find_first_of


Category: algorithms	Component type: function

Prototype

find_first_of is an overloaded name; there are actually two find_first_of functions.

template <class InputIterator
class ForwardIterator>
InputIterator find_first_of(InputIterator first1
InputIterator last1

                            ForwardIterator first2
ForwardIterator last2);

template <class InputIterator
class ForwardIterator
class BinaryPredicate>
InputIterator find_first_of(InputIterator first1
InputIterator last1

                            ForwardIterator first2
ForwardIterator last2

                            BinaryPredicate comp);

Description

Find_first_of is similar to find in that it performs linear seach 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. Specifically find_first_of searches for the first occurrance in the range [first1 last1) of any of the elements in [first2 last2). (Note that this behavior is reminiscent of the function strpbrk from the standard C library.)

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. 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.

Definition

Defined in the standard header algorithm and in the nonstandard backward-compatibility header algo.h.

Requirements on types

For the first version:

InputIterator is a model of Input Iterator.
ForwardIterator is a model of Forward Iterator.
InputIterator's value type is EqualityComparable and can be compared for equality with ForwardIterator's value type.

For the second version:

InputIterator is a model of Input Iterator.
ForwardIterator is a model of Forward Iterator.
BinaryPredicate is a model of Binary Predicate.
InputIterator's value type is convertible to BinaryPredicate's first argument type.
ForwardIterator's value type is convertible to BinaryPredicate's second argument type.

Preconditions

[first1 last1) is a valid range.
[first2 last2) is a valid range.

Complexity

At most (last1 - first1) * (last2 - first2) comparisons.

Example

Like strpbrk one use for find_first_of is finding whitespace in a string; space tab and newline are all whitespace characters.

int main()
{
  const char* WS = "\t\n ";
  const int n_WS = strlen(WS);

  char* s1 = "This sentence contains five words.";
  char* s2 = "OneWord";


  char* end1 = find_first_of(s1
s1 + strlen(s1)

                             WS
WS + n_WS);
  char* end2 = find_first_of(s2
s2 + strlen(s2)

                             WS
WS + n_WS);

  printf("First word of s1: %.*s\n"
end1 - s1
s1);
  printf("First word of s2: %.*s\n"
end2 - s2
s2);
}