1 \input texinfo @c -*-texinfo-*-
2 @comment $Id: gnulib.texi,v 1.27 2006-09-19 13:42:41 karl Exp $
3 @comment %**start of header
4 @setfilename gnulib.info
8 @comment %**end of header
10 @set UPDATED $Date: 2006-09-19 13:42:41 $
13 This manual is for GNU Gnulib (updated @value{UPDATED}),
14 which is a library of common routines intended to be shared at the
17 Copyright @copyright{} 2004, 2005, 2006 Free Software Foundation, Inc.
20 Permission is granted to copy, distribute and/or modify this document
21 under the terms of the GNU Free Documentation License, Version 1.1 or
22 any later version published by the Free Software Foundation; with no
23 Invariant Sections, with the Front-Cover Texts being ``A GNU Manual,''
24 and with the Back-Cover Texts as in (a) below. A copy of the
25 license is included in the section entitled ``GNU Free Documentation
28 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
29 this GNU Manual, like GNU software. Copies published by the Free
30 Software Foundation raise funds for GNU development.''
34 @dircategory Software development
36 * Gnulib: (gnulib). Source files to share among distributions.
41 @subtitle updated @value{UPDATED}
42 @author @email{bug-gnulib@@gnu.org}
44 @vskip 0pt plus 1filll
59 * Invoking gnulib-tool::
60 * Copying This Manual::
68 This manual contains some bare-bones documentation, but not much more.
69 It's mostly a place to store notes until someone (you?)@ gets around
70 to writing a coherent manual.
75 @item Gnulib is hosted at Savannah:
76 @url{http://savannah.gnu.org/projects/gnulib}. Get the sources
77 through CVS from there.
78 @item The Gnulib home page:
79 @url{http://www.gnu.org/software/gnulib/}.
89 * Out of memory handling::
90 * Library version handling::
91 * Regular expressions::
93 * Libtool and Windows::
94 * License Texinfo sources::
101 @cindex comments describing functions
102 @cindex describing functions, locating
103 Where to put comments describing functions: Because of risk of
104 divergence, we prefer to keep most function describing comments in
105 only one place: just above the actual function definition. Some
106 people prefer to put that documentation in the .h file. In any case,
107 it should appear in just one place unless you can ensure that the
108 multiple copies will always remain identical.
112 @section Header files
114 @cindex double inclusion of header files
115 @cindex header file include protection
116 It is a tradition to use CPP tricks to avoid parsing the same header
117 file more than once, which might cause warnings. The trick is to wrap
118 the content of the header file (say, @file{foo.h}) in a block, as in:
124 body of header file goes here
129 Whether to use @code{FOO_H} or @code{_FOO_H} is a matter of taste and
130 style. The C89 and C99 standards reserve all identifiers that begin with an
131 underscore and either an uppercase letter or another underscore, for
132 any use. Thus, in theory, an application might not safely assume that
133 @code{_FOO_H} has not already been defined by a library. On the other
134 hand, using @code{FOO_H} will likely lead the higher risk of
135 collisions with other symbols (e.g., @code{KEY_H}, @code{XK_H}, @code{BPF_H},
136 which are CPP macro constants, or @code{COFF_LONG_H}, which is a CPP
137 macro function). Your preference may depend on whether you consider
138 the header file under discussion as part of the application (which has
139 its own namespace for CPP symbols) or a supporting library (that
140 shouldn't interfere with the application's CPP symbol namespace).
142 @cindex C++ header files
143 @cindex Header files and C++
144 Adapting C header files for use in C++ applications can use another
153 body of header file goes here
160 The idea here is that @code{__cplusplus} is defined only by C++
161 implementations, which will wrap the header file in an @samp{extern "C"}
162 block. Again, whether to use this trick is a matter of taste and
163 style. While the above can be seen as harmless, it could be argued
164 that the header file is written in C, and any C++ application using it
165 should explicitly use the @samp{extern "C"} block itself. Your
166 preference might depend on whether you consider the API exported by
167 your header file as something available for C programs only, or for C
168 and C++ programs alike.
170 @subheading Include ordering
172 When writing a gnulib module, or even in general, a good way to order
173 the @samp{#include} directives is the following.
176 @item First comes the #include "..." specifying the module being implemented.
177 @item Then come all the #include <...> of system or system-replacement headers,
179 @item Then come all the #include "..." of gnulib and private headers, in
190 @include inet_ntoa.texi
193 @node Out of memory handling
194 @section Out of memory handling
196 @cindex Out of Memory handling
197 @cindex Memory allocation failure
198 The GSS API does not have a standard error code for the out of memory
199 error condition. Instead of adding a non-standard error code, this
200 library has chosen to adopt a different strategy. Out of memory
201 handling happens in rare situations, but performing the out of memory
202 error handling after almost all API function invocations pollute your
203 source code and might make it harder to spot more serious problems.
204 The strategy chosen improve code readability and robustness.
206 @cindex Aborting execution
207 For most applications, aborting the application with an error message
208 when the out of memory situation occur is the best that can be wished
209 for. This is how the library behaves by default.
211 @vindex xalloc_fail_func
212 However, we realize that some applications may not want to have the
213 GSS library abort execution in any situation. The GSS library support
214 a hook to let the application regain control and perform its own
215 cleanups when an out of memory situation has occurred. The application
216 can define a function (having a @code{void} prototype, i.e., no return
217 value and no parameters) and set the library variable
218 @code{xalloc_fail_func} to that function. The variable should be
222 extern void (*xalloc_fail_func) (void);
225 The GSS library will invoke this function if an out of memory error
226 occurs. Note that after this the GSS library is in an undefined
227 state, so you must unload or restart the application to continue call
228 GSS library functions. The hook is only intended to allow the
229 application to log the situation in a special way. Of course, care
230 must be taken to not allocate more memory, as that will likely also
234 @node Library version handling
235 @section Library version handling
237 The module @samp{check-version} can be useful when your gnulib
238 application is a system library. You will typically wrap the call to
239 the @code{check_version} function through a library API, your library
240 header file may contain:
243 #define STRINGPREP_VERSION "0.5.18"
245 extern const char *stringprep_check_version (const char *req_version);
248 To avoid ELF symbol collisions with other libraries that use the
249 @samp{check-version} module, add to @file{config.h} through a
250 AC_DEFINE something like:
253 AC_DEFINE(check_version, stringprep_check_version,
254 [Rename check_version.])
257 The @code{stringprep_check_version} function will thus be implemented
258 by the @code{check_version} module.
260 There are two uses of the interface. The first is a way to provide
261 for applications to find out the version number of the library it
262 uses. The application may contain diagnostic code such as:
265 printf ("Stringprep version: header %s library %s",
267 stringprep_check_version (NULL));
270 Separating the library and header file version can be useful when
271 searching for version mismatch related problems.
273 The second uses is as a rudimentary test of proper library version, by
274 making sure the application get a library version that is the same, or
275 newer, than the header file used when building the application. This
276 doesn't catch all problems, libraries may change backwards incompatibly
277 in later versions, but enable applications to require a certain
278 minimum version before it may proceed.
280 Typical uses look like:
283 /* Check version of libgcrypt. */
284 if (!gcry_check_version (GCRYPT_VERSION))
285 die ("version mismatch\n");
289 @node Regular expressions
290 @section Regular expressions
292 Gnulib supports many different types of regular expressions; although
293 the underlying features are the same or identical, the syntax used
294 varies. The descriptions given here for the different types are
295 generated automatically.
297 @include regexprops-generic.texi
300 @node Windows sockets
301 @section Windows sockets
303 There are several issues when building applications that should work
304 under Windows. The most problematic part is for applications that use
307 Hopefully, we can add helpful notes to this section that will help you
308 port your application to Windows using gnulib.
310 @subsection Getaddrinfo and WINVER
312 This was written for the getaddrinfo module, but may be applicable to
315 The getaddrinfo function exists in ws2tcpip.h and -lws2_32 on Windows
316 XP. The function declaration is present if @code{WINVER >= 0x0501}.
317 Windows 2000 does not have getaddrinfo in its @file{WS2_32.dll}.
319 Thus, if you want to assume Windows XP or later, you can add
320 AC_DEFINE(WINVER, 0x0501) to avoid compiling to (partial) getaddrinfo
323 If you want to support Windows 2000, don't do anything, but be aware
324 that gnulib will use its own (partial) getaddrinfo implementation even
325 on Windows XP. Currently the code does not attempt to determine if
326 the getaddrinfo function is available during runtime.
328 Todo: Make getaddrinfo.c open the WS2_32.DLL and check for the
329 getaddrinfo symbol and use it if present, otherwise fall back to our
332 @node Libtool and Windows
333 @section Libtool and Windows
335 If you want it to be possible to cross-compile your program to MinGW
336 and you use Libtool, you need to put:
342 in your @file{configure.ac}. This sets the correct names for the
343 @code{OBJDUMP}, @code{DLLTOOL}, and @code{AS} tools for the build.
345 If you are building a library, you will also need to pass
346 @code{-no-undefined} to make sure Libtool produces a DLL for your
347 library. From a @file{Makefile.am}:
350 libgsasl_la_LDFLAGS += -no-undefined
354 @node License Texinfo sources
355 @section License Texinfo sources
357 Gnulib provides copies of the GNU GPL, GNU LGPL, and GNU FDL licenses
358 in Texinfo form. (The master location is
359 @url{http://www.gnu.org/licenses/}). These Texinfo documents have
360 various node names and structures built into them; for your manual,
361 you might like to change these. It's ok to do this, and a convenient
362 way to do so is to use a context diff and the @option{--local-dir}
363 option to @command{gnulib-tool}.
365 Of course the license texts themselves should not be changed at all.
368 @include gnulib-tool.texi
371 @node Copying This Manual
372 @appendix Copying This Manual
375 * GNU Free Documentation License:: License for copying this manual.