An example makefile
As mentioned, the code-extraction tool
ExtractCode.cpp automatically generates makefiles for each
chapter. Because of this, the makefiles for each chapter will not be
placed in the book (all the makefiles are packaged with the source code, which
you can download from www.BruceEckel.com). However, it’s
useful to see an example of a makefile. What follows is a shortened
version of the one that was automatically generated for this chapter by the
book’s extraction tool. You’ll find more than one makefile in
each subdirectory (they have different names; you invoke a specific one with
‘make -f’). This one is for GNU C++:
CPP = g++
OFLAG = -o
.SUFFIXES : .o .cpp .c
.cpp.o :
$(CPP) $(CPPFLAGS) -c $<
.c.o :
$(CPP) $(CPPFLAGS) -c $<
all: \
Return \
Declare \
Ifthen \
Guess \
Guess2
# Rest of the files for this chapter not shown
Return: Return.o
$(CPP) $(OFLAG)Return Return.o
Declare: Declare.o
$(CPP) $(OFLAG)Declare Declare.o
Ifthen: Ifthen.o
$(CPP) $(OFLAG)Ifthen Ifthen.o
Guess: Guess.o
$(CPP) $(OFLAG)Guess Guess.o
Guess2: Guess2.o
$(CPP) $(OFLAG)Guess2 Guess2.o
Return.o: Return.cpp
Declare.o: Declare.cpp
Ifthen.o: Ifthen.cpp
Guess.o: Guess.cpp
Guess2.o: Guess2.cpp
The macro CPP is set to the name of the
compiler. To use a different compiler, you can either edit the makefile
or change the value of the macro on the command line, like
this:
make CPP=cpp
Note, however, that
ExtractCode.cpp has an automatic scheme to automatically build
makefiles for additional compilers.
The second macro OFLAG is the flag
that’s used to indicate the name of the output file. Although many
compilers automatically assume the output file has the same base name as the
input file, others don’t (such as Linux/Unix compilers, which default to
creating a file called a.out).
You can see that there are two suffix
rules here, one for cpp files and one for .c files (in case any C
source code needs to be compiled). The default target is all, and each
line for this target is “continued” by using the backslash, up until
Guess2, which is the last one in the list and thus has no backslash.
There are many more files in this chapter, but only these are shown here for the
sake of brevity.
The suffix rules take care of creating
object files (with a .o extension) from cpp files, but in general
you need to explicitly state rules for creating the executable, because normally
an executable is created by linking many different object files and make
cannot guess what those are. Also, in this case (Linux/Unix) there is no
standard extension for executables so a suffix rule won’t work for these
simple situations. Thus, you see all the rules for building the final
executables explicitly stated.
This makefile takes the absolute
safest route of using as few make features as possible; it only uses the
basic make concepts of targets and dependencies, as well as macros. This
way it is virtually assured of working with as many make programs as
possible. It tends to produce a larger makefile, but that’s not so
bad since it’s automatically generated by
ExtractCode.cpp.
There are lots of other make
features that this book will not use, as well as newer and cleverer versions and
variations of make with advanced shortcuts that can save a lot of time.
Your local documentation may describe the further features of your particular
make, and you can learn more about make from Managing Projects
with Make by Oram and Talbott (O’Reilly, 1993). Also, if your compiler
vendor does not supply a make or it uses a non-standard make, you
can find GNU make for virtually any platform in existence by searching the
Internet for GNU archives (of which there are
many).
