GNU autotools primer (part ...

We'll start off with a very simple Hello World program, in plain C:

#include <stdio.h>

int main(int argc,char **argv) {

printf("Hello world\n");

}

Create a directory called hello and within that, a subdirectory called src:

mkdir -p hello/src

The topmost directory, hello will contain the entire package, and src will be where we place the source code. So now, take the snippet of c-code above, and save it in the file hello/src/hello.c.





automake uses templates with the name Makefile.am to build Makefile.in templates for autoconf to process. You will need to create a Makefile.am file within every directory in your package that automake will perform its work in. So, for this example, create the following files.

hello/src/Makefile.am:

bin_PROGRAMS = hello

hello_SOURCES = hello.c

Some explanation is required here. Automake rules take the form of target_primary. So, above, where we have the rule bin_PROGRAMS, we are specifying the list of programs that we are building that will be played in the bin directory, when installed. Similarly, we could have used sbin_PROGRAMS for any programs that we were building that we wish to place in the sbin directory.

The PROGRAMS primary will then look for source files from which it can be built. Since our target program is called hello, we specify a list of sources (separated by spaces; in the above example, we only have the one source file, hello.c) using the target hello_SOURCES.

hello/Makefile.am:

SUBDIRS = src

SUBDIRS is a special variable that lists all of the subdirectories that automake must process. If you were to have any subdirectories underneath hello/src, then you'd also include a SUBDIRS line in your hello/src/Makefile.am file, listing each of them.

Now, create hello/configure.ac with the following contents:

AC_INIT([hello],[0.0.1])

AM_INIT_AUTOMAKE

AC_PROG_CC

AC_OUTPUT([
Makefile
src/Makefile
])

configure.ac is autoconf's primary configuration file, which uses the M4 macro processing language. We'll start looking at each of these directives from the top. AC_INIT must always be the first directive called; here, we've used two arguments - the name of the package (in this case hello), and the version number (0.0.1).

AM_INIT_AUTOMAKE is used only when you're using automake with autoconf; it takes one argument (options to run automake with), but in this case we haven't supplied any. If we wanted to cause all warnings to make it abort, we could have put: AM_INIT_AUTOMAKE([-Werror]).

AC_PROG_CC is a macro that tells configure to look for a C compiler. When run, it will first look at the contents of the CC environment variable, and if this is empty, it will test for the presence of gcc and then fall back to cc if necessary. Should you wish autoconf to test for the presence of a C++ compiler, use AC_PROG_CXX.

The final statement, AC_OUTPUT lists the files that the configure script should create when it is run; in this case, two Makefiles, one in each directory. This should always be the last directive in the configure.ac file.