On "makefiles"

[Roman]

Hey,

I noticed that in the whirlwind tour, it is mentioned that makefiles should be created for every program you compile.
What exactly is a makefile? I did a quick wikipedia search, and it seems that it's something like instructions on how to compile the program (?), but that it is done automatically in modern compilers. The textbook we're using (C Programming, A modern Approach by K.N. King) does not mention makefiles until later on, when it discusses building multiple-file programs. Is it better to make makefiles for smaller programs as well? Or is it a skill best left for somewhat later?

Thanks in advance,
-RZ

[jernst]

Makefiles give some automation to compiling your projects, its especially helpful when you have to compile and link together many files. You set up some "targets" which are sort of rules and options on how to compile particular files or groups of files in your project. In these rules you can set which compiler you want to use and pass any arguments you want to the compiler. Then you can type make and if your Makefile is set up properly, it will compile everything. It saves you from having to type in "gcc/g++ filename -options" etc... to compile. Its also useful if you are working on things with other people, or are distributing the source since the others might not be familiar with what is required for your code to compile.

[Clayton]

To put simply, and with a trivial example, it's the difference between:

code:

>> gcc -o foo foo.c foo2.c foo3.c

multiple times, or the above once (more or less), and then just:

code:

>> make

every time you wish to compile your code afterwards. Obviously the benefits are more as the size of a project increases, but it's still a good idea to get into the habit of having a makefile for each project you write.

[wtd]

Also handy is a good "clean" rule. Any decently large project will be built about a bajillion times, and while compiling everything manually every time might not be awful, cleaning up the generated files in between would be.

[btiffin]

I think everyone is missing one the key reasons for the invention of make and Makefile. Dependency graphs.
A simple build script for

code:

$ gcc -o foo foo.c foo2.c foo3.c

is trivial. But what if foo2.c and foo3.c rarely change? make is smart enough to not recompile foo2 and foo3 by comparing the modification times. Without that feature, I doubt make would have ever been developed in the first place.

On a GNU/Linux box with build-essentials installed, you can try make without a Makefile. GNU make has default rules that know how to create executables when it sees a .c file. So for simple things; just type $ make filename. For more complex things, dig in and create the dependency list in a Makefile. Then life is sweet.

After that, get used to automake, autoconf, and libtool and most of the crap involved with POSIX enabled cross-platform issues are taken care of for you and you'll look and feel like a real pro.

Cheers

[OneOffDriveByPoster]

btiffin @ Fri Jan 16, 2009 1:23 pm wrote:

After that, get used to automake, autoconf, and libtool and most of the crap involved with POSIX enabled cross-platform issues are taken care of for you and you'll look and feel like a real pro.

What? You mean my strictly conforming POSIX application will not work on all POSIX implementations?

[Zeroth]

OneOffDriveByPoster @ Fri Jan 16, 2009 12:32 pm wrote:

btiffin @ Fri Jan 16, 2009 1:23 pm wrote:

After that, get used to automake, autoconf, and libtool and most of the crap involved with POSIX enabled cross-platform issues are taken care of for you and you'll look and feel like a real pro.

What? You mean my strictly conforming POSIX application will not work on all POSIX implementations?

They may "conform", but the POSIX implementation doesn't define where the more recent kinds of apps store their configuration settings... ie, X and beyond! It also doesn't define access standards for different directories, so what works on say Linux won't on FreeBSD because the access settings are different.

[btiffin]

By the way; I'm relatively new to automake myself, but became a fan with the first Makefile.in. The auto generated targets are a boon.

It's a fair load of crap to read through the first time, but after that ... Smooth.

Comes with the Old Guy ramble on recommendation.

Cheers

[jain.rani]

A makefile is the set of instructions that you use to tell makepp how to build your program. Makepp can accept most makefiles written for the standard unix make, but if you're starting from scratch, it is often much simpler to use some of makepp's advanced features. This is an introduction for writing makefiles that are specific to makepp.


A simple makefile

Suppose you are writing a C++ program which has two source modules, processing.cxx and gui.cxx, along with numerous include files. If you were to build your program from scratch, you would need to execute something like these commands:

c++ -c processing.cxx -o processing.o
c++ -c gui.cxx -o gui.o
c++ processing.o gui.o -o my_program


Thanks
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