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	<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html401/loose.dtd">
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	<head>
	<title>GNU libtextstyle: 3. The programmer's perspective</title>

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	<tr><td valign="middle" align="left">[<a href="libtextstyle_2.html#SEC4" title="Beginning of this chapter or previous chapter"> << </a>]</td>
	<td valign="middle" align="left">[<a href="libtextstyle_4.html#SEC37" title="Next chapter"> >> </a>]</td>
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	<td valign="middle" align="left">[<a href="libtextstyle_toc.html#SEC_Top" title="Cover (top) of document">Top</a>]</td>
	<td valign="middle" align="left">[<a href="libtextstyle_toc.html#SEC_Contents" title="Table of contents">Contents</a>]</td>
	<td valign="middle" align="left">[<a href="libtextstyle_5.html#SEC45" title="Index">Index</a>]</td>
	<td valign="middle" align="left">[<a href="libtextstyle_abt.html#SEC_About" title="About (help)"> ? </a>]</td>
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	<hr size="2">
	<a name="The-programmer_0027s-view"></a>
	<a name="SEC15"></a>
	<h1 class="chapter"> <a href="libtextstyle_toc.html#TOC15">3. The programmer's perspective</a> </h1>

	<p>As a programmer, enabling styling consists of the following tasks:
	</p><ol>
	<li>
	Define the command-line options and environment variable that the user
	can use to control the styling.
	</li><li>
	Define the CSS classes that the user can use in the CSS file. Each CSS
	class corresponds to a text role; each CSS class can be given a different
	styling by the user.
	</li><li>
	Change the output routines so that they take an ‘<samp>ostream_t</samp>’ object
	as argument instead of a ‘<samp>FILE *</samp>’.
	</li><li>
	Insert paired invocations to <code>styled_ostream_begin_css_class</code>,
	<code>styled_ostream_end_css_class</code> around each run of text with a
	specific text role.
	</li><li>
	Link with <code>libtextstyle</code>. If your package is using GNU autoconf,
	you can use the <code>libtextstyle.m4</code> macro from Gnulib.
	</li><li>
	Prepare a default style file.
	</li><li>
	Update the documentation of your package.
	</li></ol>

	<p>The following sections go into more detail.
	</p>


	<a name="Basic-use"></a>
	<a name="SEC16"></a>
	<h2 class="section"> <a href="libtextstyle_toc.html#TOC16">3.1 Basic use of libtextstyle</a> </h2>

	<p>Source code that makes use of GNU libtextstyle needs an include statement:
	</p>
	<table><tr><td> </td><td><pre class="smallexample">#include <textstyle.h>
	</pre></td></tr></table>

	<p>Basic use of GNU libtextstyle consists of statements like these:
	</p>
	<table><tr><td> </td><td><pre class="smallexample"> styled_ostream_t stream =
	styled_ostream_create (STDOUT_FILENO, "(stdout)", TTYCTL_AUTO,
	style_file_name);
	...
	styled_ostream_begin_use_class (stream, css_class);
	...
	ostream_write_str (stream, string);
	...
	styled_ostream_end_use_class (stream, css_class);
	...
	styled_ostream_free (stream);
	</pre></td></tr></table>

	<p>Before this snippet, your code needs to determine the name of the style
	file to use (<code>style_file_name</code>). If no styling is desired – the
	precise condition depends on the value of <code>color_mode</code> but also on
	your application logic –, you should set <code>style_file_name</code> to
	<code>NULL</code>.
	</p>
	<p>An object of type <code>styled_ostream_t</code> is allocated. The function
	<code>styled_ostream_create</code> allocates it; the function
	<code>styled_ostream_free</code> deallocates it.
	</p>
	<p>Such <code>styled_ostream_t</code> supports output operations
	(<code>ostream_write_str</code>), interleaved with adding and removing CSS
	classes. The CSS class in effect when an output operation is performed
	determines, through the style file, the text attributes associated with
	that piece of text.
	</p>


	<a name="Hyperlinks"></a>
	<a name="SEC17"></a>
	<h3 class="subsection"> <a href="libtextstyle_toc.html#TOC17">3.1.1 Hyperlinks</a> </h3>

	<p>Text output may contain hyperlinks. These hyperlinks are encoded through
	an escape sequence, specified at
	<a href="https://gist.github.com/egmontkob/eb114294efbcd5adb1944c9f3cb5feda">Hyperlinks in terminal emulators</a>. Currently (as of 2019), they are
	displayed only in <code>gnome-terminal</code> version 3.26 or above. More
	terminal emulators will support hyperlinks in the future. Terminal
	emulators which don't support hyperlinks ignore it, except for a few
	terminal emulators, for which users may need to disable the hyperlinks
	(see <a href="libtextstyle_2.html#SEC9">The environment variable <code>NO_TERM_HYPERLINKS</code></a>) if the heuristic built into
	<code>libtextstyle</code> does not already disable them.
	</p>
	<p>To emit a hyperlink, use code like this:
	</p>
	<table><tr><td> </td><td><pre class="smallexample"> styled_ostream_t stream = ...
	...
	/* Start a hyperlink. */
	styled_ostream_set_hyperlink (stream, url, NULL);
	...
	/* Emit the anchor text. This can be styled text. */
	ostream_write_str (stream, "Click here!");
	...
	/* End the current hyperlink. */
	styled_ostream_set_hyperlink (stream, NULL, NULL);
	</pre></td></tr></table>

	<p>The anchor text can be styled. But the hyperlinks themselves cannot be
	styled; they behave as implemented by the terminal emulator.
	</p>

	<a name="Include-files"></a>
	<a name="SEC18"></a>
	<h2 class="section"> <a href="libtextstyle_toc.html#TOC18">3.2 Include files</a> </h2>

	<p>The include file <code><textstyle.h></code> declares all facilities defined by
	the library.
	</p>

	<a name="Link-options"></a>
	<a name="SEC19"></a>
	<h2 class="section"> <a href="libtextstyle_toc.html#TOC19">3.3 Link options</a> </h2>

	<p>The library to link with is called <code>libtextstyle</code>, with a
	system-dependent suffix. You link with it though link options of the
	form <code>-ltextstyle</code> for a library installed in system locations, or
	<code>-L<var>libdir</var> -ltextstyle</code> for a static library installed in other
	locations, or <code>-L<var>libdir</var> -ltextstyle -Wl,-rpath,<var>libdir</var></code>
	for a shared library installed in other locations (assuming a GCC
	compatible compiler and linker and no <code>libtool</code>), or
	<code>-L<var>libdir</var> -ltextstyle -R<var>libdir</var></code> for a shared library
	installed in other locations (with <code>libtool</code>). Additionally, the
	link options may need to include the dependencies: <code>-lm</code>, and
	<code>-lncurses</code> or (on NetBSD) <code>-ltermcap</code> or (on AIX)
	<code>-lxcurses</code> or (on HP-UX) <code>-lcurses</code>, and on some systems also
	<code>-liconv</code>.
	</p>
	<p>It is a bit complicated to determine the right link options in a portable
	way. Therefore an Autoconf macro is provided in the file
	<code>libtextstyle.m4</code> in Gnulib, that makes this task easier. Assuming
	the build system of your package is based on GNU Autoconf, you invoke it
	through <code>gl_LIBTEXTSTYLE</code>. It searches for an installed
	<code>libtextstyle</code>. If found, it sets and AC_SUBSTs
	<code>HAVE_LIBTEXTSTYLE=yes</code> and the <code>LIBTEXTSTYLE</code> and
	<code>LTLIBTEXTSTYLE</code> variables, and augments the <code>CPPFLAGS</code>
	variable, and #defines <code>HAVE_LIBTEXTSTYLE</code> to 1. Otherwise, it sets
	and AC_SUBSTs <code>HAVE_LIBTEXTSTYLE=no</code> and <code>LIBTEXTSTYLE</code> and
	<code>LTLIBTEXTSTYLE</code> to empty. In link commands that use <code>libtool</code>,
	use <code>LTLIBTEXTSTYLE</code>; in link commands that don't use <code>libtool</code>,
	use <code>LIBTEXTSTYLE</code>.
	</p>
	<p>If you use GNU Automake, the proper place to use the link options is
	<code><var>program</var>_LDADD</code> for programs and <code><var>library</var>_LIBADD</code>
	for libraries.
	</p>

	<a name="Command_002dline-options"></a>
	<a name="SEC20"></a>
	<h2 class="section"> <a href="libtextstyle_toc.html#TOC20">3.4 Command-line options</a> </h2>

	<p>While you are free to provide any command-line option to enable the
	styling of the output, it is good if different GNU programs use the same
	command-line options for this purpose. These options are described in
	the sections <a href="libtextstyle_2.html#SEC11">The <code>--color</code> option</a> and <a href="libtextstyle_2.html#SEC12">The <code>--style</code> option</a>. To
	achieve this, use the following API (declared in <code><textstyle.h></code>):
	</p>
	<dl>
	<dt><u>Variable:</u> bool <b>color_test_mode</b>
	<a name="IDX1"></a>
	</dt>
	<dd><p>True if a <code>--color</code> option with value <code>test</code> has been seen.
	</p></dd></dl>

	<dl>
	<dt><u>Variable:</u> enum color_option <b>color_mode</b>
	<a name="IDX2"></a>
	</dt>
	<dd><p>Stores the value of the <code>--color</code> option.
	</p></dd></dl>

	<dl>
	<dt><u>Variable:</u> const char * <b>style_file_name</b>
	<a name="IDX3"></a>
	</dt>
	<dd><p>Stores the value of the <code>--style</code> option.
	</p></dd></dl>

	<p>Note: These variables, like any variables exported from shared libraries,
	can only be used in executable code. You <em>cannot</em> portably use
	their address in initializers of global or static variables. This is a
	restriction that is imposed by the Windows, Cygwin, and Android platforms.
	</p>
	<dl>
	<dt><u>Function:</u> bool <b>handle_color_option</b><i> (const char *<var>option</var>)</i>
	<a name="IDX4"></a>
	</dt>
	<dd><p>You invoke this function when, during argument parsing, you have
	encountered a <code>--color</code> or <code>--color=...</code> option. The return
	value is an error indicator: <code>true</code> means an invalid option.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> void <b>handle_style_option</b><i> (const char *<var>option</var>)</i>
	<a name="IDX5"></a>
	</dt>
	<dd><p>You invoke this function when, during argument parsing, you have
	encountered a <code>--style</code> or <code>--style=...</code> option.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> void <b>print_color_test</b><i> (void)</i>
	<a name="IDX6"></a>
	</dt>
	<dd><p>Prints a color test page. You invoke this function after argument
	parsing, when the <code>color_test_mode</code> variable is true.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> void <b>style_file_prepare</b><i> (const char <var>style_file_envvar</var>, const char <var>stylesdir_envvar</var>, const char <var>stylesdir_after_install</var>, const char <var>default_style_file</var>)</i>
	<a name="IDX7"></a>
	</dt>
	<dd><p>Assigns a default value to <code>style_file_name</code> if necessary. You
	invoke this function after argument parsing, when <code>color_test_mode</code>
	is false.
	</p>
	<p><code><var>style_file_envvar</var></code> is an environment variable that, when set
	to a non-empty value, specifies the style file to use. This environment
	variable is meant to be set by the user.
	</p>
	<p><code><var>stylesdir_envvar</var></code> is an environment variable that, when set
	to a non-empty value, specifies the directory with the style files, or
	<code>NULL</code>. This is necessary for running the testsuite before
	‘<samp>make install</samp>’.
	</p>
	<p><code><var>stylesdir_after_install</var></code> is the directory with the style
	files after ‘<samp>make install</samp>’.
	</p>
	<p><code><var>default_style_file</var></code> is the file name of the default style
	file, relative to <var>stylesdir</var>.
	</p></dd></dl>


	<a name="The-output-stream-hierarchy"></a>
	<a name="SEC21"></a>
	<h2 class="section"> <a href="libtextstyle_toc.html#TOC21">3.5 The output stream hierarchy</a> </h2>

	<p>There are various classes of output streams, some of them with styling
	support. These “classes” are defined in an object-oriented programming
	style that resembles C++ or Java, but are actually implemented in C with
	a little bit of object orientation syntax. These definitions are
	preprocessed down to C. As a consequence, GNU libtextstyle is a C
	library and does not need to link with the C++ standard library.
	</p>
	<p>All these classes are declared in <code><textstyle.h></code>.
	</p>
	<p>The base output stream type is ‘<samp>ostream_t</samp>’. It is a pointer type to
	a (hidden) implementation type. Similarly for the subclasses.
	</p>
	<p>When we say that ‘<samp>some_ostream_t</samp>’ is a subclass of ‘<samp>ostream_t</samp>’,
	what we mean is:
	</p><ul>
	<li>
	Every ‘<samp>some_ostream_t</samp>’ object can be converted to an
	‘<samp>ostream_t</samp>’, by virtue of a simple assignment. No cast is needed.
	</li><li>
	The opposite conversion, from ‘<samp>ostream_t</samp>’ to ‘<samp>some_ostream_t</samp>’,
	can also be performed, provided that the object is actually an instance
	of ‘<samp>some_ostream_t</samp>’.
	</li><li>
	Every method ‘<samp>ostream_<var>foobar</var></samp>’ exists also as a method
	‘<samp>some_ostream_<var>foobar</var></samp>’ with compatible argument types and a
	compatible return type.
	</li></ul>



	<a name="The-ostream-class"></a>
	<a name="SEC22"></a>
	<h3 class="subsection"> <a href="libtextstyle_toc.html#TOC22">3.5.1 The abstract <code>ostream</code> class</a> </h3>

	<p>The base output stream type is ‘<samp>ostream_t</samp>’.
	</p>
	<p>It has the following methods:
	</p>
	<dl>
	<dt><u>Function:</u> void <b>ostream_write_mem</b><i> (ostream_t <var>stream</var>, const void *<var>data</var>, size_t <var>len</var>)</i>
	<a name="IDX8"></a>
	</dt>
	<dd><p>Writes a sequence of bytes to a stream.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> void <b>ostream_write_str</b><i> (ostream_t <var>stream</var>, const char *<var>string</var>)</i>
	<a name="IDX9"></a>
	</dt>
	<dd><p>Writes a string's contents to a stream.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> ptrdiff_t <b>ostream_printf</b><i> (ostream_t <var>stream</var>, const char *<var>format</var>, ...)</i>
	<a name="IDX10"></a>
	</dt>
	<dt><u>Function:</u> ptrdiff_t <b>ostream_vprintf</b><i> (ostream_t <var>stream</var>, const char *<var>format</var>, va_list args)</i>
	<a name="IDX11"></a>
	</dt>
	<dd><p>Writes formatted output to a stream.
	</p>
	<p>These functions return the size of formatted output, or a negative value
	in case of an error.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> void <b>ostream_flush</b><i> (ostream_t <var>stream</var>, ostream_flush_scope_t <var>scope</var>)</i>
	<a name="IDX12"></a>
	</dt>
	<dd><p>Brings buffered data to its destination.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> void <b>ostream_free</b><i> (ostream_t <var>stream</var>)</i>
	<a name="IDX13"></a>
	</dt>
	<dd><p>Closes and frees a stream.
	</p></dd></dl>


	<a name="The-styled_005fostream-class"></a>
	<a name="SEC23"></a>
	<h3 class="subsection"> <a href="libtextstyle_toc.html#TOC23">3.5.2 The abstract <code>styled_ostream</code> class</a> </h3>

	<p>The type for a styled output stream is ‘<samp>styled_ostream_t</samp>’. It is a
	subclass of ‘<samp>ostream_t</samp>’ that adds the following methods:
	</p>
	<dl>
	<dt><u>Function:</u> void <b>styled_ostream_begin_use_class</b><i> (styled_ostream_t <var>stream</var>, const char *<var>classname</var>)</i>
	<a name="IDX14"></a>
	</dt>
	<dd><p>Starts a run of text belonging to <code><var>classname</var></code>. The
	<code><var>classname</var></code> is the name of a CSS class. It can be chosen
	arbitrarily and customized through the CSS file.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> void <b>styled_ostream_end_use_class</b><i> (styled_ostream_t <var>stream</var>, const char *<var>classname</var>)</i>
	<a name="IDX15"></a>
	</dt>
	<dd><p>Ends a run of text belonging to <code><var>classname</var></code>. The
	<code>styled_ostream_begin_use_class</code> /
	<code>styled_ostream_end_use_class</code> calls must match properly.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> const char * <b>styled_ostream_get_hyperlink_ref</b><i> (styled_ostream_t <var>stream</var>)</i>
	<a name="IDX16"></a>
	</dt>
	<dd><p>Returns the referred URL of the currently set hyperlink, or <code>NULL</code>
	if no hyperlink attribute is currently set.
	</p>
	<p>Note: The returned string is only valid up to the next invocation of
	<code>styled_ostream_set_hyperlink</code>.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> const char * <b>styled_ostream_get_hyperlink_id</b><i> (styled_ostream_t <var>stream</var>)</i>
	<a name="IDX17"></a>
	</dt>
	<dd><p>Returns the id of the currently set hyperlink, or <code>NULL</code> if no
	hyperlink attribute is currently set.
	</p>
	<p>Note: The returned string is only valid up to the next invocation of
	<code>styled_ostream_set_hyperlink</code>.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> void <b>styled_ostream_set_hyperlink</b><i> (styled_ostream_t <var>stream</var>, const char <var>ref</var>, const char <var>id</var>)</i>
	<a name="IDX18"></a>
	</dt>
	<dd><p>Sets or removes a hyperlink attribute.
	</p>
	<p>To set a hyperlink attribute, pass a non-<code>NULL</code> <var>ref</var>.
	<var>ref</var> is an URL; it should be at most 2083 bytes long. Non-ASCII
	characters should be URI-escaped (using the %nn syntax). <var>id</var> is
	an optional identifier. On terminal output, multiple hyperlinks with
	the same <var>id</var> will be highlighted together. If specified, <var>id</var>
	should be at most 250 bytes long.
	</p>
	<p>To remove a hyperlink attribute, pass <code>NULL</code> for <var>ref</var> and <var>id</var>.
	</p>
	<p>Hyperlinks don't nest. That is, a hyperlink attribute is enabled only
	up to the next invocation of <code>styled_ostream_set_hyperlink</code>.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> void <b>styled_ostream_flush_to_current_style</b><i> (styled_ostream_t <var>stream</var>)</i>
	<a name="IDX19"></a>
	</dt>
	<dd><p>This function acts like <code>ostream_flush (<var>stream</var>, FLUSH_THIS_STREAM)</code>,
	except that it leaves the destination with the current text style enabled,
	instead of with the default text style.
	</p>
	<p>After calling this function, you can output strings without newlines(!) to the
	underlying stream, and they will be rendered like strings passed to
	<code>ostream_write_mem</code>, <code>ostream_write_str</code>, or <code>ostream_printf</code>.
	</p></dd></dl>


	<a name="ostream-subclasses-without-styling"></a>
	<a name="SEC24"></a>
	<h3 class="subsection"> <a href="libtextstyle_toc.html#TOC24">3.5.3 Concrete ostream subclasses without styling</a> </h3>



	<a name="The-file_005fostream-class"></a>
	<a name="SEC25"></a>
	<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC25">3.5.3.1 The <code>file_ostream</code> class</a> </h4>

	<p>The <code>file_ostream</code> class supports output to an <code><stdio.h></code>
	<code>FILE</code> stream. Its type is ‘<samp>file_ostream_t</samp>’. It is a subclass
	of ‘<samp>ostream_t</samp>’ that adds no methods.
	</p>
	<p>It can be instantiated through this function:
	</p>
	<dl>
	<dt><u>Function:</u> file_ostream_t <b>file_ostream_create</b><i> (FILE *<var>fp</var>)</i>
	<a name="IDX20"></a>
	</dt>
	<dd><p>Creates an output stream referring to <code><var>fp</var></code>.
	</p>
	<p>Note: The resulting stream must be closed before <code><var>fp</var></code> can be
	closed.
	</p></dd></dl>


	<a name="The-fd_005fostream-class"></a>
	<a name="SEC26"></a>
	<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC26">3.5.3.2 The <code>fd_ostream</code> class</a> </h4>

	<p>The <code>file_ostream</code> class supports output to a file descriptor. Its
	type is ‘<samp>fd_ostream_t</samp>’. It is a subclass of ‘<samp>ostream_t</samp>’ that
	adds no methods.
	</p>
	<p>It can be instantiated through this function:
	</p>
	<dl>
	<dt><u>Function:</u> fd_ostream_t <b>fd_ostream_create</b><i> (int <var>fd</var>, const char *<var>filename</var>, bool <var>buffered</var>)</i>
	<a name="IDX21"></a>
	</dt>
	<dd><p>Creates an output stream referring to the file descriptor <code><var>fd</var></code>.
	</p>
	<p><code><var>filename</var></code> is used only for error messages.
	</p>
	<p>Note: The resulting stream must be closed before <code><var>fd</var></code> can be
	closed.
	</p></dd></dl>


	<a name="The-term_005fostream-class"></a>
	<a name="SEC27"></a>
	<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC27">3.5.3.3 The <code>term_ostream</code> class</a> </h4>

	<p>The <code>term_ostream</code> class supports output to a file descriptor that
	is connected to a terminal emulator or console. Its type is
	‘<samp>term_ostream_t</samp>’. It is a subclass of ‘<samp>ostream_t</samp>’.
	</p>
	<p>It can be instantiated through this function:
	</p>
	<dl>
	<dt><u>Function:</u> term_ostream_t <b>term_ostream_create</b><i> (int <var>fd</var>, const char *<var>filename</var>, ttyctl_t <var>tty_control</var>)</i>
	<a name="IDX22"></a>
	</dt>
	<dd><p>Creates an output stream referring to the file descriptor <code><var>fd</var></code>.
	</p>
	<p><code><var>filename</var></code> is used only for error messages.
	</p>
	<p><code><var>tty_control</var></code> specifies the amount of control to take over the
	underlying tty.
	</p>
	<p>The resulting stream will be line-buffered.
	</p>
	<p>Note: The resulting stream must be closed before <code><var>fd</var></code> can be
	closed.
	</p></dd></dl>

	<p>The class adds the following methods:
	</p>
	<dl>
	<dt><u>Function:</u> term_color_t <b>term_ostream_rgb_to_color</b><i> (term_ostream_t <var>stream</var>, int <var>red</var>, int <var>green</var>, int <var>blue</var>)</i>
	<a name="IDX23"></a>
	</dt>
	<dd><p>Converts an RGB value
	(<code><var>red</var></code>, <code><var>green</var></code>, <code><var>blue</var></code> in [0..255]) to
	a color, valid for this stream only.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> term_color_t <b>term_ostream_get_color</b><i> (term_ostream_t <var>stream</var>)</i>
	<a name="IDX24"></a>
	</dt>
	<dt><u>Function:</u> void <b>term_ostream_set_color</b><i> (term_ostream_t <var>stream</var>, term_color_t <var>color</var>)</i>
	<a name="IDX25"></a>
	</dt>
	<dd><p>Gets/sets the text color.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> term_color_t <b>term_ostream_get_bgcolor</b><i> (term_ostream_t <var>stream</var>)</i>
	<a name="IDX26"></a>
	</dt>
	<dt><u>Function:</u> void <b>term_ostream_set_bgcolor</b><i> (term_ostream_t <var>stream</var>, term_color_t <var>color</var>)</i>
	<a name="IDX27"></a>
	</dt>
	<dd><p>Gets/sets the background color.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> term_weight_t <b>term_ostream_get_weight</b><i> (term_ostream_t <var>stream</var>)</i>
	<a name="IDX28"></a>
	</dt>
	<dt><u>Function:</u> void <b>term_ostream_set_weight</b><i> (term_ostream_t <var>stream</var>, term_weight_t <var>weight</var>)</i>
	<a name="IDX29"></a>
	</dt>
	<dd><p>Gets/sets the font weight.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> term_posture_t <b>term_ostream_get_posture</b><i> (term_ostream_t <var>stream</var>)</i>
	<a name="IDX30"></a>
	</dt>
	<dt><u>Function:</u> void <b>term_ostream_set_posture</b><i> (term_ostream_t <var>stream</var>, term_posture_t <var>posture</var>)</i>
	<a name="IDX31"></a>
	</dt>
	<dd><p>Gets/sets the font posture.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> term_underline_t <b>term_ostream_get_underline</b><i> (term_ostream_t <var>stream</var>)</i>
	<a name="IDX32"></a>
	</dt>
	<dt><u>Function:</u> void <b>term_ostream_set_underline</b><i> (term_ostream_t <var>stream</var>, term_underline_t <var>underline</var>)</i>
	<a name="IDX33"></a>
	</dt>
	<dd><p>Gets/sets the text underline decoration.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> const char * <b>term_ostream_get_hyperlink_ref</b><i> (term_ostream_t <var>stream</var>)</i>
	<a name="IDX34"></a>
	</dt>
	<dd><p>Returns the referred URL of the currently set hyperlink, or <code>NULL</code>
	if no hyperlink attribute is currently set.
	</p>
	<p>Note: The returned string is only valid up to the next invocation of
	<code>term_ostream_set_hyperlink</code>.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> const char * <b>term_ostream_get_hyperlink_id</b><i> (term_ostream_t <var>stream</var>)</i>
	<a name="IDX35"></a>
	</dt>
	<dd><p>Returns the id of the currently set hyperlink, or <code>NULL</code> if no
	hyperlink attribute is currently set.
	</p>
	<p>Note: The returned string is only valid up to the next invocation of
	<code>term_ostream_set_hyperlink</code>.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> void <b>term_ostream_set_hyperlink</b><i> (term_ostream_t <var>stream</var>, const char <var>ref</var>, const char <var>id</var>)</i>
	<a name="IDX36"></a>
	</dt>
	<dd><p>Sets or removes a hyperlink attribute.
	</p>
	<p>To set a hyperlink attribute, pass a non-<code>NULL</code> <var>ref</var>.
	<var>ref</var> is an URL; it should be at most 2083 bytes long. Non-ASCII
	characters should be URI-escaped (using the %nn syntax). <var>id</var> is
	an optional identifier. Multiple hyperlinks with the same <var>id</var>
	will be highlighted together. If specified, <var>id</var> should be at most
	250 bytes long.
	</p>
	<p>To remove a hyperlink attribute, pass <code>NULL</code> for <var>ref</var> and <var>id</var>.
	</p>
	<p>Hyperlinks don't nest. That is, a hyperlink attribute is enabled only
	up to the next invocation of <code>styled_ostream_set_hyperlink</code>.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> void <b>term_ostream_flush_to_current_style</b><i> (term_ostream_t <var>stream</var>)</i>
	<a name="IDX37"></a>
	</dt>
	<dd><p>This function acts like <code>ostream_flush (<var>stream</var>, FLUSH_THIS_STREAM)</code>,
	except that it leaves the terminal with the current text attributes enabled,
	instead of with the default text attributes.
	</p>
	<p>After calling this function, you can output strings without newlines(!) to the
	underlying file descriptor, and they will be rendered like strings passed to
	<code>ostream_write_mem</code>, <code>ostream_write_str</code>, or <code>ostream_printf</code>.
	</p></dd></dl>


	<a name="The-html_005fostream-class"></a>
	<a name="SEC28"></a>
	<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC28">3.5.3.4 The <code>html_ostream</code> class</a> </h4>

	<p>The <code>html_ostream</code> class supports output to any destination, in HTML
	syntax. Its type is ‘<samp>html_ostream_t</samp>’. It is a subclass of
	‘<samp>ostream_t</samp>’.
	</p>
	<p>It can be instantiated through this function:
	</p>
	<dl>
	<dt><u>Function:</u> html_ostream_t <b>html_ostream_create</b><i> (ostream_t <var>destination</var>)</i>
	<a name="IDX38"></a>
	</dt>
	<dd><p>Creates an output stream that takes input in the UTF-8 encoding and
	writes it in HTML form on <code><var>destination</var></code>.
	</p>
	<p>This stream produces a sequence of lines. The caller is responsible for
	opening the <code><body><html></code> elements before and for closing them
	after the use of this stream.
	</p>
	<p>Note: The resulting stream must be closed before <code><var>destination</var></code>
	can be closed.
	</p></dd></dl>

	<p>The class adds the following methods:
	</p>
	<dl>
	<dt><u>Function:</u> void <b>html_ostream_begin_span</b><i> (html_ostream_t <var>stream</var>, const char *<var>classname</var>)</i>
	<a name="IDX39"></a>
	</dt>
	<dd><p>Starts a <code><span class="<var>classname</var>"></code> element. The
	<code><var>classname</var></code> is the name of a CSS class. It can be chosen
	arbitrarily and customized through the CSS file.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> void <b>html_ostream_end_span</b><i> (html_ostream_t <var>stream</var>, const char *<var>classname</var>)</i>
	<a name="IDX40"></a>
	</dt>
	<dd><p>Ends a <code><span class="<var>classname</var>"></code> element.
	</p>
	<p>The <code>html_ostream_begin_span</code> / <code>html_ostream_end_span</code> calls
	must match properly.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> const char * <b>html_ostream_get_hyperlink_ref</b><i> (html_ostream_t <var>stream</var>)</i>
	<a name="IDX41"></a>
	</dt>
	<dd><p>Returns the referred URL of the currently set hyperlink, or <code>NULL</code>
	if no hyperlink attribute is currently set.
	</p>
	<p>Note: The returned string is only valid up to the next invocation of
	<code>html_ostream_set_hyperlink_ref</code>.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> void <b>html_ostream_set_hyperlink_ref</b><i> (html_ostream_t <var>stream</var>, const char *<var>ref</var>)</i>
	<a name="IDX42"></a>
	</dt>
	<dd><p>Sets or removes a hyperlink attribute.
	</p>
	<p>To set a hyperlink attribute, pass a non-<code>NULL</code> <var>ref</var>.
	<var>ref</var> is an URL; it should be at most 2083 bytes long. Non-ASCII
	characters should be URI-escaped (using the %nn syntax).
	</p>
	<p>To remove a hyperlink attribute, pass <code>NULL</code> for <var>ref</var>.
	</p>
	<p>Hyperlinks don't nest. That is, a hyperlink attribute is enabled only
	up to the next invocation of <code>html_ostream_set_hyperlink_ref</code>.
	</p></dd></dl>

	<dl>
	<dt><u>Function:</u> void <b>html_ostream_flush_to_current_style</b><i> (html_ostream_t <var>stream</var>)</i>
	<a name="IDX43"></a>
	</dt>
	<dd><p>This function acts like <code>ostream_flush (<var>stream</var>, FLUSH_THIS_STREAM)</code>,
	except that it leaves the destination with the current text style enabled,
	instead of with the default text style.
	</p>
	<p>After calling this function, you can output strings without newlines(!) to the
	underlying stream, and they will be rendered like strings passed to
	<code>ostream_write_mem</code>, <code>ostream_write_str</code>, or <code>ostream_printf</code>.
	</p></dd></dl>


	<a name="The-memory_005fostream-class"></a>
	<a name="SEC29"></a>
	<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC29">3.5.3.5 The <code>memory_ostream</code> class</a> </h4>

	<p>The <code>memory_ostream</code> class supports output to an in-memory buffer.
	Its type is ‘<samp>memory_ostream_t</samp>’. It is a subclass of
	‘<samp>ostream_t</samp>’.
	</p>
	<p>It can be instantiated through this function:
	</p>
	<dl>
	<dt><u>Function:</u> memory_ostream_t <b>memory_ostream_create</b><i> (void)</i>
	<a name="IDX44"></a>
	</dt>
	<dd><p>Creates an output stream that accumulates the output in a memory buffer.
	</p></dd></dl>

	<p>The class adds the following method:
	</p>
	<dl>
	<dt><u>Function:</u> void <b>memory_ostream_contents</b><i> (memory_ostream_t <var>stream</var>, const void *<var>bufp</var>, size_t <var>buflenp</var>)</i>
	<a name="IDX45"></a>
	</dt>
	<dd><p>Returns a pointer to the output accumulated so far and its size. It
	stores them in <code><var>bufp</var></code> and <code><var>buflenp</var></code>, respectively.
	</p>
	<p>Note: These two return values become invalid when more output is done to
	the stream or when the stream is freed.
	</p></dd></dl>


	<a name="The-iconv_005fostream-class"></a>
	<a name="SEC30"></a>
	<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC30">3.5.3.6 The <code>iconv_ostream</code> class</a> </h4>

	<p>The <code>iconv_ostream</code> class supports output to any destination. Its
	type is ‘<samp>iconv_ostream_t</samp>’. It is a subclass of ‘<samp>ostream_t</samp>’
	that adds no methods.
	</p>
	<p>It can be instantiated through this function:
	</p>
	<dl>
	<dt><u>Function:</u> iconv_ostream_t <b>iconv_ostream_create</b><i> (const char <var>from_encoding</var>, const char <var>to_encoding</var>, ostream_t <var>destination</var>)</i>
	<a name="IDX46"></a>
	</dt>
	<dd><p>Creates an output stream that converts from <code><var>from_encoding</var></code> to
	<code><var>to_encoding</var></code>, writing the result to <code><var>destination</var></code>.
	</p>
	<p>Note: The resulting stream must be closed before <code><var>destination</var></code>
	can be closed.
	</p></dd></dl>


	<a name="styled_005fostream-subclasses"></a>
	<a name="SEC31"></a>
	<h3 class="subsection"> <a href="libtextstyle_toc.html#TOC31">3.5.4 Concrete <code>styled_ostream</code> subclasses</a> </h3>



	<a name="The-term_005fstyled_005fostream-class"></a>
	<a name="SEC32"></a>
	<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC32">3.5.4.1 The <code>term_styled_ostream</code> class</a> </h4>

	<p>The <code>term_styled_ostream</code> class supports styled output to a file
	descriptor that is connected to a terminal emulator or console. Its type
	is ‘<samp>term_styled_ostream_t</samp>’. It is a subclass of
	‘<samp>styled_ostream_t</samp>’.
	</p>
	<p>It can be instantiated through this function:
	</p>
	<dl>
	<dt><u>Function:</u> term_styled_ostream_t <b>term_styled_ostream_create</b><i> (int <var>fd</var>, const char <var>filename</var>, ttyctl_t <var>tty_control</var>, const char <var>css_filename</var>)</i>
	<a name="IDX47"></a>
	</dt>
	<dd><p>Creates an output stream referring to the file descriptor <code><var>fd</var></code>,
	styled with the file <code><var>css_filename</var></code>.
	</p>
	<p><code><var>filename</var></code> is used only for error messages.
	</p>
	<p><code><var>tty_control</var></code> specifies the amount of control to take over the
	underlying tty.
	</p>
	<p>Note: The resulting stream must be closed before <code><var>fd</var></code> can be
	closed.
	</p>
	<p>Returns <code>NULL</code> upon failure.
	</p></dd></dl>

	<p>The following is a variant of this function. Upon failure, it does not
	return <code>NULL</code>; instead, it returns a styled <code>fd_stream</code> on
	which the styling operations exist but are no-ops.
	</p>
	<dl>
	<dt><u>Function:</u> styled_ostream_t <b>styled_ostream_create</b><i> (int <var>fd</var>, const char <var>filename</var>, ttyctl_t <var>tty_control</var>, const char <var>css_filename</var>)</i>
	<a name="IDX48"></a>
	</dt>
	<dd><p>Creates an output stream referring to the file descriptor <code><var>fd</var></code>,
	styled with the file <code><var>css_filename</var></code> if possible.
	</p>
	<p><code><var>filename</var></code> is used only for error messages.
	</p>
	<p><code><var>tty_control</var></code> specifies the amount of control to take over the
	underlying tty.
	</p>
	<p>Note: The resulting stream must be closed before <code><var>fd</var></code> can be
	closed.
	</p></dd></dl>


	<a name="The-html_005fstyled_005fostream-class"></a>
	<a name="SEC33"></a>
	<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC33">3.5.4.2 The <code>html_styled_ostream</code> class</a> </h4>

	<p>The <code>html_styled_ostream</code> class supports styled output to any
	destination, in HTML syntax. Its type is ‘<samp>html_styled_ostream_t</samp>’.
	It is a subclass of ‘<samp>styled_ostream_t</samp>’.
	</p>
	<p>It can be instantiated through this function:
	</p>
	<dl>
	<dt><u>Function:</u> html_styled_ostream_t <b>html_styled_ostream_create</b><i> (ostream_t <var>destination</var>, const char *<var>css_filename</var>)</i>
	<a name="IDX49"></a>
	</dt>
	<dd><p>Creates an output stream that takes input in the UTF-8 encoding and
	writes it in HTML form on <code><var>destination</var></code>, styled with the file
	<code><var>css_filename</var></code>.
	</p>
	<p>Note: The resulting stream must be closed before <code><var>destination</var></code>
	can be closed.
	</p></dd></dl>


	<a name="The-noop_005fstyled_005fostream-class"></a>
	<a name="SEC34"></a>
	<h4 class="subsubsection"> <a href="libtextstyle_toc.html#TOC34">3.5.4.3 The <code>noop_styled_ostream</code> class</a> </h4>

	<p>The <code>noop_styled_ostream</code> class supports the styled output operations
	to any destination. The text is output to the given destination; the
	styling operations, however, do nothing. Its type is
	‘<samp>noop_styled_ostream_t</samp>’. It is a subclass of ‘<samp>styled_ostream_t</samp>’.
	</p>
	<p>It can be instantiated through this function:
	</p>
	<dl>
	<dt><u>Function:</u> noop_styled_ostream_t <b>noop_styled_ostream_create</b><i> (ostream_t <var>destination</var>, bool <var>pass_ownership</var>)</i>
	<a name="IDX50"></a>
	</dt>
	<dd><p>Creates an output stream that delegates to <code><var>destination</var></code> and
	that supports the styling operations as no-ops.
	</p>
	<p>If <code><var>pass_ownership</var></code> is <code>true</code>, closing the resulting
	stream will automatically close the <code><var>destination</var></code>.
	</p>
	<p>Note: If <code><var>pass_ownership</var></code> is <code>false</code>, the resulting stream
	must be closed before <code><var>destination</var></code> can be closed.
	</p></dd></dl>


	<a name="Debugging-the-styling-code"></a>
	<a name="SEC35"></a>
	<h2 class="section"> <a href="libtextstyle_toc.html#TOC35">3.6 Debugging the text styling support</a> </h2>

	<p>If you want to understand which output of your program is associated with
	which CSS classes, the simplest way is as follows:
	</p>
	<ol>
	<li>
	Run the program with the command-line option <code>--color=html</code>,
	redirecting the output to a file.
	</li><li>
	Then inspect this output. Text regions associated with a CSS class are
	surrounded by <code><span class="<var>css-class</var>"></code>...<code></span></code>.
	</li></ol>


	<a name="What-to-document"></a>
	<a name="SEC36"></a>
	<h2 class="section"> <a href="libtextstyle_toc.html#TOC36">3.7 Documenting the text styling support</a> </h2>

	<p>To make the text styling support available to the end user of your
	package, the following need to be documented:
	</p><ul>
	<li>
	The command-line options. This typically needs to be done in several
	places: in the ‘<samp>--help</samp>’ output, in the <code>man</code> pages (if present),
	and in the documentation.
	</li><li>
	Which programs support ‘<samp>--color=test</samp>’?
	</li><li>
	The list of CSS classes and their meaning. This is necessary, so that
	the user can create their own style file; the CSS classes are part of the
	selectors in the CSS rules.
	</li><li>
	The location of the default style file. This is a convenience, so that
	the user, when creating their own style file, can start from the default
	one.
	</li><li>
	The environment variable, called <code><var>style_file_envvar</var></code> above,
	that, when set to a non-empty value, specifies the style file to use.
	</li></ul>


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