...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
The header file 'boost/algorithm/cxx11/none_of.hpp' contains four variants
of a single algorithm, none_of
.
The algorithm tests all the elements of a sequence and returns true if they
none of them share a property.
The routine none_of
takes
a sequence and a predicate. It will return true if the predicate returns
false when applied to every element in the sequence.
The routine none_of_equal
takes a sequence and a value. It will return true if none of the elements
in the sequence compare equal to the passed in value.
Both routines come in two forms; the first one takes two iterators to define the range. The second form takes a single range parameter, and uses Boost.Range to traverse it.
The function none_of
returns
true if the predicate returns false for every item in the sequence. There
are two versions; one takes two iterators, and the other takes a range.
namespace boost { namespace algorithm { template<typename InputIterator, typename Predicate> bool none_of ( InputIterator first, InputIterator last, Predicate p ); template<typename Range, typename Predicate> bool none_of ( const Range &r, Predicate p ); }}
The function none_of_equal
is similar to none_of
, but
instead of taking a predicate to test the elements of the sequence, it takes
a value to compare against.
namespace boost { namespace algorithm { template<typename InputIterator, typename V> bool none_of_equal ( InputIterator first, InputIterator last, V const &val ); template<typename Range, typename V> bool none_of_equal ( const Range &r, V const &val ); }}
Given the container c
containing
{ 0, 1,
2, 3, 14, 15 }
,
then
bool isOdd ( int i ) { return i % 2 == 1; } bool lessThan10 ( int i ) { return i < 10; } using boost::algorithm; none_of ( c, isOdd ) --> false none_of ( c.begin (), c.end (), lessThan10 ) --> false none_of ( c.begin () + 4, c.end (), lessThan10 ) --> true none_of ( c.end (), c.end (), isOdd ) --> true // empty range none_of_equal ( c, 3 ) --> false none_of_equal ( c.begin (), c.begin () + 3, 3 ) --> true none_of_equal ( c.begin (), c.begin (), 99 ) --> true // empty range
none_of
and none_of_equal
work on all iterators except
output iterators.
All of the variants of none_of
and none_of_equal
run in
O(N) (linear) time; that is, they compare against each
element in the list once. If any of the comparisons succeed, the algorithm
will terminate immediately, without examining the remaining members of the
sequence.
All of the variants of none_of
and none_of_equal
take their
parameters by value or const reference, and do not depend upon any global
state. Therefore, all the routines in this file provide the strong exception
guarantee.
none_of
is
also available as part of the C++11 standard.
none_of
and none_of_equal
both return true for
empty ranges, no matter what is passed to test against.
none_of_value
is a template parameter, rather than deduced from the first parameter
(std::iterator_traits<InputIterator>::value_type
) because that allows more
flexibility for callers, and takes advantage of built-in comparisons
for the type that is pointed to by the iterator. The function is defined
to return true if, for all elements in the sequence, the expression
*iter
== val
evaluates to false (where iter
is an iterator to each element in the sequence)