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                       Standard C++ Library
             Copyright 1998, Rogue Wave Software, Inc.


NAME
     remove_if

      - Moves desired elements to the front of a  container,  and
     returns  an  iterator  that  describes where the sequence of
     desired elements ends.



SYNOPSIS
     #include <algorithm>
     template <class ForwardIterator, class Predicate>
     ForwardIterator remove_if (ForwardIterator first,
                               ForwardIterator last,
                               Predicate pred);



DESCRIPTION
     The remove_if algorithm eliminates all the elements referred
     to  by  iterator  i in the range [first, last) for which the
     following corresponding condition holds: pred(*i)  ==  true.
     remove_if  returns an iterator that points to the end of the
     resulting range. remove_if is stable, which means  that  the
     relative  order  of the elements that are not removed is the
     same as their relative order in the original range.

     remove_if does not actually reduce the size of the sequence.
     It actually: 1) copies the values that are to be retained to
     the front of the sequence, and 2) returns an  iterator  that
     describes  where  the sequence of retained values ends. Ele-
     ments that follow this  iterator  are  simply  the  original
     sequence values, left unchanged. Here's a simple example:

     Say we want to remove all even numbers  from  the  following
     sequence:

           123456789

     Applying the remove_if algorithm results  in  the  following
     sequence:

           13579|XXXX

     The vertical bar represents the  position  of  the  iterator
     returned by remove_if. Note that the elements to the left of
     the vertical bar are the original  sequence  with  the  even
     numbers  removed.  The  elements to the right of the bar are
     simply  the  untouched  original  members  of  the  original
     sequence.

     If you want to actually delete items from the container, use
     the following technique:

     container.erase(remove(first,last,value),container.end());



COMPLEXITY
     Exactly last1 - first1  applications  of  the  corresponding
     predicate are done.



EXAMPLE
     //
     // remove.cpp
     //
      #include <algorithm>
      #include <vector>
      #include <iterator>
      #include <iostream>
     using namespace std;
     template<class Arg>
     struct all_true : public unary_function<Arg, bool>
      {
       bool operator()(const Arg& x){ return 1; }
      };
     int main ()
      {
       int arr[10] = {1,2,3,4,5,6,7,8,9,10};
       vector<int> v(arr, arr+10);
       copy(v.begin(),v.end(),
            ostream_iterator<int,char>(cout," "));
       cout << endl << endl;
        // remove the 7
       vector<int>::iterator result =
               remove(v.begin(), v.end(), 7);
        // delete dangling elements from the vector
       v.erase(result, v.end());
       copy(v.begin(),v.end(),
            ostream_iterator<int,char>(cout," "));
       cout << endl << endl;
        // remove everything beyond the fourth element
       result = remove_if(v.begin()+4,
                          v.begin()+8, all_true<int>());

        // delete dangling elements
       v.erase(result, v.end());
       copy(v.begin(),v.end(),
            ostream_iterator<int,char>(cout," "));
       cout << endl << endl;
       return 0;
      }

     Program Output



     1 2 3 4 5 6 7 8 9 10
     1 2 3 4 5 6 8 9 10
     1 2 3 4
     1 2 4



WARNINGS
     If your compiler does not support default  template  parame-
     ters,  then you always need to supply the Allocator template
     argument. For instance, you need to write:

     vector<int, allocator<int> >

     instead of:

     vector<int>

     If your compiler does not support namespaces,  then  you  do
     not need the using declaration for std.



SEE ALSO
     remove, remove_copy, remove_copy_if

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