Monday, January 12, 2015

Makefiles Made Easy

The bane of computer programming is the Makefile. As soon as there are more than one source file and a library, a Makefile becomes essential and generating one can be painful.  The Makefile syntax reminds me of a sendmail configuration file, which looks like someone banged his head on a keyboard:

# This rule ensures that all local mail is delivered using the 
# smtp transport, everything else will go via the smart host. 
R$* < @ $* .$m. > $* $#smtp $@ $2.$m. $: $1 < @ $2.$m. > $3 dnl


Way back in the dark ages, before there was m4, I actually edited a few sendmail files by hand - that was how I earned my UNIX beard - but good grief...

Same as with sendmail, you should never edit a Makefile manually these days.  It is a total waste of time.  There now are nice and simple utilities to do it for you!


GCC -MM

If you have a very simple project, then gcc can generate the Makefile for you:
$ gcc -MM *.c > Makefile
$ make

Error: cc1plus

If you get the following or similar error regarding cc1plus, then the solution is not at all obvious:
gcc: error trying to exec 'cc1plus': execvp: No such file or directory

The problem is that while gcc is installed, g++ is missing:
# yum install gcc-c++

Also see the previous post for details on installing gcc.

CMake

If your project is more complex, then cmake can generate the Makefile for you, but you need to give it a few instructions in the file CMakeLists.txt.  First install cmake and related tools:
# yum install cmake*

Now create the file CMakeLists.txt and tell it which are the output, source and libraries:
project(FlashProject)
cmake_minimum_required(VERSION 2.8.12.2)
add_executable(flasher flasher.c)
find_library(FTDI ftdi)
target_link_libraries(flasher ${FTDI})

Note that gcc assumes that library file names start with lib and end with .so, therefore only specify the base ftdi or whatever, not libftdi.so.

The first time you run cmake, you need to specify the compiler:
$ CXX=gcc
$ export CXX

After that, run cmake to generate the makefile complete with all the obscure, head banging, gobbledygook lines:
$ cmake .
-- Configuring done
-- Generating done
-- Build files have been written to: /home/herman/sw/ftdi


Now you should have a very detailed almost 200 line Makefile and can compile your project with:
$ make

La voila!


No comments:

Post a Comment

On topic comments are welcome. Junk will be deleted.