remove_if

Article
07/29/2015

Eliminates elements that satisfy a predicate from a given range without disturbing the order of the remaining elements and returning the end of a new range free of the specified value.

template<class ForwardIterator, class Predicate> 
   ForwardIterator remove_if( 
      ForwardIterator _First,  
      ForwardIterator _Last, 
      Predicate _Pred 
   );

Parameters

_First
A forward iterator pointing to the position of the first element in the range from which elements are being removed.
_Last
A forward iterator pointing to the position one past the final element in the range from which elements are being removed.
_Pred
The unary predicate that must be satisfied is the value of an element is to be replaced.

Return Value

A forward iterator addressing the new end position of the modified range, one past the final element of the remnant sequence free of the specified value.

Remarks

The range referenced must be valid; all pointers must be dereferenceable and within the sequence the last position is reachable from the first by incrementation.

The order of the elements not removed remains stable.

The operator== used to determine the equality between elements must impose an equivalence relation between its operands.

The complexity is linear: there are (_Last – _First) comparisons for equality.

List has a more efficient member function version of remove which relinks pointers.

Example

// alg_remove_if.cpp
// compile with: /EHsc
#include <vector>
#include <algorithm>
#include <iostream>

bool greater6 ( int value ) {
   return value >6;
}

int main( ) {
   using namespace std;
   vector <int> v1, v2;
   vector <int>::iterator Iter1, Iter2, new_end;

   int i;
   for ( i = 0 ; i <= 9 ; i++ )
      v1.push_back( i );

   int ii;
   for ( ii = 0 ; ii <= 3 ; ii++ )
      v1.push_back( 7 );
   
   random_shuffle ( v1.begin( ), v1.end( ) );
   cout << "Vector v1 is ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
      cout << *Iter1 << " ";
   cout << ")." << endl;

   // Remove elements satisfying predicate greater6
   new_end = remove_if (v1.begin( ), v1.end( ), greater6 );

   cout << "Vector v1 with elements satisfying greater6 removed is\n ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
      cout << *Iter1 << " ";
   cout << ")." << endl;

   // To change the sequence size, use erase
   v1.erase (new_end, v1.end( ) );

   cout << "Vector v1 resized elements satisfying greater6 removed is\n ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
      cout << *Iter1 << " ";
   cout << ")." << endl;
}

Sample Output

Vector v1 is ( 7 1 9 2 0 7 7 3 4 6 8 5 7 7 ).
Vector v1 with elements satisfying greater6 removed is
 ( 1 2 0 3 4 6 5 3 4 6 8 5 7 7 ).
Vector v1 resized elements satisfying greater6 removed is
 ( 1 2 0 3 4 6 5 ).

Requirements

Header: <algorithm>

Namespace: std

Share via