std::sort
Defined in header <algorithm>
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template< class RandomIt > void sort( RandomIt first, RandomIt last ); |
(1) | (constexpr since C++20) |
template< class ExecutionPolicy, class RandomIt > void sort( ExecutionPolicy&& policy, |
(2) | (since C++17) |
template< class RandomIt, class Compare > void sort( RandomIt first, RandomIt last, Compare comp ); |
(3) | (constexpr since C++20) |
template< class ExecutionPolicy, class RandomIt, class Compare > void sort( ExecutionPolicy&& policy, |
(4) | (since C++17) |
Sorts the elements in the range [
first,
last)
in non-descending order. The order of equal elements is not guaranteed to be preserved.
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true. |
(until C++20) |
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. |
(since C++20) |
If any of the following conditions is satisfied, the behavior is undefined:
|
(until C++11) |
|
(since C++11) |
Contents |
[edit] Parameters
first, last | - | the range of elements to sort |
policy | - | the execution policy to use. See execution policy for details. |
comp | - | comparison function object (i.e. an object that satisfies the requirements of Compare) which returns true if the first argument is less than (i.e. is ordered before) the second. The signature of the comparison function should be equivalent to the following: bool cmp(const Type1& a, const Type2& b); While the signature does not need to have const&, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) |
Type requirements | ||
-RandomIt must meet the requirements of LegacyRandomAccessIterator.
| ||
-Compare must meet the requirements of Compare.
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[edit] Complexity
Given N as last - first:
[edit] Exceptions
The overloads with a template parameter named ExecutionPolicy
report errors as follows:
- If execution of a function invoked as part of the algorithm throws an exception and
ExecutionPolicy
is one of the standard policies, std::terminate is called. For any otherExecutionPolicy
, the behavior is implementation-defined. - If the algorithm fails to allocate memory, std::bad_alloc is thrown.
[edit] Possible implementation
See also the implementations in libstdc++ and libc++.
[edit] Notes
Before LWG713, the complexity requirement allowed sort()
to be implemented using only Quicksort, which may need O(N2
) comparisons in the worst case.
Introsort can handle all cases with O(N·log(N)) comparisons (without incurring additional overhead in the average case), and thus is usually used for implementing sort()
.
libc++ has not implemented the corrected time complexity requirement until LLVM 14.
[edit] Example
#include <algorithm> #include <array> #include <functional> #include <iostream> #include <string_view> int main() { std::array<int, 10> s{5, 7, 4, 2, 8, 6, 1, 9, 0, 3}; auto print = [&s](std::string_view const rem) { for (auto a : s) std::cout << a << ' '; std::cout << ": " << rem << '\n'; }; std::sort(s.begin(), s.end()); print("sorted with the default operator<"); std::sort(s.begin(), s.end(), std::greater<int>()); print("sorted with the standard library compare function object"); struct { bool operator()(int a, int b) const { return a < b; } } customLess; std::sort(s.begin(), s.end(), customLess); print("sorted with a custom function object"); std::sort(s.begin(), s.end(), [](int a, int b) { return a > b; }); print("sorted with a lambda expression"); }
Output:
0 1 2 3 4 5 6 7 8 9 : sorted with the default operator< 9 8 7 6 5 4 3 2 1 0 : sorted with the standard library compare function object 0 1 2 3 4 5 6 7 8 9 : sorted with a custom function object 9 8 7 6 5 4 3 2 1 0 : sorted with a lambda expression
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR | Applied to | Behavior as published | Correct behavior |
---|---|---|---|
LWG 713 | C++98 | the O(N·log(N)) time complexity was only required on the average | it is required for the worst case |
[edit] See also
sorts the first N elements of a range (function template) | |
sorts a range of elements while preserving order between equal elements (function template) | |
(C++20) |
sorts a range into ascending order (niebloid) |