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std::all_of, std::any_of, std::none_of

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< cpp‎ | algorithm
Revision as of 01:35, 10 October 2013 by Newacct (Talk | contribs)

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Defined in header <algorithm>
template< class InputIt, class UnaryPredicate >
bool all_of( InputIt first, InputIt last, UnaryPredicate p );
(1) (since C++11)
template< class InputIt, class UnaryPredicate >
bool any_of( InputIt first, InputIt last, UnaryPredicate p );
(2) (since C++11)
template< class InputIt, class UnaryPredicate >
bool none_of( InputIt first, InputIt last, UnaryPredicate p );
(3) (since C++11)
1) Checks if unary predicate p returns true for all elements in the range [first, last).
2) Checks if unary predicate p returns true for at least one element in the range [first, last).
3) Checks if unary predicate p returns true for no elements in the range [first, last).

Contents

[edit] Parameters

first, last - the range of elements to examine
p - unary predicate .

The signature of the predicate function should be equivalent to the following:

 bool pred(const Type &a);

The signature does not need to have const &, but the function must not modify the objects passed to it.
The type Type must be such that an object of type InputIt can be dereferenced and then implicitly converted to Type. ​

Type requirements
-
InputIt must meet the requirements of InputIterator.
-
UnaryPredicate must meet the requirements of Predicate.

[edit] Return value

1) true if unary predicate returns true for all elements in the range, false otherwise. Returns true if the range is empty.
2) true if unary predicate returns true for at least one element in the range, false otherwise. Returns false if the range is empty.
3) true if unary predicate returns true for no elements in the range, false otherwise. Returns true if the range is empty.

[edit] Complexity

At most last - first applications of the predicate

[edit] Possible implementation

First version
template< class InputIt, class UnaryPredicate >
bool all_of(InputIt first, InputIt last, UnaryPredicate p)
{
    return std::find_if_not(first, last, p) == last;
}
Second version
template< class InputIt, class UnaryPredicate >
bool any_of(InputIt first, InputIt last, UnaryPredicate p)
{
    return std::find_if(first, last, p) != last;
}
Third version
template< class InputIt, class UnaryPredicate >
bool none_of(InputIt first, InputIt last, UnaryPredicate p)
{
    return std::find_if(first, last, p) == last;
}

[edit] Example

#include <vector>
#include <numeric>
#include <algorithm>
#include <iterator>
#include <iostream>
#include <functional>
 
int main()
{
    std::vector<int> v(10, 2);
    std::partial_sum(v.cbegin(), v.cend(), v.begin());
    std::cout << "Among the numbers: ";
    std::copy(v.cbegin(), v.cend(), std::ostream_iterator<int>(std::cout, " "));
    std::cout << '\n';
 
    if (std::all_of(v.cbegin(), v.cend(), [](int i){ return i % 2 == 0; })) {
        std::cout << "All numbers are even\n";
    }
    if (std::none_of(v.cbegin(), v.cend(), std::bind(std::modulus<int>(), 
                                                     std::placeholders::_1, 2))) {
        std::cout << "None of them are odd\n";
    }
    struct DivisibleBy
    {
        const int d;
        DivisibleBy(int n) : d(n) {}
        bool operator()(int n) const { return n % d == 0; }
    };
 
    if (std::any_of(v.cbegin(), v.cend(), DivisibleBy(7))) {
        std::cout << "At least one number is divisible by 7\n";
    }
}

Output:

Among the numbers: 2 4 6 8 10 12 14 16 18 20 
All numbers are even
None of them are odd
At least one number is divisible by 7