remove_if for list : remove_if « STL Algorithms Modifying sequence operations « C++ Tutorial

1. C++ Tutorial
2. STL Algorithms Modifying sequence operations
3. remove_if

/* 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