我如何为 GMP 项目制作 Makefile

Question

I have a problem while attempting to generate a Makefile for my C project. It contains 3 files alea.c crypto.c and main.c. Here is my Makefile:

SHELL = /bin/bash
CC = gcc
RM = rm -rf
TAR = tar
MKDIR = mkdir
CHMOD = chmod
CP = cp
MV = mv

PROGNAME = Crypto_ivsk
EXEC = Crypt
PACKAGE = $(PROGNAME)
VERSION = 0.3
DISTDIR = $(PACKAGE)-$(VERSION)
HEADERS = alea.h crypto.h  gmp.h
SOURCES = alea.c crypto.c main.c 

LDFLAGS = -lgmp 
CFLAGS = -Wall

OBJ = $(SOURCES:.c=.o) 
DISTFILES = $(SOURCES) Makefile $(HEADERS) 

all: $(EXEC)  

$(EXEC): $(OBJ)  
    $(CC) $(OBJ) -o $(LDFLAGS) $(EXEC)

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

dist: distdir
    $(CHMOD) -R a+r $(DISTDIR)
    $(TAR) zcvf $(DISTDIR).tar.gz $(DISTDIR)
    $(RM) $(DISTDIR)

distdir: $(DISTFILES)
    $(RM) $(DISTDIR)
    $(MKDIR) $(DISTDIR)
    $(CHMOD) 777 $(DISTDIR)
    $(CP) -rf $(DISTFILES) $(DISTDIR)
clean:
    $(RM) $(PROGNAME) $(OBJ) *~ $(DISTDIR).tar.gz

but when i type "make" in my shell the following error appears: "no rule to make target gmp.h needed by alea.o STOP"

I can't do anything about this with my low level, can someone please help me?

Thank you:)

Answer 1

You have said that all your %.o files depend of the file of same name with extension .c and from the header files they include.

You have put gmp.h as an include in this directory that make does not find (I imagine you refer to the GNU Multiprecision library include file) which is a file you should not put in your $(HEADER) variable. Why?

Very simple, because you are never going to change that file, so the files dependent of it have to be recompiled, as it is a system file.

There are some recommendations I'm givin to you to avoid problems in the future.

• Don't define variables you are not going to use, or variables you don't plan to change. Variables work in make as constants. You define them in a single place, but you repeat them here and there on your Makefile . These are the candidates to use.

• make has a bunch of already defined rules (indeed, the rule to build an object .o file from a .c file is already included in almost any of the make implementations actually in use. So you have better to respect the already installed rule, than provide you yours, because this rule is normally adapted to your system, and the Makefile contents is more portable.

• The same applies to variables that represent system programs, like CC , RM , LEX , YACC , etc. Normally, one redefines it when the program has special compilation needs (which is not your case)

• You have an error in the final link phase of your makefile as you specify options -o $(LDFLAGS) $(EXEC) to the linker, while it should be $(LDFLAGS) -o $(EXEC) (better if you put $(LDFLAGS) first, as the linking options will be applied once all object files have been processed)

With this premises, this is the suggested Makefile for your project.

PACKAGE   = Crypto_ivsk
VERSION   = 0.3
DISTNAME = $(PACKAGE)-$(VERSION)

# don_t include system headers, because 1) you are never to
# modify them and 2) because they are in a different
# directory and make will not find them, and then it will
# try to create them in the local dir, if you put any in a
# dependency rule.
headers   = alea.h cripto.h main.h

# This variable is understood by the C source compilation rule.
CFLAGS = -Wall

# targets holds the list of programs we are to build.
targets   = Crypt

# toclean is a variable we initialize to the programs we are
# to build and for each program we add all the objects we
# compile of it.
toclean   = $(targets)

# put here programs that must be built before linking Crypt,
# e.g. program resource files, that are not used in the linking.  In this case we have none.
Crypt_deps =

# Put here things that must be built before linking Crypt,
# e.g. object files, that ***are*** used to link it.
Crypt_objs = alea.o cripto.o main.o

# Place for the libraries to build Crypt.
Crypt_libs = -lgmp

# For each program we add to toclean the object files that
# compose it, so we can erase just doing $(RM) $(toclean)
# Pay special attention to the += operator.
toclean += $(Crypt_objs)

# If we have more programs to build, add (prefixed) groups 
# of variables like the above.

DISTFILES = $(Cryp_objs:.o=.c) Makefile $(headers) 

# all should be a .PHONY target.
.PHONY: all clean dist

all: $(targets)
    @echo Build finished at: `date`

# repeat this for each file in $(targets)
# $@ is the target of the rule
Crypt: $(Crypt_deps) $(Crypt_objs)
    $(CC) $(LDFLAGS) $(Crypt_ldfl) -o $@ $(Crypt_objs) $(Crypt_libs)

dist: $(DISTNAME).tar.gz

# we link the files in $(DISTFILES) so we don_t consume
# disk space with the copies.
$(DISTNAME).tar.gz: $(DISTFILES)
    mkdir $(DISTNAME)
    ln $(DISTFILES) $(DISTNAME)/.
    tar cvfz $@ $(DISTNAME)
    $(RM) $(DISTNAME)

# this cleans everything built.
clean:
    $(RM) $(toclean)

# this can be written as
# alea.o cripto.o main.o: $(headers)
# but in case they include different lists of header is
# better to put it this way.
alea.o: $(headers)
cripto.o: $(headers)
main.o: $(headers)

This Makefile schema will give you better results, and it is easily extensible to build several programs or libraries.

As you see, there's no compilation rule for the sources to object files. This is because there's a builtin rule in make . There's also a default definition for RM (in GNU make ) and for CC .

It's important that you don't redefine CC to gcc , as your code will be more portable if you don't force everybody to build your program with gcc .

In any case, if you use optional assignments,

CFLAGS       ?= -O -Wall -std=c98 -pedantic

instead, then you'll allow the builder to specify a different value for CFLAGS in the command line (or through the environment) and your script will be more flexible.