2014-1-5 Makefile tips

Makefile working tips. Usual simple makefile
looks like this:

make:
	gcc main.c -o main

but when your project grows and you use more files it becomes
like this:

make:
	gcc -O2 -c file1.c
	gcc -O2 -c file2.c
	gcc -O2 -c file3.c
	gcc -O2 main.c file1.o file2.o file3.o -o main

This is standard growth of file. Its better practice to
reuse your code, it could applied to your makefile also.

When you have few small project and you want simply copy
makefile and it works.

1. Compiler name
Usually everyone prefer one compiler. And time to time only
check if code compiles with other compilers.

CC=gcc
make:
	$(CC) -O2 -c file1.c
	$(CC) -O2 -c file2.c
	$(CC) -O2 -c file3.c
	$(CC) -O2 main.c file1.o file2.o file3.o -o main

2. Project name
Every project have unique name and you also would like
to change it if there is need.

PROJECT=project
CC=gcc
make:
	$(CC) -O2 -c file1.c
	$(CC) -O2 -c file2.c
	$(CC) -O2 -c file3.c
	$(CC) -O2 main.c file1.o file2.o file3.o -o $(PROJECT)

3. Compiler flags
Usual problem is when some compiling flags causes problems
and you need to change every single entry in file.

PROJECT=project
CC=gcc
CFLAGS=-O2
make:
	$(CC) $(CFLAGS) -c file1.c
	$(CC) $(CFLAGS) -c file2.c
	$(CC) $(CFLAGS) -c file3.c
	$(CC) $(CFLAGS) main.c file1.o file2.o file3.o -o $(PROJECT)

This 3 variables reduce how number of places that you need
to edit if something changes.

Next thing is to fix problem when you need to add or remove
file from project and after that you have manually to edit
at least 2 lined in makefile.

4. Use multiple files

One of they ways how to reduce number of files edited is to add
new variable where all files is listed:

PROJECT=project
CC=gcc
CFLAGS=-O2
SOURCES=file1.c file2.c file3.c
OBJECTS=$(SOURCES:.c=.o)

all: $(OBJECTS) $(PROJECT)

$(PROJECT): $(SOURCES) main.c
	$(CC) $(OBJECTS) $(CFLAGS) main.c -o $(PROJECT)

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

Here was added file auto-matching for *.c files to make them *.o

5. Auto matching C files

Last thing to add is auto match all *.c in directory.

PROJECT=project
CC=gcc
CFLAGS=-O2
SOURCES=$(wildcard *.c)
OBJECTS=$(SOURCES:.c=.o)

all: $(OBJECTS) $(PROJECT)

$(PROJECT): $(SOURCES) main.c
	$(CC) $(OBJECTS) $(CFLAGS) -o $(PROJECT)

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

Now project makefile can be easily copied and with
changing only one variable value everything should be OK
To run any makefile:

make -f makefile_name.mk