в 14:21, 25 мая 2010

2010-05-25T14:21:06Z

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2010-05-25T10:27:46Z

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==Call member function for each element in vector==

<source lang="cpp">

/* 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.
*/
//#define mem_fun1 mem_fun
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <functional>

class Person {
private:
std::string name;
public:
//...
void print () const {
std::cout << name << std::endl;
}
void printWithPrefix (std::string prefix) const {
std::cout << prefix << name << std::endl;
}
};
void foo (const std::vector<Person>& coll)
{
using std::for_each;
using std::bind2nd;
using std::mem_fun_ref;
// call member function print() for each element
for_each (coll.begin(), coll.end(), mem_fun_ref(&Person::print));
// call member function printWithPrefix() for each element
// - "person: " is passed as an argument to the member function
for_each (coll.begin(), coll.end(),bind2nd(mem_fun_ref(&Person::printWithPrefix),"person: "));
}

void ptrfoo (const std::vector<Person*>& coll)
// ^^^ pointer !
{
using std::for_each;
using std::bind2nd;
using std::mem_fun;
// call member function print() for each referred object
for_each (coll.begin(), coll.end(),
mem_fun(&Person::print));
// call member function printWithPrefix() for each referred object
// - "person: " is passed as an argument to the member function
for_each (coll.begin(), coll.end(),bind2nd(mem_fun(&Person::printWithPrefix),"person: "));
}

int main()
{
std::vector<Person> coll(5);
foo(coll);
std::vector<Person*> coll2;
coll2.push_back(new Person);
ptrfoo(coll2);
}
/*

person:
person:
person:
person:
person:
person:
*/

</source>

==Getting a C-Style Array from a Vector==

<source lang="cpp">
#include <numeric>
#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;
}
}
void doubler( int a[], int length ){
for( int i = 0; i < length; ++i )
a[i] *= 2;
}
int main( ){
vector<int> data( 5, 1 );
partial_sum( data.begin(), data.end(), data.begin() );
print( data );
if( !data.empty() ) {
doubler( &data[0], static_cast<int>( data.size() ) );
print( data );
}
}

</source>

==Sort vector of user-defined values==

<source lang="cpp">
#include <algorithm>
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
#include <utility>
using namespace std;
typedef pair<int,string> Pair;
inline bool less_than_second( const Pair& b1, const Pair& b2 ){
return b1.second < b2.second;
}
int main( )
{
const char* names[] = { "A","B", "C", "D","E" };
const int values[] = { 18, 20, 26, 30, 41 };
const int num_pairs = sizeof( names ) / sizeof( names[0] );
vector<Pair> pair( num_pairs );
transform( values, values+num_pairs, names,pair.begin(), make_pair<int,string> );
sort( pair.begin(), pair.end() );
vector<Pair>::const_reverse_iterator pair_rend = pair.rend();

for( vector<Pair>::const_reverse_iterator i= pair.rbegin(); i != pair_rend; ++i )
cout << i->first << " - " << i->second;
sort( pair.begin(), pair.end(), less_than_second );
vector<Pair>::const_iterator pair_end = pair.end();
for( vector<Pair>::const_iterator i = pair.begin();
i != pair_end; ++i )
cout << i->second << " - $" << i->first << " values\n";
}

</source>

==Store user-defined objects in a vector.==

<source lang="cpp">
#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
using namespace std;

class Employee {
string name;
unsigned number;
public:
Employee() { name = ""; number = 0; }
Employee(string n, unsigned num) {
name = n;
number = num;
}
string get_name() { return name; }
unsigned get_number() { return number; }
};
void show(vector<Employee> vect) {
vector<Employee>::iterator itr;
for(itr=vect.begin(); itr != vect.end(); ++itr)
cout << itr->get_number() << " " << itr->get_name() << endl;;
}
int main()
{
vector<Employee> employeeList;
employeeList.push_back(Employee("A", 9));
employeeList.push_back(Employee("B", 8));
employeeList.push_back(Employee("C", 6));
employeeList.push_back(Employee("D", 1));
show(employeeList);
return 0;
}

</source>

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