find_first_of

Searches for the first occurrence of any of several values within a target range or for the first occurrence of any of several elements that are equivalent in a sense specified by a binary predicate to a specified set of the elements.

template<class ForwardIterator1, class ForwardIterator2> 
   ForwardIterator1 find_first_of( 
      ForwardIterator1 _First1,  
      ForwardIterator1 _Last1, 
      ForwardIterator2 _First2,  
      ForwardIterator2 _Last2 
   ); 
template<class ForwardIterator1, class ForwardIterator2, class BinaryPredicate> 
   ForwardIterator1 find_first_of( 
      ForwardIterator1 _First1,  
      ForwardIterator1 _Last1, 
      ForwardIterator2 _First2,  
      ForwardIterator2 _Last2, 
      BinaryPredicate _Comp 
   );

Parameters

• _First1
  A forward iterator addressing the position of the first element in the range to be searched.

• _Last1
  A forward iterator addressing the position one past the final element in the range to be searched.

• _First2
  A forward iterator addressing the position of the first element in the range to be matched.

• _Last2
  A forward iterator addressing the position one past the final element in the range to be matched.

• _Comp
  User-defined predicate function object that defines the condition to be satisfied if two elements are to be taken as equivalent. A binary predicate takes two arguments and returns true when satisfied and false when not satisfied.

Return Value

A forward iterator addressing the position of the first element of the first subsequence that matches the specified sequence or that is equivalent in a sense specified by a binary predicate.

Remarks

The operator== used to determine the match between an element and the specified value must impose an equivalence relation between its operands.

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

Example

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

// Return whether second element is twice the first
bool twice ( int elem1, int elem2 )
{
   return 2 * elem1 == elem2;
}

int main( )
{
   using namespace std;
   vector <int> v1, v2;
   list <int> L1;
   vector <int>::iterator Iter1, Iter2;
   list <int>::iterator L1_Iter, L1_inIter;

   int i;
   for ( i = 0 ; i <= 5 ; i++ )
   {
      v1.push_back( 5 * i );
   }
   for ( i = 0 ; i <= 5 ; i++ )
   {
      v1.push_back( 5 * i );
   }

   int ii;
   for ( ii = 3 ; ii <= 4 ; ii++ )
   {
      L1.push_back( 5 * ii );
   }

   int iii;
   for ( iii = 2 ; iii <= 4 ; iii++ )
   {
      v2.push_back( 10 * iii );
   }

   cout << "Vector v1 = ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
      cout << *Iter1 << " ";
   cout << ")" << endl;

   cout << "List L1 = ( " ;
   for ( L1_Iter = L1.begin( ) ; L1_Iter!= L1.end( ) ; L1_Iter++ )
      cout << *L1_Iter << " ";
   cout << ")" << endl;

   cout << "Vector v2 = ( " ;
   for ( Iter2 = v2.begin( ) ; Iter2 != v2.end( ) ; Iter2++ )
      cout << *Iter2 << " ";
      cout << ")" << endl;

   // Searching v1 for first match to L1 under identity
   vector <int>::iterator result1;
   result1 = find_first_of ( v1.begin( ), v1.end( ), L1.begin( ), L1.end( ) );

   if ( result1 == v1.end( ) )
      cout << "There is no match of L1 in v1."
           << endl;
   else
      cout << "There is at least one match of L1 in v1"
           << "\n and the first one begins at "
           << "position "<< result1 - v1.begin( ) << "." << endl;

   // Searching v1 for a match to L1 under the binary predicate twice
   vector <int>::iterator result2;
   result2 = find_first_of ( v1.begin( ), v1.end( ), v2.begin( ), v2.end( ), twice );

   if ( result2 == v1.end( ) )
      cout << "There is no match of L1 in v1."
           << endl;
   else
      cout << "There is a sequence of elements in v1 that "
           << "are equivalent\n to those in v2 under the binary "
           << "predicate twice\n and the first one begins at position "
           << result2 - v1.begin( ) << "." << endl;
}

Vector v1 = ( 0 5 10 15 20 25 0 5 10 15 20 25 )
List L1 = ( 15 20 )
Vector v2 = ( 20 30 40 )
There is at least one match of L1 in v1
 and the first one begins at position 3.
There is a sequence of elements in v1 that are equivalent
 to those in v2 under the binary predicate twice
 and the first one begins at position 2.

Requirements

Header: <algorithm>

Namespace: std

See Also

Reference

Standard Template Library