mycc — A C-Subset Compiler for x86-64

A small but complete compiler written in plain C99 (no Lex, Yacc, or LLVM). mycc reads a C-subset source file and produces x86-64 AT&T assembly that assembles and runs on both Linux (ELF, System V) and Windows (PE/COFF, MinGW-w64) with ordinary gcc.

source.c ──> mycc ──> source.s ──> gcc ──> executable ──> exit code

What's inside

• Hand-written lexer, recursive-descent parser, scoped symbol table, semantic analysis, and code generator (~3,500 lines of C99).
• Types: int (64-bit) and char (signed, one byte); void functions.
• Statements: if/else, while, do/while, for (loop-local declarations), switch/case/default with fallthrough, break, continue, return, and nested blocks.
• Expressions: the full C precedence ladder — arithmetic, %, relational and equality, &&/|| (short-circuiting) and !, bitwise & | ^ ~, shifts << >>, the conditional ?:, ++/-- (prefix and postfix), and compound assignment (+= -= *= /= %= &= |= ^= <<= >>=).
• Programs: multiple functions with recursion, globals with constant-folded initializers, multi-declarator declarations, and block scoping.
• Literals: decimal, hexadecimal (0x…), and octal (0…) integers with optional u/l suffixes; character constants ('A', '\n', '\x41').
• Diagnostics: friendly errors with file:line:col, scope/main/ break/continue/switch validation, and rejection of non-constant global initializers.
• --dump-tokens / --dump-ast reveal the compiler's internals.
• Programs report results through their exit code (there is no printf).

Quick start (Windows / PowerShell)

cd "C:\Folder D\C_Compiler_Test_MiniProject\my_c_compiler"
.\build.bat        # builds mycc.exe
.\test.bat         # runs the positive + error test suites
.\showcase.bat     # end-to-end demo, returns 197

Quick start (Linux / macOS)

make               # builds ./mycc with gcc
make test          # runs the positive + error test suites
./mycc example.c -o demo.s
gcc -no-pie -o demo demo.s
./demo; echo $?    # prints 197

Set CC=/path/to/gcc to build with a specific compiler.

Continuous integration

Every push and pull request is built and tested on Linux and Windows (MSYS2/UCRT64) via .github/workflows/ci.yml.

Documentation

• instructions.md — full manual: language, build/test/showcase, troubleshooting.
• ROADMAP.md — planned phases: C-fidelity fixes, more language, I/O, optimization, diagnostics, and a true Windows calling convention.