stdlib

In programming, the stdlib, short for standard library, is the collection of core APIs and modules that accompany a language or runtime. It provides portable, widely useful functionality that developers rely on across platforms, from basic data types and input/output to higher‑level utilities. The stdlib is typically shipped with the language implementation and evolves along with the language standard.

It covers a broad range of domains, including input/output, strings and text processing, data structures and algorithms, mathematics, date and time handling, file systems, networking, concurrency and synchronization, error handling, and serialization. The exact contents and organization vary by language, and some features may be optional or restricted in certain environments (for example, embedded or no_std configurations).

Examples across languages illustrate the varying use of the term. In C, the standard library is defined by the ISO C standard and provides headers such as stdio.h, stdlib.h, string.h and math.h. In Python, the Python Standard Library comprises modules like sys, os, json, datetime, and itertools. In Rust, the standard library (the std crate) offers collections, I/O, threading, and concurrency primitives, with a no_std subset available for bare-metal or embedded targets.

Maintained by language developers and, for some languages, formal standardization efforts, the stdlib is distinct from third‑party libraries. It is generally versioned and documented, with deprecation and compatibility policies to preserve program portability across environments running the language runtime or compiler.