C

C
1234qwer1234qwer4 · CC BY-SA 4.0 · source
Designer	Dennis Ritchie
Developer	Bell Labs
First appeared	1972
Paradigm	Procedural programming, Structured programming
Typing	Static typing, Weak typing
Influenced by	B programming language, ALGOL 68, BCPL
Influenced	C++, Objective-C, C#, Java, Linux kernel, Unix

C

C is a general-purpose, procedural programming language designed for system programming and portable application development. Created in the early 1970s at Bell Labs by Dennis Ritchie and colleagues, C provided low-level access to memory, simple lexical structure, and a minimal runtime, enabling the implementation of operating systems and compilers such as Unix and early BSD. Over subsequent decades, C has shaped a wide array of languages and projects, influencing C++, Objective-C, Java, C#, Linux kernel, and numerous standards bodies and implementations.

History

C evolved from earlier work on BCPL and B programming language within Bell Labs by researchers including Ken Thompson and Dennis Ritchie. Development coincided with the rewriting of Unix from Assembly language to a higher-level language, enabling portability across different computer architectures such as the DEC PDP-11. The language's early informal specification culminated in the 1978 book by Brian Kernighan and Dennis Ritchie, which popularized C and served as a de facto reference. Formal standardization efforts led to the American National Standards Institute (ANSI) committee X3J11 producing ANSI C in 1989, later adopted by the International Organization for Standardization as ISO/IEC 9899:1990. Subsequent revisions produced C99 and C11, each standardized through ISO processes and influenced by implementers at projects like GNU Project and vendors such as Microsoft and ARM Holdings.

Language Overview

C provides a small core of keywords, a lexical grammar with identifiers and punctuators, and a model of computation built around expressions, statements, and functions. The language exposes features such as pointer arithmetic, manual memory management through routines like malloc and free originating from Unix libraries, and direct interaction with hardware via bitwise operators and inline assembly in many compilers. Its type system includes scalar types (int, char, float), derived types (arrays, pointers, function types), aggregate types (struct, union), and the typedef mechanism; these features were applied in systems like the VAX port of BSD and embedded systems produced by firms such as Microchip Technology and Texas Instruments. The language's design emphasizes efficiency, predictable translation to machine code, and expressiveness for systems tasks, which made it a lingua franca for projects such as Apache HTTP Server, SQLite, and GCC.

Syntax and Semantics

C's syntax uses a block-structured grammar with semicolon-terminated statements, block delimiters using braces, and function prototypes for external linkage conventions standardized across implementations like GCC and Clang. The semantics define sequence points, undefined behavior, and implementation-defined behavior—concepts critical for developers working on projects such as the Linux kernel and OpenSSL where low-level assumptions affect security and portability. Expression evaluation rules, storage duration categories (automatic, static, dynamic), and linkage specifications determine symbol visibility in compilation units as practiced in build systems like make and CMake. The standard library's headers and macro conventions influence ABI decisions across platforms including x86 architecture, ARM architecture, and PowerPC.

Standard Library and Runtime

The C standard library provides standardized headers for input/output, string handling, mathematical functions, memory allocation, and time utilities, originally developed and refined in environments like Unix System V and distributed with toolchains from the GNU Project and Microsoft Visual Studio. Key components such as stdio.h, stdlib.h, string.h, and math.h define APIs used by applications ranging from Nginx to embedded firmwares by STMicroelectronics. The runtime model is minimal: program startup invokes a main function, command-line arguments and environment pointers are passed in implementations used by compilers from Intel Corporation and ARM Ltd., and program termination invokes cleanup functions. Delegation of I/O buffering, locale-aware behaviors, and wide-character support evolved through collaboration between standards committees and implementers including POSIX and vendor libraries.

Implementations and Compilers

Major C compilers and toolchains include the GNU Compiler Collection (GCC), Clang from the LLVM Project, and proprietary compilers from Microsoft (MSVC) and Intel Corporation (ICC). Each implementation targets multiple operating systems such as Linux, Windows NT, and macOS and architectures including x86-64 and ARM64. Cross-compilation toolchains support embedded targets from vendors like NXP Semiconductors and Renesas Electronics. Formal verification and static analysis tools—exemplified by projects at NASA and academic groups at MIT and University of Cambridge—address undefined behavior and security vulnerabilities detected in large codebases such as OpenSSL and OpenBSD.

Applications and Influence

C's portability and performance made it foundational for operating systems, language runtimes, databases, and network services. The Unix family and Linux kernel owe much of their implementation to C; database engines like PostgreSQL and MySQL and web servers including Apache HTTP Server and Nginx are written largely in C. Embedded firmware for microcontrollers from Atmel and STMicroelectronics frequently uses C for direct hardware control. C's syntax, semantics, and standard library shaped successor languages such as C++, Objective-C, Java, and C#, and influenced standards organizations, compiler development, and software engineering practices across academia and industry, including initiatives at Bell Labs, DARPA, and major technology firms like Google and Microsoft.

Category:Programming languages