function template
<algorithm>
std::is_partitioned
template <class InputIterator, class UnaryPredicate>
bool is_partitioned (InputIterator first, InputIterator last, UnaryPredicate pred);
Test whether range is partitioned
Returns true
if all the elements in the range [first,last)
for which pred returns true
precede those for which it returns false
.
If the range is empty, the function returns true
.
The behavior of this function template is equivalent to:
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template <class InputIterator, class UnaryPredicate>
bool is_partitioned (InputIterator first, InputIterator last, UnaryPredicate pred)
{
while (first!=last && pred(*first)) {
++first;
}
while (first!=last) {
if (pred(*first)) return false;
++first;
}
return true;
}
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Parameters
- first, last
- Input iterators to the initial and final positions of the sequence. The range used is
[first,last)
, which contains all the elements between first and last, including the element pointed by first but not the element pointed by last.
- pred
- Unary function that accepts an element in the range as argument, and returns a value convertible to
bool
. The value returned indicates whether the element belongs to the first group (if true
, the element is expected before all the elements for which it returns false
).
The function shall not modify its argument.
This can either be a function pointer or a function object.
Return value
true
if all the elements in the range [first,last)
for which pred returns true
precede those for which it returns false
.
Otherwise it returns false
.
If the range is empty, the function returns true
.
Example
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// is_partitioned example
#include <iostream> // std::cout
#include <algorithm> // std::is_partitioned
#include <array> // std::array
bool IsOdd (int i) { return (i%2)==1; }
int main () {
std::array<int,7> foo {1,2,3,4,5,6,7};
// print contents:
std::cout << "foo:"; for (int& x:foo) std::cout << ' ' << x;
if ( std::is_partitioned(foo.begin(),foo.end(),IsOdd) )
std::cout << " (partitioned)\n";
else
std::cout << " (not partitioned)\n";
// partition array:
std::partition (foo.begin(),foo.end(),IsOdd);
// print contents again:
std::cout << "foo:"; for (int& x:foo) std::cout << ' ' << x;
if ( std::is_partitioned(foo.begin(),foo.end(),IsOdd) )
std::cout << " (partitioned)\n";
else
std::cout << " (not partitioned)\n";
return 0;
}
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Possible output:
foo: 1 2 3 4 5 6 7 (not partitioned)
foo: 1 7 3 5 4 6 2 (partitioned)
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Complexity
Up to linear in the distance between first and last: Calls pred for each element until a mismatch is found.
Data races
Some (or all) of the objects in the range [first,last)
are accessed (once at most).
Exceptions
Throws if either pred or an operation on an iterator throws.
Note that invalid parameters cause undefined behavior.