C Reference

Core language rules, standard library families, headers, and navigation paths for the C reference.

C is both a language specification and a standard library. This landing page is the top-level map for the C reference: start here when you need the right branch of the language, the right library family, or a faster route into headers and symbol indexes.

This root hub is intentionally broad. It points to the main language and library families first, then to the more specialized C-only indexes and bridge pages that still need deeper curation.

# Start Here

Language rules and syntax

Declarations, expressions, types, initialization, storage duration, functions, and the execution model of the language itself.

Declarations · Expressions · Initialization

Preprocessor and translation

Macro replacement, conditional inclusion, source file inclusion, line control, and the token-processing steps that happen before compilation.

#include · #define · Conditional inclusion

Choose by header family

Use the header and library-family routes when you know the facility area you need but not yet the exact function or macro name.

Strings · I/O · Numerics

Find by index

Jump to index-style routes when you already know the approximate symbol shape, macro family, or entry namespace.

C index · Keywords · Headers

# Language Vs. Library

Area	What it answers	Start with	Typical topics
Core language	How C code is parsed and evaluated: types, expressions, declarations, storage duration, initialization, conversions, and program structure.	Language	Arithmetic types, Declarations, Expressions, Lifetime
Preprocessor	How source text is transformed before the compiler sees the final translation unit.	Preprocessor	#include, Macro replacement, Conditional inclusion
Standard library	Which headers, functions, macros, and support types the C library provides.	String, I/O, Numerics	Memory, Time, Threads, Error handling
Reference aids	How to browse by keyword, header path, or index rather than by topic-first documentation flow.	Keywords, Headers, Index	Tokens, macros, aliases, compatibility entry points, and lookup shortcuts.

# Library Families

Strings and memory

Byte strings, wide strings, memory inspection and copying, and the boundary between raw memory and string-oriented APIs.

String · Memory · Types

Input and output

Streams, files, buffering, formatted I/O, byte/wide character functions, temporary files, and error-state handling.

fopen · fprintf · fflush

Numerics and math

Mathematical functions, complex arithmetic, floating-point environment, random number generation, and bit utilities.

Math · Complex · Floating-point environment

Time and date

Calendar time, broken-down time, clocks, formatting, and portable time measurements.

time · strftime · timespec_get

Concurrency and atomics

Thread creation and synchronization in C11+, plus the atomic object model, fences, lock-freedom, and memory order.

Thread support · Atomics · memory_order

Program support and diagnostics

Process control, environment interaction, termination behavior, assertions, errno, and runtime diagnostics.

Program utilities · Error handling · assert

# Headers And Indexes

Use case	Go here
You want to browse the C library by broad header path or compatibility route.	Header index
You already know the token or language keyword you need.	Keyword index
You want index-style C entry points and macro-oriented lookup paths.	C index
You need the C++ side of the reference instead of the C side.	C++ reference