remove_if(3C++) - remove_if(3C++)
Standard C++ Library Copyright 1998, Rogue Wave Software, Inc.
NAMEremove_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 corre‐
sponding condition holds: pred(*i) == true. remove_if returns an itera‐
tor 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 actu‐
ally: 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. Elements 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 fol‐
lowing 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 Output1 2 3 4 5 6 7 8 9 101 2 3 4 5 6 8 9 101 2 3 41 2 4WARNINGS
If your compiler does not support default template parameters, 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
Rogue Wave Software 02 Apr 1998 remove_if(3C++)
