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 ".h", 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 ".h". Features of the C++ Standard Library are declared within the  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.

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 log2 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.

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.

Standard modules
Ever since the modules were introduced in C++20, there has been no support for standard library modules until C++23. These named modules were added to include all items declared in both global and  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.


 * std:Exports all declarations in namespace  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).
 * std.compat:Exports the same declarations as the named module, and additionally exports functions in global namespace in C library facilities.

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

General

 * New in C++17. Provides a type-erased class.
 * New in C++11. Provides class template, its several template specializations, and more atomic operations.
 * Provides time elements, such as,  , and clocks. Since C++20, a hefty amount of temporal features were added: calendars, time zones, more clocks, and string chrono formatting.
 * New in C++20. Provides fundamental library concepts.
 * New in C++23. Provides class template, a result type.
 * Provides several function objects, designed for use with the standard algorithms.
 * New in C++23. Provides a coroutine generator that additionally supports nested yield operations on ranges.
 * Provides facilities for memory management in C++, including the class template.
 * :New in C++17. Provides facilities for creating polymorphic memory allocators whose behaviors can change at runtime.
 * New in C++17. Provides class template, an optional type.
 * :New in C++11. Provides.
 * New in C++23. Provides stack trace operations.
 * Contains standard exception classes such as  and , both derived from.
 * :New in C++11. Defines
 * New in C++11 and TR1. Provides a class template, a tuple.
 * :New in C++11. Provides metaprogramming facilities working with types.
 * Provides various utilities: class template  (two-member tuples), compile-time integer sequences, helpers in constructing vocabulary types, functions such as   and , and many more. The namespace   for automatically generating comparison operators is deprecated in C++20 in favor of new defaulted comparison operators.
 * New in C++17. Provides a class template, a tagged union type.

Language support

 * New in C++20. Provides three-way comparison operator support.
 * New in C++20. Provides coroutine support.
 * Provides several types and functions related to exception handling, including, the base class of all exceptions thrown by the Standard Library.
 * :New in C++11. Provides initializer list support.
 * Provides the class template, used for describing properties of fundamental numeric types.
 * Provides operators  and   and other functions and types composing the fundamentals of C++ memory management.
 * {{code|.
 * New in C++23. Provides conditional support for extended floating-point types.
 * Provides facilities for working with C++ run-time type information.
 * New in C++20. Provides information about the implementation of the C++ standard library.

Containers

 * New in C++11 and TR1. Provides the container class template, a container for a fixed sized array.
 * Provides the specialized container class, a bit array.
 * Provides the container class template, a double-ended queue.
 * :New in C++23. Provides the container adaptor class templates  and.
 * :New in C++23. Provides the container adaptor class templates  and.
 * :New in C++11 and TR1. Provides the container class template, a singly linked list.
 * Provides the container class template, a doubly linked list.
 * Provides the container class templates  and , sorted associative array and multimap.
 * New in C++23. Provides the class template, analogous to   but the view is multidimensional.
 * Provides the container adapter class, a single-ended queue, and  , a priority queue.
 * Provides the container class templates  and , sorted associative containers or sets.
 * New in C++20. Provides the class template, a non-owning view that refers to any contiguous range.
 * Provides the container adapter class, a stack.
 * :New in C++11 and TR1. Provides the container class template  and , hash tables.
 * :New in C++11 and TR1. Provides the container class template  and.
 * Provides the container class template, a dynamic array.

Iterators and Ranges

 * Provides definitions of many algorithms for use with containers and other ranges.
 * New in C++17. Provides execution policies for parallelized algorithms.
 * Provides classes and templates for working with iterators.
 * Generalized numeric algorithms.
 * New in C++20. Provides ranges facilities and lazily evaluated adaptors.

Localization

 * {{code|.
 * {{code| }}:Provides the C++ standard string classes and templates.
 * {{code|}}:New in C++17. Provides class template, an immutable non-owning view to any string.
 * {{code| }}:New in C++11. Provides utilities for pattern matching strings using regular expressions.

Streams, Files, and Input/Output

 * New in C++17. Provides facilities for file system operations and their components.
 * Provides facilities for file-based input and output. See fstream.
 * Provides facilities to manipulate output formatting, such as the base used when formatting integers and the precision of floating-point values.
 * Provides several types and functions basic to the operation of iostreams.
 * Provides forward declarations of several I/O-related class templates.
 * Provides C++ input and output fundamentals. See iostream.
 * Provides  and other supporting classes for input.
 * Provides  and other supporting classes for output.
 * New in C++23. Provides formatted output utilities such as  supported for both C and C++ streams.
 * New in C++23. Provides  and other fixed character buffer I/O streams.
 * Provides  and other supporting classes for string manipulation.
 * Provides reading and writing functionality to/from certain types of character sequences, such as external files or strings.
 * New in C++20. Provides  and other supporting classes for synchronized output streams.

Thread support library

 * New in C++20. Provides, a reusable thread barrier.
 * : New in C++11. In 32.6-1, condition variables provide synchronization primitives used to block a thread until notified by some other thread that some condition is met or until a system time is reached.
 * New in C++11. In 32.9.1-1, this section describes 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.
 * : New in C++26. Provides.
 * New in C++20. Provides, a single-use thread barrier.
 * New in C++11. In 32.5-1, this section provides mechanisms for mutual exclusion: mutexes, locks, and call once.
 * New in C++26. Provides read-copy-update mechanisms.
 * : New in C++14. Provides facitility for shared mutual exclusion.
 * New in C++20. Provides semaphore that models non-negative resource count.
 * : New in C++20. In 32.3.1-1, this section describes components that can be used to asynchronously request that an operation stops execution in a timely manner, typically because the result is no longer required. Such a request is called a stop request.
 * New in C++11. Provide class and namespace for working with threads.

Numerics library
Components that C++ programs may use to perform seminumerical operations.
 * New in C++20. Provides bit manipulation facility.
 * Defines a class template, and numerous functions for representing and manipulating complex numbers.
 * New in C++20. Provides mathematical constants defined in namespace.
 * New in C++11. Facility for generating (pseudo-)random numbers and distributions.
 * New in C++11. Provides compile-time rational arithmetic based on class templates.
 * Defines five class templates (, ,  ,  , and  ), two classes (  and  ), 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 .h, and adding a 'c' at the start; for example, 'time.h' becomes 'ctime'. The only difference between these headers and the traditional C Standard Library headers is that where possible the functions should be placed into the  namespace. In ISO C, functions in the standard library are allowed to be implemented by macros, which is not allowed by ISO C++.