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std::stable_sort

From cppreference.com
< cpp‎ | algorithm
 
 
Algorithm library
Execution policies (C++17)
Non-modifying sequence operations
(C++11)(C++11)(C++11)
(C++17)
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
(C++11)
stable_sort
Binary search operations
Set operations (on sorted ranges)
Heap operations
(C++11)
Minimum/maximum operations
(C++11)
(C++17)

Permutations
Numeric operations
C library
 
Defined in header <algorithm>
template< class RandomIt >
void stable_sort( RandomIt first, RandomIt last );
(1)
template< class ExecutionPolicy, class RandomIt >
void stable_sort( ExecutionPolicy&& policy, RandomIt first, RandomIt last );
(2) (since C++17)
template< class RandomIt, class Compare >
void stable_sort( RandomIt first, RandomIt last, Compare comp );
(3)
template< class ExecutionPolicy, class RandomIt, class Compare >
void stable_sort( ExecutionPolicy&& policy, RandomIt first, RandomIt last, Compare comp );
(4) (since C++17)

Sorts the elements in the range [first, last) in ascending order. The order of equal elements is guaranteed to be preserved.

1) Elements are compared using operator<.
3) Elements are compared using the given comparison function comp.
2,4) Same as (1,3), but executed according to policy. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

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);

The signature does not need to have const &, but the function object must not modify the objects passed to it.
The types Type1 and Type2 must be such that an object of type RandomIt can be dereferenced and then implicitly converted to both of them. ​

Type requirements
-
RandomIt must meet the requirements of ValueSwappable and RandomAccessIterator.
-
The type of dereferenced RandomIt must meet the requirements of MoveAssignable and MoveConstructible.

[edit] Return value

(none)

[edit] Complexity

O(N·log2(N)), where N = std::distance(first, last) applications of cmp. If additional memory is available, then the complexity is O(N·log(N)).

[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 three standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
  • If the algorithm fails to allocate memory, std::bad_alloc is thrown.

[edit] Notes

This function attempts to allocate a temporary buffer equal in size to the sequence to be sorted, typically by calling std::get_temporary_buffer. If the allocation fails, the less efficient algorithm is chosen.

[edit] Example

#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
 
struct Employee {
    Employee(int age, std::string name) : age(age), name(name) { } 
    int age;
    std::string name;  // Does not particpate in comparisons
};
 
bool operator<(const Employee &lhs, const Employee &rhs) {
    return lhs.age < rhs.age;
}
 
int main()
{
    std::vector<Employee> v = { 
        Employee(108, "Zaphod"),
        Employee(32, "Arthur"),
        Employee(108, "Ford"),
    };  
 
    std::stable_sort(v.begin(), v.end());
 
    for (const Employee &e : v) {
        std::cout << e.age << ", " << e.name << '\n';
    }   
}

Output:

32, Arthur
108, Zaphod
108, Ford

[edit] See also

sorts the first N elements of a range
(function template) [edit]
sorts a range into ascending order
(function template) [edit]
parallelized version of std::stable_sort
(function template) [edit]