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Lesson 12 — Non-Recursive Make

What you'll learn

How to use a single top-level Makefile that includes fragments from each subdirectory, giving Make a complete dependency graph.

The problem with recursive Make

In lesson 11, Make runs as separate processes in each directory. It can't see dependencies across boundaries. With -j4, it might start building app before libmath finishes.

The paper "Recursive Make Considered Harmful" (Peter Miller, 1998) describes this in detail.

The solution: include

Instead of invoking sub-Makes, a single Makefile includes module fragments (module.mk) from each directory:

12_nonrecursive_make/
├── Makefile                ← single top-level Makefile
├── libfmt/
│   ├── module.mk           ← defines LIBFMT_SRCS, LIBFMT_OBJS, etc.
│   ├── include/fmt.hpp
│   └── src/fmt.cpp
└── app/
    ├── module.mk           ← defines APP_SRCS, APP_OBJS, etc.
    └── src/main.cpp

Each module.mk uses full paths relative to the project root:

# libfmt/module.mk
LIBFMT_SRCS = libfmt/src/fmt.cpp
LIBFMT_OBJS = $(LIBFMT_SRCS:.cpp=.o)
LIBFMT_LIB  = libfmt/libfmt.a

$(LIBFMT_LIB): $(LIBFMT_OBJS)
	$(AR) $(ARFLAGS) $@ $^

Critical detail: declare all before includes

# Declare default target BEFORE includes
all:

include libfmt/module.mk
include app/module.mk

# Wire the dependency after all variables are defined
all: $(APP_BIN)

Without this, the first target inside a module.mk becomes Make's default target — not what you want.

Advantages over recursive Make

Recursive Non-recursive
Multiple Make processes Single Make process
Manual ordering required Make resolves order from dependency graph
-j can break across modules -j works correctly everywhere
Can't detect cross-module changes Full dependency visibility

Try it

cd 12_nonrecursive_make
make            # builds library and app in correct order
./app/app       # bold, underlined, and red text (ANSI codes)
make -j4        # parallel build — works correctly!
make clean

Files

File Purpose
Makefile Top-level: sets variables, includes fragments
libfmt/module.mk Defines library targets and sources
libfmt/include/fmt.hpp ANSI terminal formatting functions
libfmt/src/fmt.cpp Implements bold, underline, red
app/module.mk Defines app target and sources
app/src/main.cpp Uses the formatting library