Header Files & Multiple Translation Units

A translation unit is a source file after preprocessing. Splitting a project into multiple .c files improves modularity.

Typical layout:

project/
├─ src/
│   ├─ main.c          // contains main()
│   └─ utils.c         // implementation of utility functions
├─ include/
│   └─ utils.h         // declarations for utils.c
├─ Makefile
└─ README.md

utils.h provides function prototypes and type definitions. utils.c includes the header and defines the functions. The compiler compiles each .c file separately, then the linker combines the object files.

---

⚡ Build with gcc

gcc -Iinclude -c src/utils.c   # produces utils.o
gcc -Iinclude -c src/main.c    # produces main.o
gcc -o myprogram main.o utils.o

---

📦 Using a Makefile

CC=gcc
CFLAGS=-Wall -Wextra -Iinclude
OBJ=main.o utils.o

myprogram: $(OBJ)
	$(CC) -o $@ $^

%.o: src/%.c
	$(CC) $(CFLAGS) -c $< -o $@

clean:
	rm -f $(OBJ) myprogram