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 = '
';
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
', end1 – s1, s1);
printf('First word of s2: %.*s
', end2 – s2, s2);
}
See also find, find_if, search
Category: algorithms
Component type: function
Prototype Count is an overloaded name: there are two count functions.
template <class InputIterator, class EqualityComparable>
iterator_traits<InputIterator>::difference_type count (InputIterator first, InputIterator last, const EqualityComparable& value);
template <class InputIterator, class EqualityComparable, class Size>
void count(InputIterator first, InputIterator last, const EqualityComparable& value, Size& n);
Description Count finds the number of elements in [first, last) that are equal to value. More precisely, the first version of count returns the number of iterators i in [first, last) such that *i == value. The second version of count adds to n the number of iterators i in [first, last) such that *i == value.
The second version of count was the one defined in the original STL, and the first version is the one defined in the draft C++ standard; the definition was changed because the older interface was clumsy and error-prone. The older interface required the use of a temporary variable, which had to be initialized to 0 before the call to count.
Both interfaces are currently supported [1], for reasons of backward compatibility, but eventually the older version will be removed.
Definition Defined in the standard header algorithm, and in the nonstandard backward-compatibility header algo.h.
Requirements on types For the first version, which takes three arguments:
• InputIterator is a model of Input Iterator.
• EqualityComparable is a model of Equality Comparable.
• InputIterator's value type is a model of Equality Comparable.
• An object of InputIterator's value type can be compared for equality with an object of type EqualityComparable.
For the second version, which takes four arguments:
• InputIterator is a model of Input Iterator.
• EqualityComparable is a model of Equality Comparable.
• Size is an integral type that can hold values of InputIterator's distance type.
• InputIterator's value type is a model of Equality Comparable.
• An object of InputIterator's value type can be compared for equality with an object of type EqualityComparable.
Preconditions 
