\input texinfo          @c -*-texinfo-*-
@comment %**start of header
@setfilename libunistring.info
@documentencoding UTF-8
@settitle GNU libunistring
@finalout
@c Indices:
@c   am = autoconf macro  @amindex
@c   cp = concept         @cindex
@c   fn = function        @findex
@c   tp = type            @tindex
@c Unused predefined indices:
@c   ky = keystroke       @kindex
@c   pg = program         @pindex
@c   vr = variable        @vindex
@defcodeindex am
@syncodeindex am cp
@syncodeindex fn cp
@syncodeindex tp cp
@ifclear texi2html
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@c texi2html-1.76 does not support @arrow{}.
@ifset texi2html
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@include version.texi

@c Location of the POSIX specification on the web.
@set POSIXURL http://pubs.opengroup.org/onlinepubs/9699919799

@c Macro for referencing a POSIX header.
@ifinfo
@macro posixheader{header}
@code{<\header\>}
@end macro
@end ifinfo
@ifnotinfo
@macro posixheader{header}
@uref{@value{POSIXURL}/basedefs/\header\.html,,@code{<\header\>}}
@end macro
@end ifnotinfo

@c Macro for referencing a POSIX function.
@c We don't write it as func(), see section "GNU Manuals" of the
@c GNU coding standards.
@ifinfo
@macro posixfunc{func}
@code{\func\}
@end macro
@end ifinfo
@ifnotinfo
@macro posixfunc{func}
@uref{@value{POSIXURL}/functions/\func\.html,,@code{\func\}}
@end macro
@end ifnotinfo

@c Macro for referencing a normal function.
@c We don't write it as func(), see section "GNU Manuals" of the
@c GNU coding standards.
@macro func{func}
@code{\func\}
@end macro

@c Macro for an advisory ragged line break in TeX mode.
@c Needed because there are long unbreakable pieces of text (such as URLs or
@c formulas), TeX is too shy to move them to a new line. TeX considers only
@c two choices: a line break in aligned mode (which it rejects due to aesthetic
@c reasons) and writing into the margin. What we want in many cases is a line
@c break without filling the first line. Like what @* delivers. But we want it
@c only when needed, so that it disappears when unrelated changes in the same
@c paragraph cause a line break in a nearby position. And we need it only in
@c TeX mode. info and HTML modes are fine.
@c This trick is from Karl Berry.
@iftex
@macro texnl
@hfil@penalty9000@hfilneg
@end macro
@end iftex
@ifnottex
@macro texnl
@end macro
@end ifnottex

@ifinfo
@dircategory Software development
@direntry
* GNU libunistring: (libunistring).     Unicode string library.
@end direntry
@end ifinfo

@ifinfo
This manual is for GNU libunistring.

@ignore
@c This was: @copying but it triggers a makeinfo 4.13 bug
Copyright (C) 2001-2024 Free Software Foundation, Inc.

This manual is free documentation.  It is dually licensed under the
GNU FDL and the GNU GPL.  This means that you can redistribute this
manual under either of these two licenses, at your choice.

This manual is covered by the GNU FDL.  Permission is granted to copy,
distribute and/or modify this document under the terms of the
GNU Free Documentation License (FDL), either version 1.2 of the
License, or (at your option) any later version published by the
Free Software Foundation (FSF); with no Invariant Sections, with no
Front-Cover Text, and with no Back-Cover Texts.
A copy of the license is included in @ref{GNU FDL}.

This manual is covered by the GNU GPL.  You can redistribute it and/or
modify it under the terms of the GNU General Public License (GPL), either
version 3 of the License, or (at your option) any later version published
by the Free Software Foundation (FSF).
A copy of the license is included in @ref{GNU GPL}.
@end ignore
@end ifinfo

@titlepage
@title GNU libunistring, version @value{VERSION}
@subtitle updated @value{UPDATED}
@author Bruno Haible

@ifnothtml
@page
@vskip 0pt plus 1filll
@c @insertcopying
Copyright (C) 2001-2024 Free Software Foundation, Inc.

This manual is free documentation.  It is dually licensed under the
GNU FDL and the GNU GPL.  This means that you can redistribute this
manual under either of these two licenses, at your choice.

This manual is covered by the GNU FDL.  Permission is granted to copy,
distribute and/or modify this document under the terms of the
GNU Free Documentation License (FDL), either version 1.2 of the
License, or (at your option) any later version published by the
Free Software Foundation (FSF); with no Invariant Sections, with no
Front-Cover Text, and with no Back-Cover Texts.
A copy of the license is included in @ref{GNU FDL}.

This manual is covered by the GNU GPL.  You can redistribute it and/or
modify it under the terms of the GNU General Public License (GPL), either
version 3 of the License, or (at your option) any later version published
by the Free Software Foundation (FSF).
A copy of the license is included in @ref{GNU GPL}.
@end ifnothtml
@end titlepage

@c Table of Contents
@contents

@ifnottex
@node Top
@top GNU libunistring
@end ifnottex

@menu
* Introduction::                Who may need Unicode strings?
* Conventions::                 Conventions used in this manual
* unitypes.h::                  Elementary types
* unistr.h::                    Elementary Unicode string functions
* uniconv.h::                   Conversions between Unicode and encodings
* unistdio.h::                  Output with Unicode strings
* uniname.h::                   Names of Unicode characters
* unictype.h::                  Unicode character classification and properties
* uniwidth.h::                  Display width
* unigbrk.h::                   Grapheme cluster breaking
* uniwbrk.h::                   Word breaks in strings
* unilbrk.h::                   Line breaking
* uninorm.h::                   Normalization forms
* unicase.h::                   Case mappings
* uniregex.h::                  Regular expressions
* Using the library::           How to link with the library and use it?
* More functionality::          More advanced functionality
* The wchar_t mess::            Why @code{wchar_t *} strings are useless
* The char32_t problem::        Why @code{char32_t *} strings are problematic
* Licenses::                    Licenses

* Index::                       General Index

@detailmenu
 --- The Detailed Node Listing ---

Introduction

* Unicode::                     What is Unicode?
* Unicode and i18n::            Unicode and internationalization
* Locale encodings::            What is a locale encoding?
* In-memory representation::    How to represent strings in memory?
* char * strings::              What to keep in mind with @code{char *} strings
* Unicode strings::             How are Unicode strings represented?

unistr.h

* Elementary string checks::
* Elementary string conversions::
* Elementary string functions::
* Elementary string functions with memory allocation::
* Elementary string functions on NUL terminated strings::

Elementary string functions

* Iterating::
* Creating Unicode strings::
* Copying Unicode strings::
* Comparing Unicode strings::
* Searching for a character::
* Counting characters::

Elementary string functions on NUL terminated strings

* Iterating over a NUL terminated Unicode string::
* Length::
* Copying a NUL terminated Unicode string::
* Comparing NUL terminated Unicode strings::
* Duplicating a NUL terminated Unicode string::
* Searching for a character in a NUL terminated Unicode string::
* Searching for a substring::
* Tokenizing::

unictype.h

* General category::
* Canonical combining class::
* Bidi class::
* Decimal digit value::
* Digit value::
* Numeric value::
* Mirrored character::
* Arabic shaping::
* Properties::
* Scripts::
* Blocks::
* ISO C and Java syntax::
* Classifications like in ISO C::

General category

* Object oriented API::
* Bit mask API::

Properties

* Properties as objects::
* Properties as functions::

unigbrk.h

* Grapheme cluster breaks in a string::
* Grapheme cluster break property::

uniwbrk.h

* Word breaks in a string::
* Word break property::

uninorm.h

* Decomposition of characters::
* Composition of characters::
* Normalization of strings::
* Normalizing comparisons::
* Normalization of streams::

unicase,h

* Case mappings of characters::
* Case mappings of strings::
* Case mappings of substrings::
* Case insensitive comparison::
* Case detection::

Using the library

* Installation::
* Compiler options::
* Include files::
* Autoconf macro::
* Reporting problems::

Licenses

* GNU GPL::                     GNU General Public License
* GNU LGPL::                    GNU Lesser General Public License
* GNU FDL::                     GNU Free Documentation License

@end detailmenu
@end menu

@node Introduction
@chapter Introduction

This library provides functions for manipulating Unicode strings and
for manipulating C strings according to the Unicode standard.

It consists of the following parts:

@table @code
@item <unistr.h>
elementary string functions
@item <uniconv.h>
conversion from/to legacy encodings
@item <unistdio.h>
formatted output to strings
@item <uniname.h>
character names
@item <unictype.h>
character classification and properties
@item <uniwidth.h>
string width when using nonproportional fonts
@item <unigbrk.h>
grapheme cluster breaks
@item <uniwbrk.h>
word breaks
@item <unilbrk.h>
line breaking algorithm
@item <uninorm.h>
normalization (composition and decomposition)
@item <unicase.h>
case folding
@item <uniregex.h>
regular expressions (not yet implemented)
@end table

@cindex use cases
@cindex value, of libunistring
libunistring is for you if your application involves non-trivial text
processing, such as upper/lower case conversions, line breaking, operations
on words, or more advanced analysis of text.  Text provided by the user can,
in general, contain characters of all kinds of scripts.  The text processing
functions provided by this library handle all scripts and all languages.

libunistring is for you if your application already uses the ISO C / POSIX
@posixheader{ctype.h}, @posixheader{wctype.h} functions and the text it
operates on is provided by the user and can be in any language.

libunistring is also for you if your application uses Unicode strings as
internal in-memory representation.

@menu
* Unicode::                     What is Unicode?
* Unicode and i18n::            Unicode and internationalization
* Locale encodings::            What is a locale encoding?
* In-memory representation::    How to represent strings in memory?
* char * strings::              What to keep in mind with @code{char *} strings
* Unicode strings::             How are Unicode strings represented?
@end menu

@node Unicode
@section Unicode

@cindex Unicode
Unicode is a standardized repertoire of characters that contains characters
from all scripts of the world, from Latin letters to Chinese ideographs
and Babylonian cuneiform glyphs.  It also specifies how these characters
are to be rendered on a screen or on paper, and how common text processing
(word selection, line breaking, uppercasing of page titles etc.) is supposed
to behave on Unicode text.

Unicode also specifies three ways of storing sequences of Unicode
characters in a computer whose basic unit of data is an 8-bit byte:
@cindex UTF-8
@cindex UTF-16
@cindex UTF-32
@cindex UCS-4
@table @asis
@item UTF-8
Every character is represented as 1 to 4 bytes.
@item UTF-16
Every character is represented as 1 to 2 units of 16 bits.
@item UTF-32, a.k.a@. UCS-4
Every character is represented as 1 unit of 32 bits.
@end table

For encoding Unicode text in a file, UTF-8 is usually used.  For encoding
Unicode strings in memory for a program, either of the three encoding forms
can be reasonably used.

Unicode is widely used on the web.  Prior to the use of Unicode, web pages
were in many different encodings (ISO-8859-1 for English, French, Spanish,
ISO-8859-2 for Polish, ISO-8859-7 for Greek, KOI8-R for Russian, GB2312 or
BIG5 for Chinese, ISO-2022-JP-2 or EUC-JP or Shift_JIS for Japanese, and many
many others).  It was next to impossible to create a document that contained
Chinese and Polish text in the same document.  Due to the many encodings for
Japanese, even the processing of pure Japanese text was error prone.

References:
@itemize @bullet
@item
The Unicode standard:@texnl{} @url{https://www.unicode.org/}
@item
Definition of UTF-8:@texnl{} @url{https://www.rfc-editor.org/rfc/rfc3629.txt}
@item
Definition of UTF-16:@texnl{} @url{https://www.rfc-editor.org/rfc/rfc2781.txt}
@item
Markus Kuhn's UTF-8 and Unicode FAQ:@texnl{}
@url{https://www.cl.cam.ac.uk/~mgk25/unicode.html}
@end itemize

@node Unicode and i18n
@section Unicode and Internationalization

@cindex internationalization
Internationalization is the process of changing the source code of a program
so that it can meet the expectations of users in any culture, if culture
specific data (translations, images etc.) are provided.

Use of Unicode is not strictly required for internationalization, but it
makes internationalization much easier, because operations that need to
look at specific characters (like hyphenation, spell checking, or the
automatic conversion of double-quotes to opening and closing double-quote
characters) don't need to consider multiple possible encodings of the text.

Use of Unicode also enables multilingualization: the ability of having text
in multiple languages present in the same document or even in the same line
of text.

But use of Unicode is not everything.  Internationalization usually consists
of four features:
@itemize @bullet
@item
Use of Unicode where needed for text processing.  This is what this library
is for.
@item
Use of message catalogs for messages shown to the user, This is what
GNU gettext is about.
@item
Use of locale specific conventions for date and time formats, for numeric
formatting, or for sorting of text.  This can be done adequately with the
POSIX APIs and the implementation of locales in the GNU C library.
@item
In graphical user interfaces, adapting the GUI to the default text direction
of the current locale (see
@url{https://en.wikipedia.org/wiki/Right-to-left,right-to-left languages}).
@end itemize

@node Locale encodings
@section Locale encodings

@cindex locale
A locale is a set of cultural conventions.  According to POSIX, for a program,
at any moment, there is one locale being designated as the ``current locale''.
(Actually, POSIX supports also one locale per thread, but this feature is not
yet universally implemented and not widely used.)
@cindex locale categories
The locale is partitioned into several aspects, called the ``categories''
of the locale.  The main various aspects are:
@itemize @bullet
@item
The character encoding and the character properties.  This is the
@code{LC_CTYPE} category.
@item
The sorting rules for text.  This is the @code{LC_COLLATE} category.
@item
The language specific translations of messages.  This is the
@code{LC_MESSAGES} category.
@item
The formatting rules for numbers, such as the decimal separator.  This is
the @code{LC_NUMERIC} category.
@item
The formatting rules for amounts of money.  This is the @code{LC_MONETARY}
category.
@item
The formatting of date and time.  This is the @code{LC_TIME} category.
@end itemize

@cindex locale encoding
In particular, the @code{LC_CTYPE} category of the current locale determines
the character encoding.  This is the encoding of @samp{char *} strings.
We also call it the ``locale encoding''.  GNU libunistring has a function,
@func{locale_charset}, that returns a standardized (platform independent)
name for this encoding.

All locale encodings used on glibc systems are essentially ASCII compatible:
Most graphic ASCII characters have the same representation, as a single byte,
in that encoding as in ASCII.

Among the possible locale encodings are UTF-8 and GB18030.  Both allow
to represent any Unicode character as a sequence of bytes.  UTF-8 is used in
most of the world, whereas GB18030 is used in the People's Republic of China,
because it is backward compatible with the GB2312 encoding that was used in
this country earlier.

The legacy locale encodings, ISO-8859-15 (which supplanted ISO-8859-1 in
most of Europe), ISO-8859-2, KOI8-R, EUC-JP, etc., are still in use in
some places, though.

UTF-16 and UTF-32 are not used as locale encodings, because they are not
ASCII compatible.

@node In-memory representation
@section Choice of in-memory representation of strings

There are three ways of representing strings in memory of a running
program.
@itemize @bullet
@item
As @samp{char *} strings.  Such strings are represented in locale encoding.
This approach is employed when not much text processing is done by the
program.  When some Unicode aware processing is to be done, a string is
converted to Unicode on the fly and back to locale encoding afterwards.
@item
As UTF-8 or UTF-16 or UTF-32 strings.  This implies that conversion from
locale encoding to Unicode is performed on input, and in the opposite
direction on output.  This approach is employed when the program does
a significant amount of text processing, or when the program has multiple
threads operating on the same data but in different locales.
@item
As @samp{wchar_t *}, a.k.a@. ``wide strings''.  This approach is misguided,
see @ref{The wchar_t mess}.
@end itemize

Of course, a @samp{char *} string can, in some cases, be encoded in UTF-8.
You will use the data type depending on what you can guarantee about how
it's encoded: If a string is encoded in the locale encoding, or if you
don't know how it's encoded, use @samp{char *}.  If, on the other hand,
you can @emph{guarantee} that it is UTF-8 encoded, then you can use the
UTF-8 string type, @code{uint8_t *}, for it.

The five types @code{char *}, @code{uint8_t *}, @code{uint16_t *},
@code{uint32_t *}, and @code{wchar_t *} are incompatible types at the C
level.  Therefore, @samp{gcc -Wall} will produce a warning if, by mistake,
your code contains a mismatch between these types.  In the context of
using GNU libunistring, even a warning about a mismatch between
@code{char *} and @code{uint8_t *} is a sign of a bug in your code
that you should not try to silence through a cast.

@node char * strings
@section @samp{char *} strings

@cindex C string functions
The classical C strings, with its C library support standardized by
ISO C and POSIX, can be used in internationalized programs with some
precautions.  The problem with this API is that many of the C library
functions for strings don't work correctly on strings in locale
encodings, leading to bugs that only people in some cultures of the
world will experience.

@cindex locale, multibyte
The first problem with the C library API is the support of multibyte
locales.  According to the locale encoding, in general, every character
is represented by one or more bytes (up to 4 bytes in practice --- but
use @code{MB_LEN_MAX} instead of the number 4 in the code).
When every character is represented by only 1 byte, we speak of an
``unibyte locale'', otherwise of a ``multibyte locale''.  It is important
to realize that the majority of Unix installations nowadays use UTF-8
or GB18030 as locale encoding; therefore, the majority of users are
using multibyte locales.

@cindex char, type
The important fact to remember is:
@cartouche
@emph{A @samp{char} is a byte, not a character.}
@end cartouche

As a consequence:
@itemize @bullet
@item
The @posixheader{ctype.h} API is useless in this context; it does not work in
multibyte locales.
@item
The @posixfunc{strlen} function does not return the number of characters
in a string.  Nor does it return the number of screen columns occupied
by a string after it is output.  It merely returns the number of
@emph{bytes} occupied by a string.
@item
Truncating a string, for example, with @posixfunc{strncpy}, can have the
effect of truncating it in the middle of a multibyte character.  Such
a string will, when output, have a garbled character at its end, often
represented by a hollow box.
@item
@posixfunc{strchr} and @posixfunc{strrchr} do not work with multibyte strings
if the locale encoding is GB18030 and the character to be searched is
a digit.
@item
@posixfunc{strstr} does not work with multibyte strings if the locale encoding
is different from UTF-8.
@item
@posixfunc{strcspn}, @posixfunc{strpbrk}, @posixfunc{strspn} cannot work
correctly in multibyte locales: they assume the second argument is a list of
single-byte characters.  Even in this simple case, they do not work with
multibyte strings if the locale encoding is GB18030 and one of the
characters to be searched is a digit.
@item
@posixfunc{strsep} and @posixfunc{strtok_r} do not work with multibyte strings
unless all of the delimiter characters are ASCII characters < 0x30.
@item
The @posixfunc{strcasecmp}, @posixfunc{strncasecmp}, and @posixfunc{strcasestr}
functions do not work with multibyte strings.
@end itemize

The workarounds can be found in GNU gnulib
@url{https://www.gnu.org/software/gnulib/}.
@itemize @bullet
@item
gnulib has modules @samp{mbchar}, @samp{mbiter}, @samp{mbuiter} that
represent multibyte characters and allow to iterate across a multibyte
string with the same ease as through a unibyte string.
@item
gnulib has functions @func{mbslen} and @func{mbswidth} that can be
used instead of @posixfunc{strlen} when the number of characters or the
number of screen columns of a string is requested.
@item
gnulib has functions @func{mbschr} and @func{mbsrrchr} that are
like @posixfunc{strchr} and @posixfunc{strrchr}, but work in multibyte locales.
@item
gnulib has a function @func{mbsstr} that is like @posixfunc{strstr}, but works
in multibyte locales.
@item
gnulib has functions @func{mbscspn}, @func{mbspbrk}, @func{mbsspn}
that are like @posixfunc{strcspn}, @posixfunc{strpbrk}, @posixfunc{strspn}, but
work in multibyte locales.
@item
gnulib has functions @func{mbssep} and @func{mbstok_r} that are
like @posixfunc{strsep} and @posixfunc{strtok_r} but work in multibyte locales.
@item
gnulib has functions @func{mbscasecmp}, @func{mbsncasecmp},
@func{mbspcasecmp}, and @func{mbscasestr} that are like @posixfunc{strcasecmp},
@posixfunc{strncasecmp}, and @posixfunc{strcasestr}, but
work in multibyte locales.  Still, the function @code{ulc_casecmp} is
preferable to these functions; see below.
@end itemize

The second problem with the C library API is that it has some assumptions built-in that are not valid in some languages:
@itemize @bullet
@item
It assumes that there are only two forms of every character: uppercase
and lowercase.  This is not true for Croatian, where the character
@sc{LETTER DZ WITH CARON} comes in three forms:
@sc{LATIN CAPITAL LETTER DZ WITH CARON} (DZ),
@sc{LATIN CAPITAL LETTER D WITH SMALL LETTER Z WITH CARON} (Dz),
@sc{LATIN SMALL LETTER DZ WITH CARON} (dz).
@item
It assumes that uppercasing of 1 character leads to 1 character.  This
is not true for German, where the @sc{LATIN SMALL LETTER SHARP S}, when
uppercased, becomes @samp{SS}.
@item
It assumes that there is 1:1 mapping between uppercase and lowercase forms.
This is not true for the Greek sigma: @sc{GREEK CAPITAL LETTER SIGMA} is
the uppercase of both @sc{GREEK SMALL LETTER SIGMA} and
@sc{GREEK SMALL LETTER FINAL SIGMA}.
@item
It assumes that the upper/lowercase mappings are position independent.
This is not true for the Greek sigma and the Lithuanian i.
@end itemize

The correct way to deal with this problem is
@enumerate
@item
to provide functions for titlecasing, as well as for upper- and
lowercasing,
@item
to view case transformations as functions that operates on strings,
rather than on characters.
@end enumerate

This is implemented in this library, through the functions declared in @code{<unicase.h>}, see @ref{unicase.h}.

@node Unicode strings
@section Unicode strings

libunistring supports Unicode strings in three representations:
@cindex UTF-8, strings
@cindex UTF-16, strings
@cindex UTF-32, strings
@itemize @bullet
@item
UTF-8 strings, through the type @samp{uint8_t *}.  The units are bytes
(@code{uint8_t}).
@item
UTF-16 strings, through the type @samp{uint16_t *},  The units are 16-bit
memory words (@code{uint16_t}).
@item
UTF-32 strings, through the type @samp{uint32_t *}.  The units are 32-bit
memory words (@code{uint32_t}).
@end itemize

As with C strings, there are two variants:
@itemize @bullet
@item
Unicode strings with a terminating NUL character are represented as
a pointer to the first unit of the string.  There is a unit containing
a 0 value at the end.  It is considered part of the string for all
memory allocation purposes, but is not considered part of the string
for all other logical purposes.
@item
Unicode strings where embedded NUL characters are allowed.  These
are represented by a pointer to the first unit and the number of units
(not bytes!) of the string.  In this setting, there is no trailing
zero-valued unit used as ``end marker''.
@end itemize

@node Conventions
@chapter Conventions

This chapter explains conventions valid throughout the libunistring library.

@cindex argument conventions
Variables of type @code{char *} denote C strings in locale encoding.
See @ref{Locale encodings}.

Variables of type @code{uint8_t *} denote UTF-8 strings.  Their units
are bytes.

Variables of type @code{uint16_t *} denote UTF-16 strings, without byte
order mark.  Their units are 2-byte words.

Variables of type @code{uint32_t *} denote UTF-32 strings, without byte
order mark.  Their units are 4-byte words.

Argument pairs @code{(@var{s}, @var{n})} denote a string
@code{@var{s}[0..@var{n}-1]} with exactly @var{n} units.@footnote{A NUL
unit as terminator is not needed, since the number of units is given by
@var{n}.  If some of the units of the string are NUL, they are just
regular units; they are not interpreted as terminators.}

All functions with prefix @samp{ulc_} operate on C strings in locale
encoding.

All functions with prefix @samp{u8_} operate on UTF-8 strings.

All functions with prefix @samp{u16_} operate on UTF-16 strings.

All functions with prefix @samp{u32_} operate on UTF-32 strings.

For every function with prefix @samp{u8_}, operating on UTF-8 strings,
there is also a corresponding function with prefix @samp{u16_},
operating on UTF-16 strings, and a corresponding function with prefix
@samp{u32_}, operating on UTF-32 strings.  Their description is
analogous; in this documentation we describe only the function that
operates on UTF-8 strings, for brevity.

A declaration with a variable @var{n} denotes the three concrete
declarations with @var{n} = 8, @var{n} = 16, @var{n} = 32.

All parameters starting with @samp{str} and the parameters of
functions starting with @code{u8_str}/@code{u16_str}/@code{u32_str}
denote a NUL terminated string.

@cindex return value conventions
Error values are always returned through the @code{errno} variable,
usually with a return value that indicates the presence of an error
(NULL for functions that return an pointer, or -1 for functions that
return an @code{int}).

Functions returning a string result take a
@code{(@var{resultbuf}, @var{lengthp})}
argument pair.  If @var{resultbuf} is not NULL and the result fits
into @code{*@var{lengthp}} units, it is put in @var{resultbuf}, and
@var{resultbuf} is returned.  Otherwise, a freshly allocated string
is returned.  In both cases, @code{*@var{lengthp}} is set to the
length (number of units) of the returned string.  In case of error,
NULL is returned and @code{errno} is set.

To invoke such a function:
@itemize @bullet
@item
First ask yourself whether you want to accept the overhead of a
@code{malloc} invocation even for a small-sized result.
If yes, pass NULL as @var{resultbuf}.
If no, allocate an array of units on the stack, typically between 50 and
4000 bytes large; pass this array as @var{resultbuf}; and initialize
@code{*@var{lengthp}} to the number of units of this array.
@item
Upon return from such a function, look at the return value:
NULL means an error; look at the value of @code{errno} in this case.
Otherwise, the return value is the result, with @code{*@var{lengthp}}
units.  Note that the function has @emph{not} added an extra NUL
character at the end.
@item
Finally, do memory management.  You know that the result was
@code{malloc}-allocated if it is @code{!= NULL} and
@code{!= @var{resultbuf}}.
@end itemize

@include unitypes.texi
@include unistr.texi
@include uniconv.texi
@include unistdio.texi
@include uniname.texi
@include unictype.texi
@include uniwidth.texi
@include unigbrk.texi
@include uniwbrk.texi
@include unilbrk.texi
@include uninorm.texi
@include unicase.texi
@include uniregex.texi

@node Using the library
@chapter Using the library

This chapter explains some practical considerations, regarding the
installation and compiler options that are needed in order to use this
library.

@menu
* Installation::
* Compiler options::
* Include files::
* Autoconf macro::
* Reporting problems::
@end menu

@node Installation
@section Installation

@cindex dependencies
Before you can use the library, it must be installed.  First, you have to
make sure all dependencies are installed.  They are listed in the file
@file{DEPENDENCIES}.

@cindex installation
Then you can proceed to build and install the library, as described in the
file @file{INSTALL}.  For installation on Windows systems, please refer to
the file @file{INSTALL.windows}.

@node Compiler options
@section Compiler options

Let's denote as @code{LIBUNISTRING_PREFIX} the value of the @samp{--prefix}
option that you passed to @code{configure} while installing this package.
If you didn't pass any @samp{--prefix} option, then the package is installed
in @file{/usr/local}.

Let's denote as @code{LIBUNISTRING_INCLUDEDIR} the directory where the
include files were installed.  This is usually the same as
@code{$@{LIBUNISTRING_PREFIX@}/include}.  Except that if you passed an
@samp{--includedir} option to @code{configure}, it is the value of that
option.

Let's further denote as @code{LIBUNISTRING_LIBDIR} the directory where
the library itself was installed.  This is the value that you passed
with the @samp{--libdir} option to @code{configure}, or otherwise the
same as @code{$@{LIBUNISTRING_PREFIX@}/lib}.  Recall that when building
in 64-bit mode on a 64-bit GNU/Linux system that supports executables
in either 64-bit mode or 32-bit mode, you should have used the option
@code{--libdir=$@{LIBUNISTRING_PREFIX@}/lib64}.

@cindex compiler options
So that the compiler finds the include files, you have to pass it the
option @code{-I$@{LIBUNISTRING_INCLUDEDIR@}}.

So that the compiler finds the library during its linking pass, you have
to pass it the options @code{-L$@{LIBUNISTRING_LIBDIR@} -lunistring}.
On some systems, in some configurations, you also have to pass options
needed for linking with @code{libiconv}.  The autoconf macro
@code{gl_LIBUNISTRING} (see @ref{Autoconf macro}) deals with this
particularity.

@node Include files
@section Include files

Most of the include files have been presented in the introduction, see
@ref{Introduction}, and subsequent detailed chapters.

Another include file is @code{<unistring/version.h>}. It contains the
version number of the libunistring library.

@deftypevr Macro int _LIBUNISTRING_VERSION
This constant contains the version of libunistring that is being used
at compile time.
It encodes the major, minor, and subminor parts of the version number.
These parts are encoded in the form @code{(major<<16) + (minor<<8) + subminor}.
@end deftypevr

@deftypevr Constant int _libunistring_version
This constant contains the version of libunistring that is being used
at run time.
It encodes the major, minor, and subminor parts of the version number.
These parts are encoded in the form @code{(major<<16) + (minor<<8) + subminor}.
@end deftypevr

It is possible that @code{_libunistring_version} is greater than
@code{_LIBUNISTRING_VERSION}.  This can happen when you use
@code{libunistring} as a shared library, and a newer, binary
backward-compatible version has been installed after your program
that uses @code{libunistring} was installed.

@code{<unistring/version.h>} also contains:

@deftypevr Constant int _libunistring_unicode_version
This constant contains the version of the Unicode standard that is
implemented by libunistring.
It encodes the major and minor parts of the version number only.
These parts are encoded in the form @code{(major<<8) + minor}.
@end deftypevr

@node Autoconf macro
@section Autoconf macro

@cindex autoconf macro
GNU Gnulib provides an autoconf macro that tests for the availability
of @code{libunistring}.  It is contained in the Gnulib module
@samp{libunistring}, see@texnl{}
@url{https://www.gnu.org/software/gnulib/MODULES.html#module=libunistring}.

@amindex gl_LIBUNISTRING
The macro is called @code{gl_LIBUNISTRING}.  It searches for an installed
libunistring.  If found, it sets and AC_SUBSTs @code{HAVE_LIBUNISTRING=yes}
and the @code{LIBUNISTRING} and @code{LTLIBUNISTRING} variables and augments
the @code{CPPFLAGS} variable, and defines the C macro
@code{HAVE_LIBUNISTRING} to 1.  Otherwise, it sets and AC_SUBSTs
@code{HAVE_LIBUNISTRING=no} and @code{LIBUNISTRING} and @code{LTLIBUNISTRING}
to empty.

The complexities that @code{gl_LIBUNISTRING} deals with are the following:

@itemize @bullet
@item
On some operating systems, in some configurations, libunistring depends
on @code{libiconv}, and the options for linking with libiconv must be
mentioned explicitly on the link command line.

@item
GNU @code{libunistring}, if installed, is not necessarily already in the
search path (@code{CPPFLAGS} for the include file search path,
@code{LDFLAGS} for the library search path).

@item
GNU @code{libunistring}, if installed, is not necessarily already in the
run time library search path.  To avoid the need for setting an environment
variable like @code{LD_LIBRARY_PATH}, the macro adds the appropriate
run time search path options to the @code{LIBUNISTRING} variable.  This works
on most systems.
@end itemize

@node Reporting problems
@section Reporting problems

@cindex bug reports
@cindex bug tracker
@cindex mailing list
If you encounter any problem, please don't hesitate to submit a detailed
bug report either in the bug tracker at the project page
@url{https://savannah.gnu.org/projects/libunistring}, or by email
to the @code{bug-libunistring@@gnu.org} mailing list.

Please always include the version number of this library, and a short
description of your operating system and compilation environment with
corresponding version numbers.

For problems that appear while building and installing @code{libunistring},
for which you don't find the remedy in the @file{INSTALL} file, please include
a description of the options that you passed to the @samp{configure} script.

@node More functionality
@chapter More advanced functionality

@cindex bidirectional reordering
For bidirectional reordering of strings, we recommend the GNU FriBidi library:
@url{http://www.fribidi.org/}.

@cindex rendering
For the rendering of Unicode strings outside of the context of a given toolkit
(KDE/Qt or GNOME/Gtk), we recommend the Pango library:
@url{https://www.pango.org/}.

@include wchar_t.texi

@include char32_t.texi

@node Licenses
@appendix Licenses
@cindex Licenses

The files of this package are covered by the licenses indicated in each
particular file or directory.  Here is a summary:

@itemize @bullet
@item
The @code{libunistring} library and its header files are dual-licensed under
"the GNU LGPLv3+ or the GNU GPLv2+". This means, you can use it under either
@itemize @bullet
@item @minus{}
the terms of the GNU Lesser General Public License (LGPL) version 3 or
(at your option) any later version, or
@item @minus{}
the terms of the GNU General Public License (GPL) version 2 or
(at your option) any later version, or
@item @minus{}
the same dual license "the GNU LGPLv3+ or the GNU GPLv2+".
@end itemize
You find the GNU LGPL version 3 in @ref{GNU LGPL}.  This license is
based on the GNU GPL version 3, see @ref{GNU GPL}.
@*
You can find the GNU GPL version 2 at
@url{https://www.gnu.org/licenses/old-licenses/gpl-2.0.html}.
@*
Note: This dual license makes it possible for the @code{libunistring} library
to be used by packages under GPLv2 or GPLv2+ licenses, in particular. See
the table in @url{https://www.gnu.org/licenses/gpl-faq.html#AllCompatibility}.


@item
This manual is free documentation.  It is dually licensed under the
GNU FDL and the GNU GPL.  This means that you can redistribute this
manual under either of these two licenses, at your choice.
@*
This manual is covered by the GNU FDL.  Permission is granted to copy,
distribute and/or modify this document under the terms of the
GNU Free Documentation License (FDL), either version 1.2 of the
License, or (at your option) any later version published by the
Free Software Foundation (FSF); with no Invariant Sections, with no
Front-Cover Text, and with no Back-Cover Texts.
A copy of the license is included in @ref{GNU FDL}.
@*
This manual is covered by the GNU GPL.  You can redistribute it and/or
modify it under the terms of the GNU General Public License (GPL), either
version 3 of the License, or (at your option) any later version published
by the Free Software Foundation (FSF).
A copy of the license is included in @ref{GNU GPL}.
@end itemize

@menu
* GNU GPL::                     GNU General Public License
* GNU LGPL::                    GNU Lesser General Public License
* GNU FDL::                     GNU Free Documentation License
@end menu

@page
@node GNU GPL
@appendixsec GNU GENERAL PUBLIC LICENSE
@cindex GPL, GNU General Public License
@cindex License, GNU GPL
@include gpl.texi
@page
@node GNU LGPL
@appendixsec GNU LESSER GENERAL PUBLIC LICENSE
@cindex LGPL, GNU Lesser General Public License
@cindex License, GNU LGPL
@include lgpl.texi
@page
@node GNU FDL
@appendixsec GNU Free Documentation License
@cindex FDL, GNU Free Documentation License
@cindex License, GNU FDL
@include fdl.texi

@node Index
@unnumbered Index

@printindex cp

@bye

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