C++ Standard Library

In the C++ programming language, the C++ Standard Library is a collection of classes and functions, which are written in the core language and part of the C++ ISO Standard itself.

Overview

The C++ Standard Library provides several generic containers, functions to use and manipulate these containers, function objects, generic strings and streams (including interactive and file I/O), support for some language features, and functions for common tasks such as finding the square root of a number. The C++ Standard Library also incorporates most headers of the ISO C standard library ending with "", but their use was deprecated (reverted the deprecation since C++23). C++23 instead considers these headers as useful for interoperability with C, and recommends against their usage outside of programs that are intended to be both valid C and C++ programs. No other headers in the C++ Standard Library end in "". Features of the C++ Standard Library are declared within the <code>std</code> namespace.

The C++ Standard Library is based upon conventions introduced by the Standard Template Library (STL), and has been influenced by research in generic programming and developers of the STL such as Alexander Stepanov and Meng Lee. Although the C++ Standard Library and the STL share many features, neither is a strict superset of the other. The design of the C++ standard library, much like the C standard library, is minimalistic, and contains only core features for programming, lacking most of the more specialised features offered by the Java standard library or C# standard library. For more features, some third-party libraries such as Boost libraries and POCO C++ Libraries, which offer additional features, may be used to supplement the standard library. An implementation for a C++ standard library header is described as "freestanding" if the execution of the program does not rely on an operating system.

A noteworthy feature of the C++ Standard Library is that it not only specifies the syntax and semantics of generic algorithms, but also places requirements on their performance. These performance requirements often correspond to a well-known algorithm, which is expected but not required to be used. In most cases this requires linear time O(n) or linearithmic time O(n log n), but in some cases higher bounds are allowed, such as quasilinear time O(n log<sup>2</sup> n) for stable sort (to allow in-place merge sort). Previously, sorting was only required to take O(n log n) on average, allowing the use of quicksort, which is fast in practice but has poor worst-case performance, but introsort was introduced to allow both fast average performance and optimal worst-case complexity, and as of C++11, sorting is guaranteed to be at worst linearithmic. In other cases requirements remain laxer, such as selection, which is only required to be linear on average (as in quickselect), not requiring worst-case linear as in introselect.

The C++ Standard Library underwent ISO standardization as part of the C++ ISO Standardization effort in the 1990s. Since 2011, it has been expanded and updated every three years with each revision of the C++ standard.

C++20 specifies the introduction of standard library header units, and C++23 adds full module support for the standard library.

Implementations

{| class="wikitable sortable"

! Name || Organization || Homepage || Acronym || Licence || Latest release

| GNU C++ Standard Library

|| GNU Project and Free Software Foundation

|| [https://gcc.gnu.org/]

|| libstdc++

|| GPLv3 with GCC Runtime Library Exception

|| New major release once per year

| LLVM C++ Standard Library

|| LLVM Developer Group

|| [https://libcxx.llvm.org/]

|| libc++

|| Apache License 2.0 with LLVM Exceptions

|| Every 2 weeks

| NVIDIA C++ Standard Library

|| Nvidia

|| [https://github.com/NVIDIA/cccl/tree/main/libcudacxx]

|| libcudacxx

|| Apache License 2.0 with LLVM Exceptions

| Microsoft C++ Standard Library

|| Microsoft

|| [https://github.com/microsoft/STL]

|| MSVC STL

|| Apache License 2.0 with LLVM Exceptions

|| Daily

| HPX C++ Standard Library for Parallelism and Concurrency

|| STELLAR Group

|| [https://github.com/STEllAR-GROUP/hpx]

|| HPX

|| Boost Software License 1.0

| Electronic Arts Standard Template Library

|| Electronic Arts

|| [https://github.com/electronicarts/EASTL]

|| EASTL

|| BSD 3-Clause License

| Dinkum C++ Library

|| Dinkumware

|| [http://www.dinkumware.com/]

|| Unknown

|| Commercial

|| Unknown

| Cray C++ Standard Library

|| Cray User Group

|| [https://cug.org/]

|| Unknown

|| Commercial

|| Unknown

Discontinued

Apache C++ Standard Library

The Apache C++ Standard Library is another open-source implementation. It was originally developed commercially by Rogue Wave Software and later donated to the Apache Software Foundation. However, after more than five years without a release, the board of the Apache Software Foundation decided to end this project and move it to Apache Attic.

Namespace organisation

The C++ standard library is placed inside the <code>std</code> namespace. <code>std</code> was historically a flat namespace (unlike other languages like Java and C#, which extensively divide their respective standard libraries along nomenclatural, hierarchical lines), but since C++11 it has been further divided into sub-namespaces within it:

<code>std</code> (the main namespace of the standard library)
<code>std::chrono</code> (contains facilities for the date and time library)
<code>std::contracts</code> (contains facilities for reporting information on contract violations)
<code>std::execution</code> (contains the execution control library for asynchronous execution, including <code>task<T></code>)
<code>std::execution::system_context_replaceability</code> (allows for replacement of the default implement of the parallel scheduler)
<code>std::filesystem</code> (contains facilities for working with file system manipulation, including <code>directory_entry</code>, <code>path</code>, etc.)
<code>std::linalg</code> (contains facilities for linear algebra)
<code>std::literals</code> (inlined namespace containing various operators for creating literals of an object)
<code>std::literals::chrono_literals</code> (inlined namespace containing various operators for creating literals of duration objects)
<code>std::literals::complex_literals</code> (inlined namespace containing various operators for creating literals of imaginary numbers)
<code>std::literals::string_literals</code> (inlined namespace containing various operators for creating literals of string objects)
<code>std::literals::string_view_literals</code> (inlined namespace containing various operators for creating literals of string-view objects)
<code>std::meta</code> (contains facilities for static (compile-time) reflection with the <code>info</code> type representing reflection metadata)
<code>std::numbers</code> (contains all numeric constants, such as <code>pi</code>, <code>e</code>, etc.)
<code>std::placeholders</code> (contains all placeholder objects <code>_1</code>, <code>_2</code>, ..., up to an implementation-defined maximum <code>_N</code>)
<code>std::pmr</code> (contains symbols for polymorphic memory resources, for flexible runtime-configured allocation, as well as versions of the standard library types using <code>polymorphic_allocator</code> as the allocator)
<code>std::ranges</code> (contains symbols for working over ranges, which extend the algorithm/iterator libraries)
<code>std::ranges::views</code> (contains symbols for range adapters for creating views, for lazy collection manipulation without copies; also aliased as <code>std::views</code>)
<code>std::regex_constants</code> (contains various regular expression customisation constants, such as <code>ECMAScript</code>, <code>awk</code>, <code>grep</code>, etc.)
<code>std::rel_ops</code> (contains automatically generated comparison operators, deprecated since C++20)
<code>std::this_thread</code> (contains facilities for manipulating the current thread)

There is also a <code>std::experimental</code> namespace, with further sub-namespaces in <code>std::experimental::*</code> for various pre-standardised/technical specification features which may be implemented by some compiler vendors.

Standard modules

Although modules were first introduced in C++20, standard library modules were only standardised as part of the language in C++23. Prior to that, standard library header units were specified for C++20, but most compiler vendors support backporting standard library modules to C++20. These named modules were added to include all items declared in both global and <code>std</code> namespaces provided by the importable standard headers. Macros are not allowed to be exportable, so users have to manually include or import headers that emit macros for use, or can be alternatively exported as compile-time constants.

The C++ standard has reserved <code>std</code> and <code>std.*</code> as module names, however most compilers allow a flag to override this.

The standard library modules are:

{| class="wikitable"

! Name !! Since !! Description

|| C++23

|| Exports all declarations in namespace <code>std</code> and global storage allocation and deallocation functions that are provided by the importable C++ library headers including C library facilities (although declared in standard namespace).

|| C++23

|| Exports the same declarations as the named module <code>std</code>, and additionally exports functions in global namespace in C library facilities. It thus contains "compat" in the name, meaning compatibility with C.

<code>std.compat</code> is not a submodule of <code>std</code>, but is named so to indicate the association the module bears to the <code>std</code> module (as a "compatibility" version of it). Despite there being only one module for the entire standard library, it has been proposed that additional modules providing other subsets of the standard library be added.

Standard headers

The following files contain the declarations of the C++ Standard Library.

Legend:<br>

: Deprecated<br>

: Removed

General

Components that C++ programs may use for increased features.

{| class="wikitable"

! Name !! Since !! Description

|| C++17

|| Provides a type-erased class <code>any</code>.

|| C++98

|| Related to <code><errno.h></code>. For testing error codes reported by library functions.

|| C++11

|| Provides time elements, such as <code>duration</code>, <code>time_point</code>, and clocks. Since C++20, additional temporal features were added, including calendars, time zones, more clocks, and time formatting.

|| C++20

|| Provides fundamental library concepts.

|| C++26

|| Provides design by contract features.

|| C++98

|| Related to <code><setjmp.h></code>. Declares the macros <code>setjmp</code> and <code>longjmp</code>, which are used for non-local exits.

|| C++98

|| Related to <code><signal.h></code>. Defines signal-handling functions.

| style="background:#F99" |

| style="background:#F99" | C++98

| style="background:#F99" | Related to <code><stdalign.h></code>. For querying and specifying the alignment of objects. Deprecated in C++17, removed in C++20.

| style="background:#F99" |

| style="background:#F99" | C++98

| style="background:#F99" | Related to <code><stdbool.h></code>. Defines a Boolean data type. Deprecated in C++17, removed in C++20.

|| C++98

|| Related to <code><stddef.h></code>. Defines several useful types and macros.

|| C++98

|| Related to <code><stdint.h></code>. Defines exact-width integer types.

|| C++98

|| Related to <code><time.h></code>. Defines date- and time-handling functions.

|| C++26

|| Provides fundamental library concepts.

|| C++23

|| Provides class template <code>expected</code>, a result type.

|| C++98

|| Provides several function objects, designed for use with the standard algorithms.

|| C++23

|| Provides a coroutine generator that additionally supports nested yield operations on ranges.

|| C++98

|| Provides facilities for memory management in C++, including the class template <code>unique_ptr</code>.

|| C++17

|| Provides facilities for creating polymorphic memory allocators whose behaviors can change at runtime.

|| C++17

|| Provides class template <code>optional</code>, an optional type.

|| C++11

|| Provides <code>scoped_allocator_adaptor</code>.

|| C++23

|| Provides stack trace operations.

|| C++98

|| Contains standard exception classes such as <code>logic_error</code> and <code>runtime_error</code>.

|| C++11

|| Defines <code>error_code</code> and features relating to its usage.

|| C++11

|| Provides a class template <code>tuple</code>, a tuple.

|| C++11

|| Provides metaprogramming facilities working with types.

|| C++98

|| The utility file provides various utilities: class template <code>pair</code> (two-member tuples), compile-time integer sequences, helpers in constructing vocabulary types, functions such as <code>move</code> and <code>forward</code>, and many more. The namespace <code>std::rel_ops</code> for automatically generating comparison operators is deprecated in C++20 in favor of new defaulted comparison operators.

|| C++17

|| Provides a class template <code>variant</code>, a tagged union type.

Language support

Components that C++ programs may use for support during development.

{| class="wikitable"

! Name !! Since !! Description

|| C++98

|| Related to <code><assert.h></code>. Declares the assert macro, used to assist with detecting logical errors and other types of bugs while debugging a program.

|| C++98

|| Related to <code><errno.h></code>. Defines a set of functions for controlling floating-point environment.

|| C++98

|| Related to <code><float.h></code>. Defines macro constants specifying the implementation-specific properties of the floating-point library.

|| C++98

|| Related to <code><inttypes.h></code>. Defines exact-width integer types.

| style="background:#F99" |

| style="background:#F99" | C++98

| style="background:#F99" | Related to <code><iso646.h></code>. Defines several macros that implement alternative ways to express several standard tokens. For programming in ISO 646 variant character sets. Removed in C++20.

|| C++98

|| Related to <code><limits.h></code>. Defines macro constants specifying the implementation-specific properties of the integer types.

|| C++20

|| Provides three-way comparison operator support.

|| C++20

|| Provides coroutine support.

|| C++26

|| Provides debugging support, such as breakpoints and other mechanisms to aid debuggers.

|| C++98

|| Provides several types and functions related to exception handling, including <code>exception</code>, the base class of all exceptions thrown by the Standard Library.

|| C++11

|| Provides initializer list constructor support through <code>initializer_list</code>.

|| C++98

|| Provides the class template <code>numeric_limits</code>, used for describing properties of fundamental numeric types.

|| C++26

|| Provides reflective programming capabilities as well as symbol metadata and annotations.

|| C++98

|| Provides operators <code>new</code> and <code>delete</code> and other functions and types for placement allocation.

|| C++20

|| Provides source location information.

|| C++23

|| Provides conditional support for extended floating-point types.

|| C++98

|| Provides facilities for working with C++ run-time type information.

|| C++20

|| Provides information through macros about the provider's implementation of language features and the standard library.

Containers/collections

Components that C++ programs may use for container data structures.

{| class="wikitable"

! Name !! Since !! Description

|| C++11

|| Provides the container class template <code>array</code>, a container for a fixed-size array.

|| C++98

|| Provides the specialized container class <code>bitset</code>, a fixed-size bit array.

|| C++98

|| Provides the container class template <code>deque</code>, a double-ended queue.

|| C++23

|| Provides the container adapter class templates <code>flat_map</code> and <code>flat_multimap</code>.

|| C++23

|| Provides the container adapter class templates <code>flat_set</code> and <code>flat_multiset</code>.

|| C++11

|| Provides the container class template <code>forward_list</code>, a singly linked list.

|| C++26

|| Provides the class <code>inplace_vector</code>, analogous to <code>vector</code> with a fixed capacity defined at compile time.

|| C++26

|| Provides the class <code>hive</code>, which reuses erased elements' memory

|| C++98

|| Provides the container class templates <code>map</code> and <code>multimap</code>, sorted associative array and multimap.

|| C++23

|| Provides the class template <code>mdspan</code>, analogous to <code>span</code> but for multidimensional views.

|| C++98

|| Provides the container adapter class <code>queue</code>, a single-ended queue, and <code>priority_queue</code>, a priority queue.

|| C++98

|| Provides the container class templates <code>set</code> and <code>multiset</code>, sorted associative containers or sets.

|| C++20

|| Provides the class template <code>span</code>, a non-owning view that refers to any contiguous range.

|| C++98

|| Provides the container adapter class <code>stack</code>, a stack.

|| C++11

|| Provides the container class template <code>unordered_map</code> and <code>unordered_multimap</code>, hash tables.

|| C++11

|| Provides the container class template <code>unordered_set</code> and <code>unordered_multiset</code>.

|| C++98

|| Provides the container class template <code>vector</code>, a dynamic array.

Iterators and ranges

Components that C++ programs may use to manipulate iterators, ranges, and algorithms over ranges and containers.

{| class="wikitable"

! Name !! Since !! Description

|| C++98

|| Provides definitions of many algorithms for use with containers and other ranges.

|| C++17

|| Provides execution policies for parallelized algorithms. Expanded in C++26 with an execution control framework for asynchronous operations and tasks.

|| C++98

|| Provides classes and templates for working with iterators.

|| C++98

|| Generalized numeric algorithms.

|| C++20

|| Provides ranges facilities and lazily evaluated adapters.

Localisation

Components that C++ programs may use for localisation and character encoding manipulation.

{| class="wikitable"

! Name !! Since !! Description

|| C++98

|| Related to <code><locale.h></code>. Defines localization functions.

| style="background:#F99" |

| style="background:#F99" | C++11

| style="background:#F99" | Provides code conversion facets for various character encodings. Deprecated since C++17, removed in C++26.

|| C++98

|| Defines classes and declares functions that encapsulate and manipulate the information peculiar to a locale.

|| C++26

|| Provides text encoding identifications with the IANA Character Sets registry.

Strings

Components that C++ programs may use for string manipulation.

{| class="wikitable"

! Name !! Since !! Description

|| C++98

|| Related to <code><ctype.h></code>. Defines set of functions used to classify characters by their types or to convert between upper and lower case in a way that is independent of the used character set (typically ASCII or one of its extensions, although implementations utilizing EBCDIC are also known).

|| C++17

|| Provides a locale-independent, non-allocating, and non-throwing string conversion utilities from/to integers and floating point.

|| C++98

|| Related to <code><string.h></code>. Defines string-handling functions.

|| C++98

|| Related to <code><uchar.h></code>. Types and functions for manipulating Unicode characters.

|| C++98

|| Related to <code><wchar.h></code>. Defines wide-string-handling functions.

|| C++98

|| Related to <code><wctype.h></code>. Defines set of functions used to classify wide characters by their types or to convert between upper and lower case.

|| C++20

|| Provides string formatting utilities.

|| C++98

|| Provides the C++ standard <code>string</code> classes and templates.

|| C++17

|| Provides <code>string_view</code> classes, representing an immutable non-owning view to any string.

|| C++11

|| Provides utilities for pattern matching strings using regular expressions.

Streams, files, and input/output

Components that C++ programs may use for input/output manipulation and file manipulation.

{| class="wikitable"

! Name !! Since !! Description

|| C++98

|| Related to <code><stdio.h></code>. Defines core input and output functions.

|| C++17

|| Provides facilities for file system operations and their components.

|| C++98

|| Provides facilities for file-based input and output. See fstream.

|| C++98

|| Provides facilities to manipulate output formatting, such as the base used when formatting integers and the precision of floating-point values.

|| C++98

|| Provides several types and functions basic to the operation of iostreams.

|| C++98

|| Provides forward declarations of several I/O-related class templates.

|| C++98

|| Provides C++ input and output fundamentals. See iostream.

|| C++98

|| Provides <code>istream</code> and other supporting classes for input.

|| C++98

|| Provides <code>ostream</code> and other supporting classes for output.

|| C++23

|| Provides formatted output utilities such as <code>print</code> supported for both C and C++ streams.

|| C++23

|| Provides <code>spanstream</code> and other fixed character buffer I/O streams.

|| C++98

|| Provides <code>stringstream</code> and other supporting classes for string manipulation.

|| C++98

|| Provides reading and writing functionality to/from certain types of character sequences, such as external files or strings.

| style="background:#F99" |

| style="background:#F99" | C++98

| style="background:#F99" | Provides input/output operations on array-backed streams. Deprecated in C++98, removed in C++26.

|| C++20

|| Provides <code>osyncstream</code> and other supporting classes for synchronized output streams.

Thread support library

Components that C++ programs may use for threading and concurrent programming.

{| class="wikitable"

! Name !! Since !! Description

|| C++11

|| Provides class template <code>atomic</code>, its several template specializations, and more atomic operations.

|| C++20

|| Provides <code>barrier</code>, a reusable thread barrier.

|| C++98

|| Related to <code><stdarg.h></code>. For atomic operations on data shared between threads.

|| C++11

|| Provides components that a C++ program can use to retrieve in one thread the result (value or exception) from a function that has run in the same thread or another thread, such as <code>future</code>.

|| C++26

|| Provides hazard pointers via <code>hazard_pointer</code>.

|| C++20

|| Provides <code>latch</code>, a single-use thread barrier.

|| C++11

|| Provides mechanisms for mutual exclusion: mutexes, locks, and <code>call_once</code>.

|| C++26

|| Provides read-copy-update mechanisms for safe reclamation.

|| C++14

|| Provides facility for shared mutual exclusion.

|| C++20

|| Provides semaphore utilities for non-negative resource count.

|| C++20

|| Provides components that can be used to asynchronously request that an operation stops execution in a timely manner.

|| C++11

|| Provide class <code>thread</code> for working with threads. Later expanded in C++20 with <code>jthread</code>, which automatically joins upon destruction. Also contains namespace <code>std::this_thread</code> for operations on the currently executing thread.

Numerics library

Components that C++ programs may use to perform seminumerical or mathematical operations.

{| class="wikitable"

! Name !! Description

|| C++20

|| Provides bit manipulation facilities.

| style="background:#F99" |

| style="background:#F99" | C++98

| style="background:#F99" | Related to <code><complex.h></code>. Defines a set of functions for manipulating complex numbers. Deprecated in C++17, removed in C++20.

|| C++98

|| Related to <code><math.h></code>. Defines common mathematical functions. Extends <code><math.h></code>, containing special mathematical functions such as Bessel functions and the Riemann zeta function.

|| C++98

|| Defines a class template <code>complex</code>, and numerous functions for representing and manipulating complex numbers.

| style="background:#F99" |

| style="background:#F99" | C++98

| style="background:#F99" | Related to <code><tgmath.h></code>. Defines type-generic mathematical functions. Deprecated in C++17, removed in C++20.

|| C++26

|| Provides linear algebra facilities.

|| C++20

|| Provides mathematical constants defined in namespace <code>std::numbers</code>.

|| C++26

|| Provides data-parallel types (Single instruction, multiple data or SIMD) and operations on these types.

|| C++11

|| Facility for generating (pseudo-)random numbers and distributions.

|| C++11

|| Provides compile-time rational arithmetic based on class templates.

|| C++98

|| Defines five class templates (<code>valarray</code>, <code>slice_array</code>, <code>gslice_array</code>, <code>mask_array</code>, and <code>indirect_array</code>), two classes (<code>slice</code> and <code>gslice</code>), and a series of related function templates for representing and manipulating arrays of values.

C standard library

Each header from the C Standard Library is included in the C++ Standard Library under a different name, generated by removing the file extension, and adding a at the start; for example, '<code>time.h</code>' becomes '<code>ctime</code>'. The only difference between these headers and the traditional C Standard Library headers is that where possible the functions should be placed into the <code>std::</code> namespace. In ISO C, functions in the standard library are allowed to be implemented by macros, which is not allowed by ISO C++.

Usage of the C headers with the file extension is legal in C++ and used for compatibility.

The following headers are special C compatibility headers which do not have a corresponding C++ naming convention, meaning that the C headers must be used if the header is necessary.

{| class="wikitable"

! Name !! Since !! Description

|| C++23

|| For atomic operations on data shared between threads.

|| C++26

|| For manipulating and processing bits and bit sequences.

|| C++26

|| For checked integers.

|| C++26

|| For determining the length of a C array.

The C headers <code><stdnoreturn.h></code> and <code><threads.h></code> do not have C++ equivalents and their C headers are not supported in C++.

C++ does not provide the C POSIX library as part of any standard, however it is legal to use in a C++ program. If used in C++, the POSIX headers are not prepended with a "" at the beginning of the name, and all contain the suffix in the header name. Most headers in the POSIX library typically have a C++ equivalent implementation, such as <code><regex></code> rather than <code><regex.h></code>.

Networking TS library

The following headers are defined in the C++ networking TS, itself based on the <code>boost::asio</code> library from Boost, which is not standardised in C++ yet. Despite this, it is provided by some vendors, such as GCC. The symbols are placed in <code>std::extensions::net</code>.

{| class="wikitable"

! Name !! Description

|| Contains forward declarations of Networking TS components.

|| Provides asynchronous models for networking.

|| Provides basic I/O services for networking.

|| Provides timer operations for networking.

|| Provides buffers and buffer-oriented streams for networking.

|| Provides sockets and socket streams for networking.

|| Provides internet protocols for networking.

|| Includes all Networking TS headers.

Notes

References

External links

C++ Standard Library reference
Microsoft C++ Standard Library Reference
Rogue Wave SourcePro C++ documentation
Apache C++ Standard Library Wiki, retired 15 May 2014 (based on Rogue Wave C++ Standard Library 4.1.0)
STLport C++ Standard Library documentation
The GNU C++ Library online documentation
LLVM/Clang C++ Standard Library documentation

C++ Standard Library

Overview

Implementations

Discontinued

Apache C++ Standard Library

See also

Namespace organisation

Standard modules

Standard headers

General

Language support

Containers/collections

Iterators and ranges

Localisation

Strings

Streams, files, and input/output

Thread support library

Numerics library

C standard library

Networking TS library

See also

Notes

References

Further reading

External links