<int>::iterator age_itr = min_element( ages.begin(), ages.end() );
// convert from iterator to index
cout << names[age_itr-ages.begin()]
<< ", the youngest person, is " << *age_itr << " years old\n";
// convert from index to iterator
print( names);
names.erase( names.begin()+1 ); // erase the second element
print( names);
}Cycle through v in the forward direction using an iterator.
#include <iostream>
#include <vector>
using namespace std;
void show(const char *msg, vector<int> vect);
int main() {
// Declare a vector that has an initial capacity of 10.
vector<int> v(10);
for(unsigned i=0; i < v.size(); ++i) v[i] = i*i;
show("Contents of v: ", v);
// the use of the subscripting operator.
int sum = 0;
for(unsigned i=0; i < v.size(); ++i) sum += v[i];
double avg = sum / v.size();
cout << "The average of the elements is " << avg << "\n\n";
// Add elements to the end of v.
v.push_back(100);
v.push_back(121);
show("v after pushing elements onto the end: ", v);
cout << endl;
// Now use pop_back() to remove one element.
v.pop_back();
show("v after back-popping one element: ", v);
cout << endl;
// Declare an iterator to a vector<int>.
vector<int>::iterator itr;
// Now, declare reverse iterator to a vector<int>
vector<int>::reverse_iterator ritr;
// Cycle through v in the forward direction using an iterator.
for(itr = v.begin(); itr != v.end(); ++itr)
cout << *itr << " ";
return 0;
}
void show(const char *msg, vector<int> vect) {
cout << msg << endl;
for(unsigned i=0; i < vect.size(); ++i)
cout << vect[i] << endl;
}Cycle through v in the reverse direction using a reverse_iterator.
#include <iostream>
#include <vector>
using namespace std;
void show(const char *msg, vector<int> vect);
int main() {
// Declare a vector that has an initial capacity of 10.
vector<int> v(10);
for(unsigned i=0; i < v.size(); ++i) v[i] = i*i;
// Create an empty vector and then assign it a sequence that is the reverse of v.
vector<int> v3;
v3.assign(v.rbegin(), v.rend());
show("v3 contains the reverse of v: ", v3);
// Show the size and capacity of v.
cout << "Size of v is " << v.size() << ". The capacity is " << v.capacity() << ".\n";
// Now, resize v.
v.resize(20);
cout << "After calling resize(20), the size of v is "
<< v.size() << " and the capacity is "
<< v.capacity() << ".\n";
// Now, reserve space for 50 elements.
v.reserve(50);
cout << "After calling reserve(50), the size of v is "
<< v.size() << " and the capacity is "
<< v.capacity() << ".\n";
return 0;
}
void show(const char *msg, vector<int> vect) {
cout << msg << endl;
for(unsigned i=0; i < vect.size(); ++i)
cout << vect[i] << endl;
}Declare an iterator to a vector<char>
#include <iostream>
#include <vector>
using namespace std;
void show(const char *msg, vector<char> vect);
int main() {
vector<char> v;
// Declare an iterator to a vector<char>.
vector<char>::iterator itr;
// Obtain an iterator to the start of v.
itr = v.begin();
return 0;
}
void show(const char *msg, vector<char> vect) {
vector<char>::iterator itr;
cout << msg << endl;
for(itr=vect.begin(); itr != vect.end(); ++itr)
cout << *itr << endl;
}Display contents of vector through an iterator
#include <iostream>
#include <vector>
#include <cctype>
using namespace std;
int main()
{
vector<char> v(10); // create a vector of length 10
vector<char>::iterator p; // create an iterator
int i;
// assign elements in vector a value
p = v.begin();
i = 0;
while(p != v.end()) {
*p = i + "a";
p++;
i++;
}
// display contents of vector
cout << "Original contents:\n";
p = v.begin();
while(p != v.end()) {
cout << *p << " ";
p++;
}
cout << "\n\n";
return 0;
}Original contents: a b c d e f g h i j
iterators for vector
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
vector<string> v;
v.push_back("A");
v.push_back("B");
v.push_back("C");
vector<string>::iterator myIterator;
vector<string>::const_iterator iter;
for (iter = v.begin(); iter != v.end(); ++iter)
cout << *iter << endl;
myIterator = v.begin();
*myIterator = "D";
for (iter = v.begin(); iter != v.end(); ++iter)
cout << *iter << endl;
cout << *myIterator << "" has ";
cout << (*myIterator).size() << " letters in it.\n";
cout << "\nThe item name "" << *myIterator << "" has ";
cout << myIterator->size() << " letters in it.\n";
v.insert(v.begin(), "A");
for (iter = v.begin(); iter != v.end(); ++iter)
cout << *iter << endl;
v.erase((v.begin() + 2));
for (iter = v.begin(); iter != v.end(); ++iter)
cout << *iter << endl;
return 0;
}Loop through all elements in a vector in reverse order by using rbegn, rend
/* 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 <algorithm>
#include <iterator>
using namespace std;
int main()
{
vector<int> coll;
// insert elements from 1 to 9
for (int i=1; i<=9; ++i) {
coll.push_back(i);
}
// print all element in reverse order
copy (coll.rbegin(), coll.rend(), // source
ostream_iterator<int>(cout," ")); // destination
cout << endl;
}9 8 7 6 5 4 3 2 1
Obtain an iterator to the start of vector
#include <iostream>
#include <vector>
using namespace std;
void show(const char *msg, vector<char> vect);
int main() {
vector<char> v;
// Declare an iterator to a vector<char>.
vector<char>::iterator itr;
// Obtain an iterator to the start of v.
itr = v.begin();
return 0;
}
void show(const char *msg, vector<char> vect) {
vector<char>::iterator itr;
cout << msg << endl;
for(itr=vect.begin(); itr != vect.end(); ++itr)
cout << *itr << endl;
}Reverse iterators
#include <vector>
#include <iostream>
using namespace std;
vector<double> makevector(int size){
vector<double> result;
for (int i=1; i<=size; i++) {
result.push_back(double(i));
}
return result;
}
void print(const vector<double>& l)
{
cout << "Size of vector is: " << l.size() << endl;
vector<double>::const_iterator i;
for (i=l.begin(); i!=l.end(); i++)
{
cout << (*i) << " ";
}
cout << endl;
}
int main()
{
vector<double> vector1=makevector(5);
vector<double>::iterator bi;
// Create bidirectional iterator
vector<double>::reverse_iterator ri;
// Traverse reverse forward
cout << "Traverse reverse forward" << endl;
ri=vector1.rbegin(); // Set iterator
while (ri!=vector1.rend()) cout << (*ri++) << " ";
cout << endl << endl;
// Traverse reverse backward
cout << "Traverse reverse backward" << endl;
ri=(vector1.rend());
do
{
cout << (*--ri) << " ";
}
while (ri!=vector1.rbegin());
cout << endl << endl;
// Traverse reverse random
cout << "Traverse reverse random" << endl;
cout << *ri << " "; // First element
cout << *(ri+=3) << " "; // 1+3 is 4th element
cout << *(ri-=1) << " "; // 4-1 is third element
cout << ri[-1] << " "; // 3-1 is second element
cout << ri[1] << endl << endl; // 3+1 is fourth element
}See if iterator is still in the same spot of memory
#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 );
// find the smallest number
vector<double>::iterator before_itr = min_element( v.begin(), v.end() );
// append one more element. This causes reallocation
v.push_back( 2.78 );
// find the smallest number. (Its value is the same as before.)
vector<double>::iterator after_itr = min_element( v.begin(), v.end() );
// See if minimum is still in the same spot of memory
if( before_itr == after_itr )
cout << "The iterators are the same";
else
cout << "The iterators are not the same";
}Use const_iterator to loop through the vector
#include <iostream>
using std::cout;
using std::endl;
#include <vector>
using std::vector;
int main()
{
int array[ 6 ] = { 1, 2, 3, 4, 5, 6 }; // initialize array
vector< int > integers; // create vector of ints
integers.push_back( 2 );
integers.push_back( 3 );
integers.push_back( 4 );
vector< int >::const_iterator constIterator;
// display vector elements using const_iterator
for ( constIterator = integers.begin();
constIterator != integers.end(); ++constIterator )
cout << *constIterator << " ";
cout << endl;
return 0;
}2 3 4
