Makefiles

If you have many source files you don't need to recompile them all if you only change one of them. By writing a makefile that describes how the executable is produced from the source files, the make command will do all the work for you. In the 1A/1B courses makefiles were created by the xcc program, but you may well need to write your own eventually.

The following makefile says that pgm depends on two files a.o and b.o, and that they in turn depend on their corresponding source files (a.cc and b.cc) and a common file incl.h:

   pgm: a.o b.o
       aCC a.o b.o -o pgm
   a.o: incl.h a.cc
       aCC -Aa -c a.cc
   b.o: incl.h b.cc
       aCC -Aa -c b.cc

Lines with a `:' are of the form

target : dependencies

make updates a target only if it's older than a file it depends on. The way that the target should be updated is described on the line following the dependency line (Note: this line needs to begin with a TAB character).

Here's a more complex example of a makefile for a program called dtree. First some variables are created and assigned. In this case typing `make' will attempt to recompile the dtree program (because the default target is the first target mentioned). If any of the object files it depends on are older than their corresponding source file, then these object files are recreated.

The targets needn't be programs. In this example, typing `make clean' will remove any files created during the compilation process.

# Makefile for dtree
DEFS =  -O2 -DSYSV
CFLAGS = $(DEFS) -O
LDFLAGS = 
CC = aCC
LIBS = -lmalloc -lXm -lXt -lX11 -lm

BINDIR = /usr/local/bin/X11
MANDIR = /usr/local/man/man1

OBJECTS_A = dtree.o Arc.o Graph.o 	#using XmGraph

ARCH_FILES = dtree.1 dtree.cc Makefile Dtree Tree.h TreeP.h \
   dtree-i.h Tree.cc Arc.cc Arc.h ArcP.h Graph.cc Graph.h GraphP.h

dtree: $(OBJECTS_A)
        $(CC) -o dtree $(LDFLAGS) $(OBJECTS_A) $(LIBS)

Arc.o:	Arc.cc
        $(CC) -c $(CFLAGS) Arc.cc

Graph.o:	Graph.cc
        $(CC) -c $(CFLAGS) Graph.cc

dtree.o:	dtree.cc
        $(CC) -o dtree.o -c $(CFLAGS) -DTREE dtree.cc

install: dtree dtree.1
        cp dtree $(BINDIR)
        cp dtree.1 $(MANDIR)

clean:
        rm -f dtree *.o core tags a.out