X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;f=doc%2Fgnulib.texi;h=59a9338ba64e740efe16c8afd222e6c93d870eb1;hb=19931efa2e7efbc7dbdc282178d73f4d97cabb3e;hp=72ef89903e553147fed71d3f9c036cf9e42fee4e;hpb=cd5276f642f0c8e1bbdb59526412fd99ad583827;p=gnulib.git diff --git a/doc/gnulib.texi b/doc/gnulib.texi index 72ef89903..59a9338ba 100644 --- a/doc/gnulib.texi +++ b/doc/gnulib.texi @@ -1,5 +1,5 @@ \input texinfo @c -*-texinfo-*- -@comment $Id: gnulib.texi,v 1.2 2004-09-23 23:13:19 karl Exp $ +@comment $Id: gnulib.texi,v 1.9 2005-05-23 11:05:53 jas Exp $ @comment %**start of header @setfilename gnulib.info @settitle GNU Gnulib @@ -7,14 +7,14 @@ @syncodeindex pg cp @comment %**end of header -@set UPDATED $Date: 2004-09-23 23:13:19 $ +@set UPDATED $Date: 2005-05-23 11:05:53 $ @copying This manual is for GNU Gnulib (updated @value{UPDATED}), which is a library of common routines intended to be shared at the source level. -Copyright @copyright{} 2004 Free Software Foundation, Inc. +Copyright @copyright{} 2004, 2005 Free Software Foundation, Inc. @quotation Permission is granted to copy, distribute and/or modify this document @@ -33,7 +33,7 @@ Software Foundation raise funds for GNU development.'' @dircategory Software development @direntry -* gnulib: (gnulib). Source files to share among distributions. +* Gnulib: (gnulib). Source files to share among distributions. @end direntry @titlepage @@ -65,8 +65,9 @@ Software Foundation raise funds for GNU development.'' @node Gnulib @chapter Gnulib -This is not a real manual. It's just a place to store random notes -until someone (you?) gets around to actually writing a manual. +This manual contains some bare-bones documentation, but not much more. +It's mostly been a place to store notes until someone (you?) gets +around to writing a coherent manual. Getting started: @@ -80,6 +81,7 @@ Getting started: @menu * Comments:: +* Header files:: * ctime:: * inet_ntoa:: * Out of memory handling:: @@ -98,6 +100,78 @@ it should appear in just one place unless you can ensure that the multiple copies will always remain identical. +@node Header files +@section Header files + +@cindex double inclusion of header files +@cindex header file include protection +It is a tradition to use CPP tricks to avoid parsing the same header +file more than once, which might cause warnings. The trick is to wrap +the content of the header file (say, @file{foo.h}) in a block, as in: + +@example +#ifndef FOO_H +# define FOO_H +... +body of header file goes here +... +#endif /* FOO_H */ +@end example + +Whether to use @code{FOO_H} or @code{_FOO_H} is a matter of taste and +style. The C89 and C99 standards reserve all identifiers that begin with an +underscore and either an uppercase letter or another underscore, for +any use. Thus, in theory, an application might not safely assume that +@code{_FOO_H} has not already been defined by a library. On the other +hand, using @code{FOO_H} will likely lead the higher risk of +collisions with other symbols (e.g., @code{KEY_H}, @code{XK_H}, @code{BPF_H}, +which are CPP macro constants, or @code{COFF_LONG_H}, which is a CPP +macro function). Your preference may depend on whether you consider +the header file under discussion as part of the application (which has +its own namespace for CPP symbols) or a supporting library (that +shouldn't interfere with the application's CPP symbol namespace). + +@cindex C++ header files +@cindex Header files and C++ +Adapting C header files for use in C++ applications can use another +CPP trick, as in: + +@example +# ifdef __cplusplus +extern "C" +@{ +# endif +... +body of header file goes here +... +# ifdef __cplusplus +@} +# endif +@end example + +The idea here is that @code{__cplusplus} is defined only by C++ +implementations, which will wrap the header file in an @samp{extern "C"} +block. Again, whether to use this trick is a matter of taste and +style. While the above can be seen as harmless, it could be argued +that the header file is written in C, and any C++ application using it +should explicitly use the @samp{extern "C"} block itself. Your +preference might depend on whether you consider the API exported by +your header file as something available for C programs only, or for C +and C++ programs alike. + +@subsection Include ordering + +When writing a gnulib module, or even in general, a good way to order +the @samp{#include} directives is the following. + +@itemize +@item First comes the #include "..." specifying the module being implemented. +@item Then come all the #include <...> of system or system-replacement headers, +in arbitrary order. +@item Then come all the #include "..." of gnulib and private headers, in +arbitrary order. +@end itemize + @node ctime @section ctime @findex ctime @@ -219,6 +293,9 @@ Creating ./lib/Makefile.am... Creating ./m4/gnulib.m4... Finished. +You may need to add #include directives for the following .h files. + #include "strdup.h" + Don't forget to add "lib/Makefile" to AC_CONFIG_FILES in "./configure.ac" and to mention "lib" in SUBDIRS in some Makefile.am. @@ -230,6 +307,15 @@ macros in @file{m4/}. You can override these paths by using @code{--source-base=DIRECTORY} and @code{--m4-base=DIRECTORY}, or by adding @samp{gl_SOURCE_BASE(DIRECTORY)} and @samp{gl_M4_BASE(DIRECTORY)} to your @file{configure.ac}. +Some modules also provide other files necessary +for building. These files are copied into the directory specified +by @samp{AC_CONFIG_AUX_DIR} in @file{configure.ac} or by the +@code{--aux-dir=DIRECTORY} option. If neither is specified, the +current directory is assumed. + +@code{gnulib-tool} can make symbolic links instead +of copying the source files. Use the @code{--symbolic} +(or @code{-s} for short) option to do this. @code{gnulib-tool} will overwrite any pre-existing files, in particular @file{Makefile.am}. Unfortunately, separating the @@ -323,14 +409,15 @@ If you are using a gnulib source base of @code{gl}, you would use: SUBDIRS += gl @end example -Finally, you have add C flags and LD flags, so that you can make use +Finally, you have to add compiler and linker flags in the appropriate +source directories, so that you can make use of the gnulib library. For example: @example ... AM_CPPFLAGS = -I$(top_srcdir)/lib ... -LIBADD = lib/libgnu.la +LIBADD = lib/libgnu.a ... @end example