C++/STL Algorithms Modifying sequence operations/remove if — различия между версиями
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Версия 14:21, 25 мая 2010
remove_if for list
/* 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 <list>
#include <algorithm>
using namespace std;
/* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by
* - all elements of the collection coll
* - separated by spaces
*/
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
typename T::const_iterator pos;
std::cout << optcstr;
for (pos=coll.begin(); pos!=coll.end(); ++pos) {
std::cout << *pos << " ";
}
std::cout << std::endl;
}
class Nth { // function object that returns true for the nth call
private:
int nth; // call for which to return true
int count; // call counter
public:
Nth (int n) : nth(n), count(0) {
}
bool operator() (int) {
return ++count == nth;
}
};
int main()
{
list<int> coll;
// insert elements from 1 to 9
for (int i=1; i<=9; ++i) {
coll.push_back(i);
}
PRINT_ELEMENTS(coll,"coll: ");
// remove third element
list<int>::iterator pos;
pos = remove_if(coll.begin(),coll.end(), // range
Nth(3)); // remove criterion
coll.erase(pos,coll.end());
PRINT_ELEMENTS(coll,"nth removed: ");
}
/*
coll: 1 2 3 4 5 6 7 8 9
nth removed: 1 2 4 5 7 8 9
*/
Removing All Matching Elements
#include <algorithm>
#include <functional>
#include <iostream>
#include <iterator>
#include <numeric>
#include <vector>
using namespace std;
int main( )
{
const int last_number = 50;
vector<int> v( last_number - 1, 1 );
v[0] = 2;
partial_sum( v.begin(), v.end(), v.begin() );
vector<int>::iterator stop = v.end();
for( vector<int>::iterator start = v.begin(); start != stop;++start )
// remove all subsequent numbers that are not divisible by the current one
stop = remove_if( start+1, stop,not1( bind2nd( modulus<int>(), *start ) ) );
cout << "Prime numbers: ";
copy( v.begin(), stop, ostream_iterator<int>( cout, " " ) );
}
Use predicate in std::remove_if
#include <iostream>
using std::cout;
using std::endl;
#include <algorithm>
#include <vector>
#include <iterator>
bool greater9( int );
int main()
{
int a[ 10 ] = { 10, 2, 10, 4, 16, 6, 14, 8, 12, 10 };
std::ostream_iterator< int > output( cout, " " );
std::vector< int > v3( a, a + 10 ); // copy of a
cout << "Vector v3 before removing all elements"
<< "\ngreater than 9:\n ";
std::copy( v3.begin(), v3.end(), output );
// remove elements greater than 9 from v3
std::vector< int >::iterator newLastElement = std::remove_if( v3.begin(), v3.end(), greater9 );
cout << "\nVector v3 after removing all elements"
<< "\ngreater than 9:\n ";
std::copy( v3.begin(), newLastElement, output );
return 0;
}
bool greater9( int x )
{
return x > 9;
}
/*
Vector v3 before removing all elements
greater than 9:
10 2 10 4 16 6 14 8 12 10
Vector v3 after removing all elements
greater than 9:
2 4 6 8
*/