Книга: Standard Template Library Programmer

find_first_of

find_first_of

Category: algorithms

Component type: function

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);

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.

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

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.

• [first1, last1) is a valid range.

• [first2, last2) is a valid range.

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

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 = "tn ";
 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: %.*sn", end1 – s1, s1);
 printf("First word of s2: %.*sn", end2 – s2, s2);
}

find, find_if, search

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