clang

LLVM C/C++/Objective-C compiler

TLDR

Compile C program

$ clang [program.c] -o [program]

Compile with optimization

$ clang -O3 [program.c] -o [program]

Compile with debug info

$ clang -g [program.c] -o [program]

Enable all warnings

$ clang -Wall -Wextra [program.c] -o [program]

Compile C++ program

$ clang++ [program.cpp] -o [program]

clang is a C, C++, and Objective-C compiler based on the LLVM compiler infrastructure. It provides fast compilation, excellent diagnostics with clear error messages, and is designed as a drop-in replacement for GCC on most platforms.
Clang is known for its expressive error messages that include source highlighting, fix-it hints, and template backtrace improvements over GCC. Its modular library-based architecture enables reuse in tools like clang-format, clang-tidy, and clangd.
The compiler supports modern language standards (C17, C++20, C++23), sanitizers for detecting memory errors and undefined behavior at runtime, and extensive static analysis capabilities. It is the default compiler on macOS and FreeBSD and widely used on Linux.

PARAMETERS

-o file

Output file name

-c

Compile without linking

-g

Generate debug information

-O[level]

Optimization (0, 1, 2, 3, fast, s, z)

-std=standard

Language standard (c11, c17, c++17, c++20)

-Wall

Enable common warnings

-Wextra

Enable extra warnings

-Werror

Treat warnings as errors

-I dir

Add include directory

-L dir

Add library directory

-l lib

Link library

-fsanitize=type

Enable sanitizer (address, thread, memory, undefined)

OPTIMIZATION LEVELS

- -O0 - No optimization (default)
- -O1 - Basic optimization
- -O2 - Moderate optimization (recommended)
- -O3 - Aggressive optimization
- -Os - Optimize for size
- -Ofast - Maximum speed (may break standards)

WORKFLOW

$ # Simple compile
clang hello.c -o hello

# With warnings and optimization
clang -Wall -Wextra -O2 program.c -o program

# Debug build
clang -g -O0 program.c -o program

# C++ compilation
clang++ -std=c++20 program.cpp -o program

# With sanitizers
clang -fsanitize=address -g program.c -o program

# Multiple source files
clang main.c utils.c -o program

# Link with library
clang program.c -o program -lm -lpthread

SANITIZERS

Address Sanitizer:

Detect memory errors

Thread Sanitizer:

Detect data races

Undefined Behavior Sanitizer:

Detect undefined behavior

Memory Sanitizer:

Detect uninitialized memory reads

CAVEATS

Some GCC-specific features not supported. Different optimization behavior than GCC. Sanitizers add overhead. Error messages more verbose than some prefer. Compilation may be slower than GCC in some cases.

HISTORY

clang was created by Apple and the LLVM community starting in 2007 as a modern, modular compiler to replace GCC, first released in 2009.