Red Antigua - C tutorials - Autotools

The previous example showed an example of a hand-crafted layout template for configure.ac.
The layout template can be created automatically by another autotool, autoscan.
Just type the following in an empty directory:

autoscan

You should now have 2 files in the current directory:

$ ls
autoscan.log  configure.scan

As we see, the contents of the generated configure.scan is similar to our hand-crafted template:

#                                               -*- Autoconf -*-
# Process this file with autoconf to produce a configure script.

AC_PREREQ(2.56)
AC_INIT(FULL-PACKAGE-NAME, VERSION, BUG-REPORT-ADDRESS)

# Checks for programs.

# Checks for libraries.

# Checks for header files.

# Checks for typedefs, structures, and compiler characteristics.

# Checks for library functions.

AC_OUTPUT

As the name autoscan implies, you can guess that it can do other things as well, not only create empty configure.ac templates.
As explained in the autoconf manual: Using autoscan to Create configure.ac:

"It (autoscan) searches the source files for common portability problems and creates a file configure.scan which is a preliminary configure.ac..."

Let test the source code search feature of autoscan with a small program.
Create the following two files in the same directory as configure.scan:

sleep.h

#include <stdio.h>
#include <unistd.h>          /* Needed for sleep() */

sleep.c

#include "sleep.h"

#define SECONDS_TO_SLEEP 3

int
main()
{
    unsigned int sleep_left = 0;
    /* sleep() for SECONDS_TO_SLEEP seconds, then print a message. */
    sleep(SECONDS_TO_SLEEP);
    printf("I woke up after %d seconds.\n", SECONDS_TO_SLEEP);
    return 0;
}

Remove earlier created files, repeat autoscan and check the contents of configure.scan:

rm -f autoscan.log configure.scan && autoscan && cat configure.scan

configure.scan

#                                               -*- Autoconf -*-
# Process this file with autoconf to produce a configure script.

AC_PREREQ(2.56)
AC_INIT(FULL-PACKAGE-NAME, VERSION, BUG-REPORT-ADDRESS)
AC_CONFIG_SRCDIR([sleep.c])
AC_CONFIG_HEADER([config.h])

# Checks for programs.
AC_PROG_CC

# Checks for libraries.

# Checks for header files.
AC_CHECK_HEADERS([unistd.h])

# Checks for typedefs, structures, and compiler characteristics.

# Checks for library functions.
AC_OUTPUT

As we see, autoscan detected our source file sleep.c and added the following macros:

AC_CONFIG_SRCDIR:

some file that is in the package's source directory.

AC_CONFIG_HEADER:

containing C preprocessor #define statements.

AC_PROG_CC:

determine a C compiler to use.

AC_CHECK_HEADERS:

check for existing header file(s) (in our case only one, unistd.h).

To get a very basic, but working input file to autoconf, rename configure.scan to configure.ac...

mv configure.scan configure.ac

... and update the AC_INIT macro, and add the AC_COPYRIGHT macro:

configure.ac

#                                               -*- Autoconf -*-
# Process this file with autoconf to produce a configure script.

AC_PREREQ(2.56)
AC_INIT(sleep, 0.0.1, me@example.com)
AC_CONFIG_SRCDIR([sleep.c])
AC_CONFIG_HEADER([config.h])
AC_COPYRIGHT([Copyright 2007, Johan Kuuse])

# Checks for programs.
AC_PROG_CC

# Checks for libraries.

# Checks for header files.
AC_CHECK_HEADERS([unistd.h])

# Checks for typedefs, structures, and compiler characteristics.

# Checks for library functions.
AC_OUTPUT

Run autoconf to create configure:

autoconf

Run the configure script, just to test the AC_INIT and AC_COPYRIGHT macros:

./configure --version

You should see something similar to:

sleep configure 0.0.1
generated by GNU Autoconf 2.56

Copyright 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001, 2002
Free Software Foundation, Inc.
This configure script is free software; the Free Software Foundation
gives unlimited permission to copy, distribute and modify it.

Copyright 2007, Johan Kuuse

To display the bug report mail address:

./configure --help|tail -1

Should display:

Report bugs to <me@example.com>

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Last modified: Tue Oct 23 15:41:00 Romance Daylight Time 2007