Follow Techotopia on Twitter

On-line Guides
All Guides
eBook Store
iOS / Android
Linux for Beginners
Office Productivity
Linux Installation
Linux Security
Linux Utilities
Linux Virtualization
Linux Kernel
System/Network Admin
Programming
Scripting Languages
Development Tools
Web Development
GUI Toolkits/Desktop
Databases
Mail Systems
openSolaris
Eclipse Documentation
Techotopia.com
Virtuatopia.com

How To Guides
Virtualization
General System Admin
Linux Security
Linux Filesystems
Web Servers
Graphics & Desktop
PC Hardware
Windows
Problem Solutions
Privacy Policy

  




 

 

4.8.2 Using autoheader to Create config.h.in

The autoheader program can create a template file of C ‘#define’ statements for configure to use. If configure.ac invokes AC_CONFIG_HEADERS(file), autoheader creates file.in; if multiple file arguments are given, the first one is used. Otherwise, autoheader creates config.h.in.

In order to do its job, autoheader needs you to document all of the symbols that you might use. Typically this is done via an AC_DEFINE or AC_DEFINE_UNQUOTED call whose first argument is a literal symbol and whose third argument describes the symbol (see Defining Symbols). Alternatively, you can use AH_TEMPLATE (see Autoheader Macros), or you can supply a suitable input file for a subsequent configuration header file. Symbols defined by Autoconf's builtin tests are already documented properly; you need to document only those that you define yourself.

You might wonder why autoheader is needed: after all, why would configure need to “patch” a config.h.in to produce a config.h instead of just creating config.h from scratch? Well, when everything rocks, the answer is just that we are wasting our time maintaining autoheader: generating config.h directly is all that is needed. When things go wrong, however, you'll be thankful for the existence of autoheader.

The fact that the symbols are documented is important in order to check that config.h makes sense. The fact that there is a well-defined list of symbols that should be defined (or not) is also important for people who are porting packages to environments where configure cannot be run: they just have to fill in the blanks.

But let's come back to the point: the invocation of autoheader...

If you give autoheader an argument, it uses that file instead of configure.ac and writes the header file to the standard output instead of to config.h.in. If you give autoheader an argument of -, it reads the standard input instead of configure.ac and writes the header file to the standard output.

autoheader accepts the following options:

--help
-h
Print a summary of the command line options and exit.
--version
-V
Print the version number of Autoconf and exit.
--verbose
-v
Report processing steps.
--debug
-d
Don't remove the temporary files.
--force
-f
Remake the template file even if newer than its input files.
--include=dir
-I dir
Append dir to the include path. Multiple invocations accumulate.
--prepend-include=dir
-B dir
Prepend dir to the include path. Multiple invocations accumulate.
--warnings=category
-W category
Report the warnings related to category (which can actually be a comma separated list). Current categories include:
obsolete
report the uses of obsolete constructs
all
report all the warnings
none
report none
error
treats warnings as errors
no-category
disable warnings falling into category

 
 
  Published under the terms of the GNU General Public License Design by Interspire