emcc

compile C/C++ to WebAssembly or JavaScript

TLDR

Compile C to WebAssembly

$ emcc [input.c] -o [output.wasm]

Compile to JavaScript

$ emcc [input.c] -o [output.js]

Compile with HTML harness

$ emcc [input.c] -o [output.html]

Compile C++

$ em++ [input.cpp] -o [output.js]

Optimize for size

$ emcc -Os [input.c] -o [output.wasm]

Optimize for speed

$ emcc -O3 [input.c] -o [output.wasm]

Export specific functions

$ emcc -sEXPORTED_FUNCTIONS=['_main','_myFunc'] [input.c] -o [output.js]

emcc (Emscripten Compiler Frontend) compiles C and C++ code to WebAssembly (Wasm) or JavaScript using LLVM and Emscripten. It enables running native code in web browsers and other Wasm runtimes.Emscripten provides a compatibility layer for POSIX APIs, OpenGL (via WebGL), and SDL. It can compile entire codebases including games and applications to run in browsers.

PARAMETERS

-o file

Output file (.js, .wasm, .html).

-O0 to -O3, -Os, -Oz

Optimization levels.

-s SETTING=VALUE

Emscripten-specific settings.

-I dir

Include directory.

-L dir

Library directory.

-l lib

Link library.

-g

Generate debug information.

--preload-file path

Preload file into virtual filesystem.

--embed-file path

Embed file in output.

-sMODULARIZE

Output as ES6 module.

CONFIGURATION

.emscripten

Emscripten configuration file containing SDK paths and compiler settings.

CAVEATS

Not all C/C++ features work identically. File system access requires virtual filesystem. Threading needs SharedArrayBuffer. Performance differs from native. Large applications may have long compile times. Browser security restrictions apply.

HISTORY

Emscripten was created by Alon Zakai at Mozilla in 2011, initially targeting asm.js before WebAssembly existed. When WebAssembly launched in 2017, Emscripten became the primary compiler toolchain for bringing C/C++ to the web.