find_first_of
Searches the first of several possible elements
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Definition
The find_first_of() algorithm is defined in the standard header <algorithm> and in the nonstandard backward-compatibility header <algo.h>.
Interface
#include <algorithm>
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:
| Parameter | Description |
| 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 |
Description
Find_first_of is similar to find, in that it performs linear search through a range of Input Iterators. The difference is that while find searches for one particular value, find_first_of searches for any of several values.
The two versions of find_first_of differ in how they compare elements for equality.
The first uses operator== and the second uses and arbitrary user-supplied function object comp.
Return Value
The first version returns the first iterator i in [first1, last1) such that, for some iterator j in [first2, last2), *i == *j.
The second returns the first iterator i in [first1, last1) such that, for some iterator j in [first2, last2), comp(*i, *j) is true. As usual, both versions return last1 if no such iterator i exists.
Complexity
At most, performs distance1*distance2 comparisons or applications of comp (where distanceX is the distance between firstX and lastX).
References
Example 1
This program illustrates the use of the STL find_first_of() algorithm (default version) to find the first occurrence of any one of a range of integer values in a vector within another range of integer values, also in a vector.
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main()
{
int a1[] = {1, 2, 333, 3, 4, 5, 6, 444, 7, 8, 9, 10};
vector<int> v1(a1, a1+12);
cout <<"\nHere are the contents of v1:\n";
for (vector<int>::size_type i=0; i<v1.size(); i++)
cout <<v1.at(i)<<" ";
int a2[] = {333, 444, 555};
vector<int> v2(a2, a2+3);
cout <<"\nHere are the contents of v2:\n";
for (vector<int>::size_type i=0; i<v2.size(); i++)
cout <<v2.at(i)<<" ";
vector<int>::iterator p;
p = find_first_of(v1.begin(), v1.end(), v2.begin(), v2.end());
if (p != v1.end())
cout <<"\nThe first instance of a value from v2 occurring in v1 happens at location "
<<(int)(p-v1.begin()+1)<<".";
else
cout <<"\nNo instance of v2 was found in v1.";
p = find_first_of(p+1, v1.end(), v2.begin(), v2.end());
if (p != v1.end())
cout <<"\nThe next instance of a value from v2 occurring in v1 happens at location "
<<(int)(p-v1.begin()+1) << ".";
else
cout <<"\nNo further instance of a value from v2 occurring in v1 was found.";
p = find_first_of(p+1, v1.end(), v2.begin(), v2.end());
if (p != v1.end())
cout <<"\nThe next instance of a value from v2 occurring in v1 happens at location "
<<(int)(p-v1.begin()+1)<<".";
else
cout <<"\nNo further instance of a value from v2 occurring in v1 was found.";
return 0;
}Output:
Here are the contents of v1:
1 2 333 3 4 5 6 444 7 8 9 10
Here are the contents of v2:
333 444 555
The first instance of a value from v2 occurring in v1 happens at location 3.
The next instance of a value from v2 occurring in v1 happens at location 8.
No further instance of a value from v2 occurring in v1 was found.