C

In simple terms

C is the language that operating systems, compilers, embedded firmware, and most performance-critical infrastructure are written in. It’s small, fast, portable, and unforgiving: there’s no garbage collector, no memory safety, no string class — you manage memory by hand and the compiler trusts you completely. That trade-off (great power, great responsibility) made it the default systems language for fifty years.

More detail

Dennis Ritchie created C at Bell Labs (1972) to rewrite Unix. The design goals were portability (the same C code should compile on different machines) and giving the programmer direct access to the machine without forcing assembly.

Defining characteristics:

• Manual memory management — malloc / free, no GC, no bounds checking.
• Pointers — first-class, arithmetic on them is allowed, foot-guns abound.
• Static typing — but weak: types coerce eagerly and silently.
• Tiny standard library — much smaller than modern languages; “do everything yourself” by design.
• Preprocessor — #include, #define, #ifdef. Crude but ubiquitous.
• No exceptions, no closures, no generics — you build all of those by hand if you need them.

Standards: K&R (1978), ANSI C89, C99, C11, C17, C23. Most embedded code is still C99; most kernels target a slightly newer subset.

The compiler family:

• gcc — the GNU C compiler; the default on Linux and most Unix.
• clang — LLVM-based; better diagnostics, used by Apple, FreeBSD, and increasingly elsewhere.
• MSVC — Microsoft’s compiler for Windows.
• tcc, chibicc — small or pedagogical compilers.

Common safety footguns: buffer overflows, use-after-free, double-free, integer overflow, uninitialised reads, dangling pointers, signed-overflow undefined behaviour. Modern projects mitigate with -fsanitize=address, fuzzing, static analysis, and increasingly Rust for new code.

Why it matters

The Linux kernel, the BSDs, parts of macOS and Windows, almost every database engine, OpenSSL, SQLite, Redis, Postgres, most language runtimes (CPython, Ruby, PHP, V8, JVM), almost all embedded firmware — all written in C. Even when you don’t write C, the code you depend on is written in it.

Real-world examples

• SQLite is ~150 KB of C source code that runs in every smartphone, browser, and embedded device on Earth — the most-deployed database in the world.
• The Linux kernel is ~30 million lines of C and counting.
• Redis started as a few thousand lines of C and grew into one of the most-deployed in-memory databases.
• The CPython interpreter is C; PEP-7 (the C style guide) is still the standard for new contributions.

Common misconceptions

• “C is obsolete.” It is the most-deployed systems language by an enormous margin and will be for decades. Even where Rust is adopted, it usually coexists with C.
• “C is hard.” The language is small. What’s hard is writing correct C without modern tooling — UBSan, ASan, fuzzers, and a strict compiler are essentials, not luxuries.

Learn next

What turns C source into binaries: compiler. The machine resource C makes you manage directly: memory.