cheatsheet/cpp-cheatsheet.md

C++ with Clang & Make — Cheat Sheet

Writing C++

A basic C++ file (hello.cpp):

#include <iostream>

int main() {
    std::cout << "Hello, world!" << std::endl;
    return 0;
}

Compiling with Clang

Command	What it does	Example
clang++	Compile to an executable named a.out	clang++ hello.cpp
clang++ -o	Compile and name the output	clang++ hello.cpp -o hello
clang++ -Wall	Enable all warnings (always use this!)	clang++ -Wall hello.cpp -o hello
clang++ -std=c++17	Use a specific C++ version	clang++ -std=c++20 -Wall prog.cpp -o prog
clang++ -g	Include debug info (for use with a debugger)	clang++ -g -Wall hello.cpp -o hello

Common flags explained:

Flag	Meaning
-o	Output filename (instead of a.out)
-Wall	Enable most compiler warnings
-Wextra	Enable even more warnings
-std=c++17	Use C++17 standard (also c++11, c++14, c++20)
-g	Include debug symbols (for gdb or lldb)
-O2	Optimize for speed

Full compile example

clang++ -Wall -Wextra -std=c++20 my_program.cpp -o my_program
./my_program

Running Your Program

./my_program          # Run it
./my_program arg1     # Pass a command-line argument

Make & Makefiles

make automates your build so you don't have to type long clang++ commands.

Example project structure

project/
├── Makefile
├── main.cpp
├── helpers.cpp
└── helpers.hpp

Minimal Makefile

hello: hello.cpp
    clang++ -Wall -std=c++17 hello.cpp -o hello

⚠️ The indented line must use a Tab, not spaces.

Building with make

make        # Build the first target
make hello  # Build the target named 'hello'

Better Makefile with variables

CXX     = clang++
CXXFLAGS = -Wall -Wextra -std=c++20
TARGET   = my_program

$(TARGET): main.cpp helpers.cpp helpers.hpp
    $(CXX) $(CXXFLAGS) main.cpp helpers.cpp -o $(TARGET)

clean:
    rm -f $(TARGET)

.PHONY: clean

Command	What it does
make	Build the program
make clean	Delete the compiled program
make -j4	Build using 4 CPU cores (faster)

Typical Makefile with separate compilation

CXX       = clang++
CXXFLAGS  = -Wall -Wextra -std=c++20
TARGET    = my_program
OBJECTS   = main.o helpers.o

$(TARGET): $(OBJECTS)
    $(CXX) $(OBJECTS) -o $(TARGET)

main.o: main.cpp helpers.hpp
    $(CXX) $(CXXFLAGS) -c main.cpp -o main.o

helpers.o: helpers.cpp helpers.hpp
    $(CXX) $(CXXFLAGS) -c helpers.cpp -o helpers.o

clean:
    rm -f $(TARGET) $(OBJECTS)

.PHONY: clean

Quick Reference — Common Workflow

# 1. Write your code
nano hello.cpp

# 2. Compile
clang++ -Wall -std=c++20 hello.cpp -o hello

# 3. Run
./hello

# Or use a Makefile
make
./hello

Tips

• Always compile with -Wall — warnings catch bugs!
• Use -std=c++20 to get modern C++ features (auto, ranges, std::span, etc.)
• If clang++ isn't installed: sudo apt install clang
• If make isn't installed: sudo apt install make
• When editing Makefiles: rules must be indented with a Tab character