A tutorial for Makefile
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http://oucsace.cs.ohiou.edu/~bhumphre/makefile.html
Makefile Getting Started
What is Make?
Make is a program that looks for a file called "makefile" or"Makefile", within the makefile are variables and things calleddependencies. There are many things you can do with makefiles, if allyou've ever done with makefiles is compile C or C++ then you aremissing out. Pretty much anything that needs to be compiled(postscript, java, Fortran), can utilize makefiles.Format of Makefiles -- Variables
First, lets talk about the simpler of the two ideas in makefiles,variables. Variable definitions are in the following format:VARNAME = ValueSo lets say i want to use a variable to set what compiler i'm going touse. This is helpful b/c you may want to switch from cc to gcc or tog++. We would have the following line in our makefile
CC = gccthis assigns the variable CC to the string "gcc". To expandvariables, use the following form:
${VARNAME}So to expand our CC variable we would say:
${CC}
Format of Makefiles -- Dependencies
Dependencies are the heart of makefiles. Without them nothing wouldwork. Dependencies have the following form:dependecy1: dependencyA dependencyB ... dependencyN command for dependency1
Very Important:
The commands underneath the dependencies must have a tab before them.This lets make know it is a command and not some kind of crazydependency.So how do we read what was just written above? Dependency1 isdependent upon dependencyA, and dependencyB, up to however manydependencies you have. The program make, looks at dependency1 andsees it is dependent upon dependencyA, so then it looks later in themakefile for how dependencyA is defined. Lets make a sample makefile:
myprogram: mainprog.cc myclass.cc gcc mainprog.cc myclass.ccThat is probably one of the simplest makefiles that could be made.When you type make, it automatically knows you want to compile the'myprogram' dependency (because it is the first dependency it found inthe makefile). It then looks at mainprog.cc and sees when the lasttime you changed it, if it has been updated since last you typed'make' then it will run the 'gcc mainprog.cc ..." line. If not, thenit will look at myclass.cc, if it has been edited then it will executethe 'gcc mainprog.cc ..." line, otherwise it will not do anything forthis rule.
Another example might be easier to see for dependencies, lets say youhave a class, and more than one file depends upon objects of thatclass type. Then it makes sense to create a .o file of that class andcompile it in with the file. Here is a sample of what I'm talkingabout
myprogram: mainprog.cc subfile1.o myclass.o gcc mainprog.cc subfile1.o myclass.osubfile1.o: subfile1.cc myclass.o gcc -c mainprog.cc subfile1.o myclass.omyclass.o: myclass.cc gcc -c myclass.ccNotice the dependencies here, when 'make' is run, the dependencycalled "myprogram" is run first, and then the dependency subfile1.o isfound, and then the myclass.o dependency is foudn withint subfile1.o.So myclass.cc is compiled, then subfile1.o is compiled, then we arefinally back up to the myprogram dependency. Finally all threedependencies are compiled in to create a.out.
Tying variables and dependencies together
You can use variables within your dependencies very easily. Lets takethat last example, and use two variables, one for the compiler we aregoing to use, and another for the options to that compiler. Thismakes life a lot simpler if say we want to turn off debugging for allthe code, or turn it on, whichever is preferred. Here is an exampletying it together.COMPILER = gccCCFLAGS = -gmyprogram: mainprog.cc subfile1.o myclass.o ${COMPILER} ${CCFLAGS} mainprog.cc subfile1.o myclass.osubfile1.o: subfile1.cc myclass.o ${COMPILER} ${CCFLAGS} -c mainprog.cc subfile1.o myclass.omyclass.o: myclass.cc ${COMPILER} ${CCFLAGS} -c myclass.ccnotice how clean this is? It is easy to add extra options andlibraries to your compiler if need be. Life is a whole lot simplerwith makefiles, for a final addition to our makefile lets makesomething that cleans out all our code, starting with what we hadbefore, we simply add a new dependency, named "clean". The additiongoes as follows:
COMPILER = gccCCFLAGS = -gmyprogram: mainprog.cc subfile1.o myclass.o ${COMPILER} ${CCFLAGS} mainprog.cc subfile1.o myclass.osubfile1.o: subfile1.cc myclass.o ${COMPILER} ${CCFLAGS} -c mainprog.cc subfile1.o myclass.omyclass.o: myclass.cc ${COMPILER} ${CCFLAGS} -c myclass.ccclean: rm -rf *.o a.outSo when we type 'make clean' at the command line, it will remove allour .o files and the executable that we have.
Conclusions
Makefiles are very very helpful when dealing with projects. The firstthing you should do when making a project is create a makefile, itmakes your life a lot easier. They are very powerful things, if youhave any questions feel free to email me atbhumphre@cs.ohiou.edu have fun!Last modified: Mon Oct 16 13:21:58 EDT 2000
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