Algorithms library

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C++
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
(C++11)
(C++11)
(C++11)
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
(C++11)
(C++17)
Lexicographical comparison operations
(C++20)
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
 

The algorithms library defines functions for a variety of purposes (e.g. searching, sorting, counting, manipulating) that operate on ranges of elements. Note that a range is defined as [first, last) where last refers to the element past the last element to inspect or modify.

Constrained algorithms

C++20 provides constrained versions of most algorithms in the namespace std::ranges. In these algorithms, a range can be specified as either an iterator-sentinel pair or as a single range argument, and projections and pointer-to-member callables are supported. Additionally, the return types of most algorithms have been changed to return all potentially useful information computed during the execution of the algorithm. 

std::vector<int> v {7, 1, 4, 0, -1};
std::ranges::sort(v); // constrained algorithm
 (since C++20)


Execution policies

Most algorithms have overloads that accept execution policies. The standard library algorithms support several execution policies, and the library provides corresponding execution policy types and objects. Users may select an execution policy statically by invoking a parallel algorithm with an execution policy object of the corresponding type.

Standard library implementations (but not the users) may define additional execution policies as an extension. The semantics of parallel algorithms invoked with an execution policy object of implementation-defined type is implementation-defined.

Parallel version of algorithms (except for std::for_each and std::for_each_n) are allowed to make arbitrary copies of elements from ranges, as long as both std::is_trivially_copy_constructible_v<T> and std::is_trivially_destructible_v<T> are true, where T is the type of elements.

Defined in header <execution>
Defined in namespace std::execution
(C++17)(C++17)(C++17)(C++20)
 execution policy types
(class)
(C++17)(C++17)(C++17)(C++20)
 global execution policy objects
(constant)
Defined in namespace std
(C++17)
 test whether a class represents an execution policy
(class template)
Feature-test macro Value Std Feature
__cpp_lib_parallel_algorithm 201603L (C++17) Parallel algorithms
__cpp_lib_execution 201603L (C++17) Execution policies
201902L (C++20) std::execution::unsequenced_policy
(since C++17)

Non-modifying sequence operations

Batch operations

Defined in header <algorithm>
applies a function to a range of elements
(function template)
(C++20)
 applies a function to a range of elements
(niebloid)
(C++17)
 applies a function object to the first N elements of a sequence
(function template)
(C++20)
 applies a function object to the first N elements of a sequence
(niebloid)

Search operations

Defined in header <algorithm>
(C++11)(C++11)(C++11)
 checks if a predicate is true for all, any or none of the elements in a range
(function template)
(C++20)(C++20)(C++20)
 checks if a predicate is true for all, any or none of the elements in a range
(niebloid)
(C++23)(C++23)
 checks if the range contains the given element or subrange
(niebloid)
(C++11)
 finds the first element satisfying specific criteria
(function template)
(C++20)(C++20)(C++20)
 finds the first element satisfying specific criteria
(niebloid)
(C++23)(C++23)(C++23)
 finds the last element satisfying specific criteria
(niebloid)
 finds the last sequence of elements in a certain range
(function template)
(C++20)
 finds the last sequence of elements in a certain range
(niebloid)
 searches for any one of a set of elements
(function template)
(C++20)
 searches for any one of a set of elements
(niebloid)
 finds the first two adjacent items that are equal (or satisfy a given predicate)
(function template)
(C++20)
 finds the first two adjacent items that are equal (or satisfy a given predicate)
(niebloid)
 returns the number of elements satisfying specific criteria
(function template)
(C++20)(C++20)
 returns the number of elements satisfying specific criteria
(niebloid)
 finds the first position where two ranges differ
(function template)
(C++20)
 finds the first position where two ranges differ
(niebloid)
 determines if two sets of elements are the same
(function template)
(C++20)
 determines if two sets of elements are the same
(niebloid)
 searches for the first occurrence of a range of elements
(function template)
(C++20)
 searches for the first occurrence of a range of elements
(niebloid)
 searches for the first occurrence of a number consecutive copies of an element in a range
(function template)
(C++20)
 searches for the first occurrence of a number consecutive copies of an element in a range
(niebloid)
(C++23)
 checks whether a range starts with another range
(niebloid)
(C++23)
 checks whether a range ends with another range
(niebloid)

Fold operations

Defined in header <algorithm>
(C++23)
 left-folds a range of elements
(niebloid)
(C++23)
 left-folds a range of elements using the first element as an initial value
(niebloid)
(C++23)
 right-folds a range of elements
(niebloid)
(C++23)
 right-folds a range of elements using the last element as an initial value
(niebloid)
(C++23)
 left-folds a range of elements, and returns a pair (iterator, value)
(niebloid)
(C++23)
 left-folds a range of elements using the first element as an initial value, and returns a pair (iterator, optional)
(niebloid)

Modifying sequence operations

Copy operations

Defined in header <algorithm>
(C++11)
 copies a range of elements to a new location
(function template)
(C++20)(C++20)
 copies a range of elements to a new location
(niebloid)
(C++11)
 copies a number of elements to a new location
(function template)
(C++20)
 copies a number of elements to a new location
(niebloid)
 copies a range of elements in backwards order
(function template)
(C++20)
 copies a range of elements in backwards order
(niebloid)
(C++11)
 moves a range of elements to a new location
(function template)
(C++20)
 moves a range of elements to a new location
(niebloid)
(C++11)
 moves a range of elements to a new location in backwards order
(function template)
(C++20)
 moves a range of elements to a new location in backwards order
(niebloid)

Swap operations

Defined in header <algorithm>   (until C++11)
Defined in header <utility>     (since C++11)
Defined in header <string_view>
swaps the values of two objects
(function template)
Defined in header <algorithm>
swaps two ranges of elements
(function template)
(C++20)
 swaps two ranges of elements
(niebloid)
 swaps the elements pointed to by two iterators
(function template)

Transformation operations

Defined in header <algorithm>
applies a function to a range of elements, storing results in a destination range
(function template)
(C++20)
 applies a function to a range of elements
(niebloid)
 replaces all values satisfying specific criteria with another value
(function template)
(C++20)(C++20)
 replaces all values satisfying specific criteria with another value
(niebloid)
 copies a range, replacing elements satisfying specific criteria with another value
(function template)
(C++20)(C++20)
 copies a range, replacing elements satisfying specific criteria with another value
(niebloid)

Generation operations

Defined in header <algorithm>
copy-assigns the given value to every element in a range
(function template)
(C++20)
 assigns a range of elements a certain value
(niebloid)
 copy-assigns the given value to N elements in a range
(function template)
(C++20)
 assigns a value to a number of elements
(niebloid)
 assigns the results of successive function calls to every element in a range
(function template)
(C++20)
 saves the result of a function in a range
(niebloid)
 assigns the results of successive function calls to N elements in a range
(function template)
(C++20)
 saves the result of N applications of a function
(niebloid)

Removing operations

Defined in header <algorithm>
removes elements satisfying specific criteria
(function template)
(C++20)(C++20)
 removes elements satisfying specific criteria
(niebloid)
 copies a range of elements omitting those that satisfy specific criteria
(function template)
(C++20)(C++20)
 copies a range of elements omitting those that satisfy specific criteria
(niebloid)
 removes consecutive duplicate elements in a range
(function template)
(C++20)
 removes consecutive duplicate elements in a range
(niebloid)
 creates a copy of some range of elements that contains no consecutive duplicates
(function template)
(C++20)
 creates a copy of some range of elements that contains no consecutive duplicates
(niebloid)

Order-changing operations

Defined in header <algorithm>
reverses the order of elements in a range
(function template)
(C++20)
 reverses the order of elements in a range
(niebloid)
 creates a copy of a range that is reversed
(function template)
(C++20)
 creates a copy of a range that is reversed
(niebloid)
 rotates the order of elements in a range
(function template)
(C++20)
 rotates the order of elements in a range
(niebloid)
 copies and rotate a range of elements
(function template)
(C++20)
 copies and rotate a range of elements
(niebloid)
(C++20)
 shifts elements in a range
(function template)
(until C++17)(C++11)
 randomly re-orders elements in a range
(function template)
(C++20)
 randomly re-orders elements in a range
(niebloid)
(C++23)
 shifts elements in a range
(niebloid)

Sampling operations

Defined in header <algorithm>
(C++17)
 selects N random elements from a sequence
(function template)
(C++20)
 selects N random elements from a sequence
(niebloid)

Sorting and related operations

Requirements

Some algorithms require the sequence represented by the arguments to be “sorted” or “partitioned”. The behavior is undefined if the requirement is not met.

A sequence is sorted with respect to a comparator comp if for every iterator iter pointing to the sequence and every non-negative integer n such that iter + n[1] is a valid iterator pointing to an element of the sequence, comp(*(iter + n), *iter) == false[1].

(until C++20)

A sequence is sorted with respect to comp and proj for a comparator comp and projection proj if for every iterator iter pointing to the sequence and every non-negative integer n such that iter + n[1] is a valid iterator pointing to an element of the sequence, bool(std::invoke(comp, std::invoke(proj, *(iter + n)),
                       std::invoke(proj, *iter)))[1] is false.

A sequence is sorted with respect to a comparator comp if the sequence is sorted with respect to comp and std::identity{} (the identity projection).

(since C++20)

A sequence [start, finish) is partitioned with respect to an expression f(e) if there exists an integer n such that for all i in [​0​, std::distance(start, finish)), f(*(start + i))[1] is true if and only if i < n.

  1. ↑ 1.0 1.1 1.2 1.3 1.4 iter + n simply means “the result of iter being incremented n times”, regardless of whether iter is a random access iterator.

Partitioning operations

Defined in header <algorithm>
(C++11)
 determines if the range is partitioned by the given predicate
(function template)
(C++20)
 determines if the range is partitioned by the given predicate
(niebloid)
 divides a range of elements into two groups
(function template)
(C++20)
 divides a range of elements into two groups
(niebloid)
(C++11)
 copies a range dividing the elements into two groups
(function template)
(C++20)
 copies a range dividing the elements into two groups
(niebloid)
 divides elements into two groups while preserving their relative order
(function template)
(C++20)
 divides elements into two groups while preserving their relative order
(niebloid)
(C++11)
 locates the partition point of a partitioned range
(function template)
(C++20)
 locates the partition point of a partitioned range
(niebloid)

Sorting operations

Defined in header <algorithm>
sorts a range into ascending order
(function template)
(C++20)
 sorts a range into ascending order
(niebloid)
 sorts a range of elements while preserving order between equal elements
(function template)
(C++20)
 sorts a range of elements while preserving order between equal elements
(niebloid)
 sorts the first N elements of a range
(function template)
(C++20)
 sorts the first N elements of a range
(niebloid)
 copies and partially sorts a range of elements
(function template)
(C++20)
 copies and partially sorts a range of elements
(niebloid)
(C++11)
 checks whether a range is sorted into ascending order
(function template)
(C++20)
 checks whether a range is sorted into ascending order
(niebloid)
(C++11)
 finds the largest sorted subrange
(function template)
(C++20)
 finds the largest sorted subrange
(niebloid)
 partially sorts the given range making sure that it is partitioned by the given element
(function template)
(C++20)
 partially sorts the given range making sure that it is partitioned by the given element
(niebloid)

Binary search operations (on partitioned ranges)

Defined in header <algorithm>
returns an iterator to the first element not less than the given value
(function template)
(C++20)
 returns an iterator to the first element not less than the given value
(niebloid)
 returns an iterator to the first element greater than a certain value
(function template)
(C++20)
 returns an iterator to the first element greater than a certain value
(niebloid)
 returns range of elements matching a specific key
(function template)
(C++20)
 returns range of elements matching a specific key
(niebloid)
 determines if an element exists in a partially-ordered range
(function template)
(C++20)
 determines if an element exists in a partially-ordered range
(niebloid)

Set operations (on sorted ranges)

Defined in header <algorithm>
returns true if one sequence is a subsequence of another
(function template)
(C++20)
 returns true if one sequence is a subsequence of another
(niebloid)
 computes the union of two sets
(function template)
(C++20)
 computes the union of two sets
(niebloid)
 computes the intersection of two sets
(function template)
(C++20)
 computes the intersection of two sets
(niebloid)
 computes the difference between two sets
(function template)
(C++20)
 computes the difference between two sets
(niebloid)
 computes the symmetric difference between two sets
(function template)
(C++20)
 computes the symmetric difference between two sets
(niebloid)

Merge operations (on sorted ranges)

Defined in header <algorithm>
merges two sorted ranges
(function template)
(C++20)
 merges two sorted ranges
(niebloid)
 merges two ordered ranges in-place
(function template)
(C++20)
 merges two ordered ranges in-place
(niebloid)

Heap operations

A random access range [first, last) is a heap with respect to a comparator comp if bool(comp(first[(i - 1) / 2], first[i])) is false for all integer i in (​0​, last - first).

(until C++20)

A random access range [first, last) is a heap with respect to comp and proj for a comparator comp and projection proj if bool(std::invoke(comp, std::invoke(proj, first[(i - 1) / 2]),
                       std::invoke(proj, first[i])) is false for all integer i in (​0​, last - first).

A random access range [first, last) is a heap with respect to a comparator comp if the range is a heap with respect to comp and std::identity{} (the identity projection).

(since C++20)

A heap can be created by std::make_heap and ranges::make_heap(since C++20).

For more properties of heap, see max heap.


Defined in header <algorithm>
adds an element to a max heap
(function template)
(C++20)
 adds an element to a max heap
(niebloid)
 removes the largest element from a max heap
(function template)
(C++20)
 removes the largest element from a max heap
(niebloid)
 creates a max heap out of a range of elements
(function template)
(C++20)
 creates a max heap out of a range of elements
(niebloid)
 turns a max heap into a range of elements sorted in ascending order
(function template)
(C++20)
 turns a max heap into a range of elements sorted in ascending order
(niebloid)
(C++11)
 checks if the given range is a max heap
(function template)
(C++20)
 checks if the given range is a max heap
(niebloid)
(C++11)
 finds the largest subrange that is a max heap
(function template)
(C++20)
 finds the largest subrange that is a max heap
(niebloid)

Minimum/maximum operations

Defined in header <algorithm>
returns the greater of the given values
(function template)
(C++20)
 returns the greater of the given values
(niebloid)
 returns the largest element in a range
(function template)
(C++20)
 returns the largest element in a range
(niebloid)
 returns the smaller of the given values
(function template)
(C++20)
 returns the smaller of the given values
(niebloid)
 returns the smallest element in a range
(function template)
(C++20)
 returns the smallest element in a range
(niebloid)
(C++11)
 returns the smaller and larger of two elements
(function template)
(C++20)
 returns the smaller and larger of two elements
(niebloid)
(C++11)
 returns the smallest and the largest elements in a range
(function template)
(C++20)
 returns the smallest and the largest elements in a range
(niebloid)
(C++17)
 clamps a value between a pair of boundary values
(function template)
(C++20)
 clamps a value between a pair of boundary values
(niebloid)

Lexicographical comparison operations

Defined in header <algorithm>
returns true if one range is lexicographically less than another
(function template)
(C++20)
 returns true if one range is lexicographically less than another
(niebloid)
(C++20)
 compares two ranges using three-way comparison
(function template)

Permutation operations

Defined in header <algorithm>
generates the next greater lexicographic permutation of a range of elements
(function template)
(C++20)
 generates the next greater lexicographic permutation of a range of elements
(niebloid)
 generates the next smaller lexicographic permutation of a range of elements
(function template)
(C++20)
 generates the next smaller lexicographic permutation of a range of elements
(niebloid)
(C++11)
 determines if a sequence is a permutation of another sequence
(function template)
(C++20)
 determines if a sequence is a permutation of another sequence
(niebloid)

Numeric operations

Defined in header <numeric>
(C++11)
 fills a range with successive increments of the starting value
(function template)
(C++23)
 fills a range with successive increments of the starting value
(niebloid)
 sums up or folds a range of elements
(function template)
computes the inner product of two ranges of elements
(function template)
computes the differences between adjacent elements in a range
(function template)
computes the partial sum of a range of elements
(function template)
(C++17)
 similar to std::accumulate, except out of order
(function template)
(C++17)
 similar to std::partial_sum, excludes the ith input element from the ith sum
(function template)
(C++17)
 similar to std::partial_sum, includes the ith input element in the ith sum
(function template)
(C++17)
 applies an invocable, then reduces out of order
(function template)
(C++17)
 applies an invocable, then calculates exclusive scan
(function template)
(C++17)
 applies an invocable, then calculates inclusive scan
(function template)

Operations on uninitialized memory

Defined in header <memory>
copies a range of objects to an uninitialized area of memory
(function template)
(C++20)
 copies a range of objects to an uninitialized area of memory
(niebloid)
(C++11)
 copies a number of objects to an uninitialized area of memory
(function template)
(C++20)
 copies a number of objects to an uninitialized area of memory
(niebloid)
 copies an object to an uninitialized area of memory, defined by a range
(function template)
(C++20)
 copies an object to an uninitialized area of memory, defined by a range
(niebloid)
 copies an object to an uninitialized area of memory, defined by a start and a count
(function template)
(C++20)
 copies an object to an uninitialized area of memory, defined by a start and a count
(niebloid)
(C++17)
 moves a range of objects to an uninitialized area of memory
(function template)
(C++20)
 moves a range of objects to an uninitialized area of memory
(niebloid)
(C++17)
 moves a number of objects to an uninitialized area of memory
(function template)
(C++20)
 moves a number of objects to an uninitialized area of memory
(niebloid)
(C++17)
 constructs objects by default-initialization in an uninitialized area of memory, defined by a range
(function template)
(C++20)
 constructs objects by default-initialization in an uninitialized area of memory, defined by a range
(niebloid)
(C++17)
 constructs objects by default-initialization in an uninitialized area of memory, defined by a start and a count
(function template)
(C++20)
 constructs objects by default-initialization in an uninitialized area of memory, defined by a start and count
(niebloid)
(C++17)
 constructs objects by value-initialization in an uninitialized area of memory, defined by a range
(function template)
(C++20)
 constructs objects by value-initialization in an uninitialized area of memory, defined by a range
(niebloid)
(C++17)
 constructs objects by value-initialization in an uninitialized area of memory, defined by a start and a count
(function template)
(C++20)
 constructs objects by value-initialization in an uninitialized area of memory, defined by a start and a count
(niebloid)
(C++17)
 destroys a range of objects
(function template)
(C++20)
 destroys a range of objects
(niebloid)
(C++17)
 destroys a number of objects in a range
(function template)
(C++20)
 destroys a number of objects in a range
(niebloid)
(C++17)
 destroys an object at a given address
(function template)
(C++20)
 destroys an object at a given address
(niebloid)
(C++20)
 creates an object at a given address
(function template)
(C++20)
 creates an object at a given address
(niebloid)

Random number generation

Defined in header <random>
(C++26)
 fills a range with random numbers from a uniform random bit generator
(niebloid)

Notes

Feature-test macro Value Std Feature
__cpp_lib_algorithm_iterator_requirements 202207L (C++23) Ranges iterators as inputs to non-Ranges algorithms
__cpp_lib_clamp 201603L (C++17) std::clamp
__cpp_lib_constexpr_algorithms 201806L (C++20) Constexpr for algorithms
202306L (C++26) Constexpr stable sorting
__cpp_lib_algorithm_default_value_type 202403L (C++26) List-initialization for algorithms
__cpp_lib_freestanding_algorithm 202311L (C++26) Freestanding facilities in <algorithm>
__cpp_lib_robust_nonmodifying_seq_ops 201304L (C++14) Making non-modifying sequence operations more robust (two-range overloads for std::mismatch, std::equal and std::is_permutation)
__cpp_lib_sample 201603L (C++17) std::sample
__cpp_lib_shift 201806L (C++20) std::shift_left and std::shift_right

C library

Defined in header <cstdlib>
sorts a range of elements with unspecified type
(function)
searches an array for an element of unspecified type
(function)

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 193 C++98 heap required *first to be the largest element there can be elements
equal to *first
LWG 2150 C++98 the definition of a sorted sequence was incorrect corrected
LWG 2166 C++98 the heap requirement did not match the
definition of max heap closely enough 		requirement improved

See also

C documentation for Algorithms
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