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+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
+<html>
+<head>
+<title>Ghostscript C coding guidelines</title>
+<!-- $Id: C-style.htm,v 1.21.2.11.2.5 2003/05/17 14:38:59 giles Exp $ -->
+<!-- Originally: c-style.txt -->
+<link rel="stylesheet" type="text/css" href="gs.css" title="Ghostscript Style">
+</head>
+
+<body>
+<!-- [1.0 begin visible header] ============================================ -->
+
+<!-- [1.1 begin headline] ================================================== -->
+
+<h1>Ghostscript C coding guidelines</h1>
+
+<!-- [1.1 end headline] ==================================================== -->
+
+<!-- [1.2 begin table of contents] ========================================= -->
+
+<h2>Table of contents</h2>
+
+<blockquote><ul>
+<li><a href="#Introduction">Introduction</a>
+<li><a href="#C_language">C language do's and don'ts</a>
+<ul>
+<li>Preprocessor:
+ <a href="#Conditionals">Conditionals</a>,
+ <a href="#Macros">Macros</a>,
+ <a href="#Preprocessor_other">Other</a>
+<li><a href="#Lexical_elements">Lexical elements</a>
+<li><a href="#Scoping">Scoping</a>
+<li>Data types:
+ <a href="#Scalars">Scalars</a>,
+ <a href="#Arrays">Arrays</a>,
+ <a href="#Typedefs">Typedefs</a>,
+ <a href="#Structures">Structures</a>,
+ <a href="#Unions">Unions</a>
+<li><a href="#Expressions">Expressions</a>
+<li><a href="#Statements">Statements</a>
+<li><a href="#Procedures">Procedures</a> (prototypes and definitions)
+<li><a href="#Standard_library">Standard library</a>
+</ul>
+<li><a href="#Language_extensions">Language extensions</a>
+<li><a href="#Stylistic_conventions">Stylistic conventions</a>
+<ul>
+<li>Formatting:
+ <a href="#Indentation">Indentation</a>,
+ <a href="#Spaces">Spaces</a>,
+ <a href="#Parentheses">Parentheses</a>
+<li><a href="#Preprocessor_style">Preprocessor</a>
+<li><a href="#Naming">Naming</a>
+<li><a href="#Types">Types</a>
+<li><a href="#Procedures_style">Procedures</a>,
+<li>Miscellany:
+ <a href="#Local_variables">Local variables</a>,
+ <a href="#Compiler_warnings">Compiler warnings</a>
+</ul>
+<li><a href="#File_structuring">File structuring and naming</a>
+<ul>
+<li><a href="#All_files">All files</a>
+<li><a href="#Makefiles">Makefiles</a>
+<li><a href="#General_C_code">General C Code</a>
+<li><a href="#Headers">Headers (<b><tt>.h</tt></b> files)</a>
+<li><a href="#Source">Source (<b><tt>.c</tt></b> files)</a>
+</ul>
+<li><a href="#Conventions">Ghostscript conventions</a>
+<ul>
+<li><a href="#Specific_names">Specific names</a>:
+ <a href="#code"><b><tt>code</tt></b></a>,
+ <a href="#status"><b><tt>status</tt></b></a>
+<li><a href="#Structure_type_descriptors">Structure type descriptors</a>
+<li><a href="#Objects">"Objects"</a>
+<li><a href="#Error_handling">Error handling</a>
+</ul>
+</ul></blockquote>
+
+<!-- [1.2 end table of contents] =========================================== -->
+
+<!-- [1.3 begin hint] ====================================================== -->
+
+<p>
+For other information, see the <a href="Readme.htm">Ghostscript
+overview</a>.
+
+<!-- [1.3 end hint] ======================================================== -->
+
+<hr>
+
+<!-- [1.0 end visible header] ============================================== -->
+
+<!-- [2.0 begin contents] ================================================== -->
+
+<h2><a name="Introduction"></a>Introduction</h2>
+
+<p>
+This document describes Ghostscript's C coding conventions. It is primarily
+<em>prescriptive</em>, documenting what developers should do when writing
+new code; the companion developer documentation (<a
+ href="Develop.htm">Develop.htm</a>) is primarily <em>descriptive</em>,
+documenting the way things are.
+
+<p>
+We encourage following the general language usage and stylistic rules for
+any code that will be integrated with Ghostscript, even if the code doesn't
+use Ghostscript's run-time facilities or have anything to do with
+PostScript, PDF, or page description languages. Ghostscript itself follows
+some additional conventions; these are documented separately under "<a
+href="#Conventions">Ghostscript conventions</a>" below.
+
+<hr>
+
+<h2><a name="C_language"></a>C language do's and don'ts</h2>
+
+<p>
+There are several different versions of the C language, and even of the ANSI
+C standard. Ghostscript versions through 7.0 were designed to compile on
+pre-ANSI compilers as well as on many compilers that implemented the ANSI
+standard with varying faithfulness. Ghostscript versions since 7.0 do not
+cater for pre-ANSI compilers: they must conform to the ANSI 1989 standard
+(ANS X3.159-1989), with certain restrictions and a few conventional
+additions.
+
+<h3>Preprocessor</h3>
+
+<h4><a name="Conditionals"></a>Conditionals</h4>
+
+Restrictions:
+
+<ul>
+
+<li>Don't assume that <b><tt>#if</tt></b> will treat undefined names as 0.
+While the ANSI standard requires this, it may produce a warning.
+
+<li>In <b><tt>.c</tt></b> files, don't use preprocessor conditionals that
+test for individual platforms or compilers. Use them only in header files
+named xxx<b><tt>_.h</tt></b>.
+
+</ul>
+
+<h4><a name="Macros"></a>Macros</h4>
+
+<p>
+Restrictions:
+
+<ul>
+
+<li>Don't redefine a macro, even with the same definition, without using
+<b><tt>#undef</tt></b>.
+
+<li><b><tt>CAPITALIZE</tt></b> macro names unless there is a good reason not
+to.
+
+<li>Don't use a macro call within a macro argument if the call expands to a
+token sequence that includes any commas not within parentheses: this
+produces different results depending on whether the compiler expands the
+inner call before or after the argument is substituted into the macro body.
+(The ANSI standard says that calls must be expanded after substitution, but
+some compilers do it the other way.)
+
+<li>Don't use macro names, even inadvertently, in string constants. Some
+compilers erroneously try to expand them.
+
+<li>Don't use macros to define shorthands for casted pointers. For
+instance, avoid
+
+<blockquote><b><tt>
+#define fdev ((gx_device_fubar *)dev)
+</tt></b></blockquote>
+
+<p>
+and instead use
+
+<blockquote><b><tt>
+gx_device_fubar * const fdev = (gx_device_fubar *)dev;
+</tt></b></blockquote>
+
+<p>
+The use of <b><tt>const</tt></b> alerts the reader that this is effectively
+a synonym.
+
+<li>If a macro generates anything larger than a single expression (that is,
+one or more statements), surround it with <b><tt>BEGIN</tt></b> and
+<b><tt>END</tt></b>. These work around the fact that simple statements and
+compound statements in C can't be substituted for each other syntactically.
+
+</ul>
+
+<h3><a name="Preprocessor_other"></a>Other</h3>
+
+<p>
+Restrictions:
+
+<ul>
+
+<li>Only use <b><tt>#pragma</tt></b> in files that are explicitly identified
+as being platform-dependent. Many compilers complain if this is used at
+all, and some complain if they don't recognize the specific pragma being
+requested (both incorrect according to the ANSI standard).
+
+</ul>
+
+<h3><a name="Lexical_elements"></a>Lexical elements</h3>
+
+<p>
+Do not use:
+
+<ul>
+
+<li>ANSI trigraphs (??x)
+<li>Nested comments (/* /* */ */) (not ANSI compliant, but often accepted)
+<li>Multi-character character constants ('abc')
+<li>Wide-character character or string constants (L'x', L"x")
+
+</ul>
+
+<p>
+Restrictions:
+
+<ul>
+
+<li>Procedure and static variable names must be 31 characters or less.
+
+<li>Externally visible procedure and variable names must be unique in the
+first 23 characters.
+
+</ul>
+
+<h3><a name="Scoping"></a>Scoping (extern, static, ...)</h3>
+
+<p>
+Do not use:
+
+<ul>
+
+<li><b><tt>register</tt></b>
+
+</ul>
+
+<p>
+Restrictions:
+
+<ul>
+
+<li>Do not allow a global variable (constant) to have more than one
+non-<b><tt>extern</tt></b> definition, even though some ANSI C compilers
+allow this. Every global constant should have exactly one definition, in a
+<b><tt>.c</tt></b> file, and preferably just one <b><tt>extern</tt></b>
+declaration, in a header file.
+
+<li>Use <b><tt>private</tt></b> instead of <b><tt>static</tt></b> for
+procedures and variables declared at the outermost scope of a file. This
+allows making such constructs either visible or invisible to profilers by
+changing a single <b><tt>#define</tt></b>.
+
+<li><b><tt>static</tt></b> or <b><tt>private</tt></b> variables must be
+<b><tt>const</tt></b> and initialized: non-<b><tt>const</tt></b> statically
+allocated variables are incompatible with reentrancy, and we're in the
+process of eliminating all of them.
+
+<li>Do not use <b><tt>extern</tt></b> in <b><tt>.c</tt></b> files, only in
+<b><tt>.h</tt></b> files, unless you have a very good reason for it (e.g.,
+as in <a href="../src/iconf.c">iconf.c</a>). There are too many such
+<b><tt>extern</tt></b>s in the code now: we are eliminating them over time.
+
+<li>Do not declare the same name as both <b><tt>static</tt></b>
+(<b><tt>private</tt></b>) and non-<b><tt>static</tt></b> within the same
+compilation. (Some compilers complain, some do not.) This is especially a
+problem for procedures: it is easy to declare a procedure as
+<b><tt>private</tt></b> near the beginning of a file and accidentally not
+declare it <b><tt>private</tt></b> where it is defined later in the file.
+
+<li>Even though the ANSI standard allows initialized external declarations
+(<b><tt>extern&nbsp;int&nbsp;x&nbsp;=&nbsp;0</tt></b>), don't use them.
+
+</ul>
+
+<h3><a name="Scalars"></a>Scalars</h3>
+
+<p>
+Restrictions:
+
+<ul>
+
+<li>Avoid using <b><tt>char</tt></b>, except for <b><tt>char&nbsp;*</tt></b>
+for a pointer to a string. Don't assume that <b><tt>char</tt></b> is
+signed; also don't assume it is unsigned.
+
+<li>Never cast a <b><tt>float</tt></b> to a <b><tt>double</tt></b>
+explicitly. ANSI compilers in their default mode do all floating point
+computations in double precision, and handle such casts automatically.
+
+<li>Don't use <b><tt>long long</tt></b>: even though it is in the ANSI
+standard, not all compilers support it. Use <b><tt>bits64</tt></b> instead
+(see below under "<a href="#Language_extensions">Language extensions</a>").
+
+<li>Don't assume anything about whether <b><tt>sizeof(long)</tt></b> is less
+than, equal to, or greater than <b><tt>sizeof(ptr)</tt></b>. (However, you
+can make such comparisons in preprocessor conditionals using
+<b><tt>ARCH_SIZEOF_LONG</tt></b> and <b><tt>ARCH_SIZEOF_PTR</tt></b>.)
+
+</ul>
+
+<h3><a name="Arrays"></a>Arrays</h3>
+
+<p>
+Restrictions:
+
+<ul>
+
+<li>Don't declare arrays of size 0. (The newer ANSI standard allows this,
+but the older one doesn't.)
+
+<li>Don't declare an array of size 1 at the end of a structure to indicate
+that a variable-size array follows.
+
+<li>Don't declare initialized <b><tt>auto</tt></b> arrays.
+
+</ul>
+
+<h3><a name="Typedefs"></a>Typedefs</h3>
+
+<p>
+Restrictions:
+
+<ul>
+
+<li>Don't use <b><tt>typedef</tt></b> for function types, such as
+
+<blockquote>
+<b><tt>typedef int proc_xyz_t(double, int *);</tt></b>
+</blockquote>
+
+<p>Many compilers don't handle this correctly -- they will give errors, or
+do the wrong thing, when declaring variables of type
+<b><tt>proc_xyz_t</tt></b> and/or <b><tt>proc_xyz_t *</tt></b>. Instead, do
+this:
+
+<blockquote>
+<b><tt>#define PROC_XYZ(proc) int proc(double, int *)<br>
+PROC_XYZ(some_proc); /* declare a procedure of this type */<br>
+typedef PROC_XYZ((*proc_xyz_ptr_t)); /* define a type for procedure ptrs */<br>
+<br>
+proc_xyz_ptr_t pp; /* pointer to procedure */</tt></b>
+</blockquote>
+
+<li>Don't redefine <b><tt>typedef</tt></b>'ed names, even with the same
+definition. Some compilers complain about this, and the standard doesn't
+allow it.
+
+</ul>
+
+<h3><a name="Structures"></a>Structures</h3>
+
+<p>
+Restrictions:
+
+<li>Don't use anonymous structures if you can possibly avoid it, except
+occasionally as components of other structures. Ideally, use the
+<b><tt>struct</tt></b> keyword only for declaring named structure types,
+like this:
+
+<blockquote>
+<b><tt>typedef struct xxx_s {</tt></b><br>
+&nbsp;&nbsp;&nbsp;... members ...<br>
+<b><tt>} xxx_t;</tt></b>
+</blockquote>
+
+<li>Use <b><tt>struct</tt></b> only when declaring structure types, never
+for referring to them (e.g., never declare a variable as type
+<b><tt>struct&nbsp;xxx_s&nbsp;*</tt></b>).
+
+<li>Don't assume that the compiler will (or won't) insert padding in
+structures to align members for best performance. To preserve alignment,
+only declare structure members that are narrower than an <b><tt>int</tt></b>
+if there will be a lot of instances of that structure in memory. For such
+structures, insert <b><tt>byte</tt></b> and/or <b><tt>short</tt></b> padding
+members as necessary to re-establish <b><tt>int</tt></b> alignment.
+
+<li>Don't declare initialized <b><tt>auto</tt></b> structures.
+
+</ul>
+
+<h3><a name="Unions"></a>Unions</h3>
+
+<p>
+Restrictions:
+
+<ul>
+
+<li>Use unions only as components of structures, not as typedefs in their
+own right.
+
+<li>Don't attempt to initialize unions: not all compilers support this, even
+though it is in the 1989 ANSI standard.
+
+</ul>
+
+<h3><a name="Expressions"></a>Expressions</h3>
+
+<p>
+Restrictions:
+
+<ul>
+
+<li>Don't assign a larger integer data type to a smaller one without a cast
+(<b><tt>int_x&nbsp;=&nbsp;long_y</tt></b>).
+
+<li>It's OK to use the address of a structure or array element
+(<b><tt>&p->e</tt></b>, <b><tt>&a[i]</tt></b>) locally, or pass it to a
+procedure that won't store it, but don't store such an address in allocated
+storage unless you're very sure of what you're doing.
+
+<li>Don't use conditional expressions with structure or union values.
+(Pointers to structures or unions are OK.)
+
+<li>For calling a variable or parameter procedure, use
+<b><tt>ptr-&gt;func(...)</tt></b>. Some old code uses explicit indirection,
+<b><tt>(*ptr-&gt;func)(...)</tt></b>: don't use this in new code.
+
+<li>Don't write expressions that depend on order of evaluation, unless the
+order is created explicitly by use of <b><tt>||</tt></b>,
+<b><tt>&amp;&amp;</tt></b>, <b><tt>?:</tt></b>, <b><tt>,</tt></b>, or
+function nesting (the arguments of a function must be evaluated before the
+function is called). In particular, don't assume that the arguments of a
+function will be evaluated left-to-right, or that the left side of an
+assignment will be evaluated before the right.
+
+<li>Don't mix integer and enumerated types ad lib: treat enumerated types as
+distinct from integer types, and use casts to convert between the two.
+(Some compilers generate warnings if you do not do this.)
+
+</ul>
+
+<h3><a name="Statements"></a>Statements</h3>
+
+<p>
+Restrictions:
+
+<ul>
+
+<li>If you use an expression as a statement, other than an assignment or a
+function call with <b><tt>void</tt></b> return value, enclose it explicitly
+in <b><tt>DISCARD()</tt></b>.
+
+<li>The type of the operand of a <b><tt>switch</tt></b> must match the type
+of the case labels, whether the labels are <b><tt>int</tt></b>s or the
+members of an <b><tt>enum</tt></b> type. (Use a cast if necessary.)
+
+<li>It is OK for one case of a switch to "fall through" into another (i.e.,
+for the statement just before a case label not to be a control transfer),
+but a comment <b><tt>/*&nbsp;falls&nbsp;through&nbsp;*/</tt></b> is
+required.
+
+<li>If you are returning an error code specified explicitly (e.g.,
+<b><tt>return&nbsp;gs_error_rangecheck</tt></b> or
+<b><tt>return&nbsp;e_rangecheck</tt></b>), use
+<b><tt>return_error()</tt></b> rather than plain <b><tt>return</tt></b>.
+However, if the program is simply propagating an error code generated
+elsewhere, as opposed to generating the error, use <b><tt>return</tt></b>
+(e.g., <b><tt>if&nbsp;(code&nbsp;<&nbsp;0)&nbsp;return&nbsp;code</tt></b>).
+
+</ul>
+
+<h3><a name="Procedures"></a>Procedures</h3>
+
+<p>
+Restrictions:
+
+<ul>
+
+<li>Provide a prototype for every procedure, and make sure the prototype is
+available at every call site. If the procedure is local to a file
+(<b><tt>private</tt></b>), the prototype should precede the procedure, in
+the same file; if the procedure is global, the prototype should be in a
+header file.
+
+<li>If a procedure parameter is itself a procedure, do list its parameter
+types rather than just using <b><tt>()</tt></b>. For example,
+
+<blockquote><b><tt>
+int foo(int (*callback)(int, int));
+</tt></b></blockquote>
+
+<p>
+rather than just
+
+<blockquote><b><tt>
+int foo(int (*callback)());
+</tt></b></blockquote>
+
+<li>Don't use the <b><tt>P</tt></b>* macros in new code. (See the
+Procedures section of <a href="#Language_extensions">Language extensions</a>
+below for more information.)
+
+<li>Always provide an explicit return type for procedures, in both the
+prototype and the definition: don't rely on the implicit declaration as
+<b><tt>int</tt></b>.
+
+<li>Don't use <b><tt>float</tt></b> as the return type of a procedure,
+unless there's a special reason. Floating point hardware typically does
+everything in double precision internally and has to do extra work to
+convert between double and single precision.
+
+<li>Don't declare parameters as being of type <b><tt>float</tt></b>,
+<b><tt>short</tt></b>, or <b><tt>char</tt></b>. If you do this and forget
+to include the prototype at a call site, ANSI compilers will generate
+incompatible calling sequences. Use <b><tt>floatp</tt></b> (a synonym for
+<b><tt>double</tt></b>, mnemonic for "float parameter") instead of
+<b><tt>float</tt></b>, and use <b><tt>int</tt></b> or <b><tt>uint</tt></b>
+instead of <b><tt>short</tt></b> or <b><tt>char</tt></b>.
+
+</ul>
+
+<h3><a name="Standard_library"></a>Standard library</h3>
+
+<p>
+Restrictions:
+
+<ul>
+
+<li>Only use library features that are documented in the established ANSI
+standard (e.g., Harbison & Steele's book). Do not use procedures that are
+"standards" promulgated by Microsoft (e.g., <b><tt>stricmp</tt></b>), or
+originate in BSD Unix (e.g., <b><tt>strcasecmp</tt></b>), or were added in
+later versions of the standard such as C 9X.
+
+<li>Do not use any features from <b><tt>stdio.h</tt></b> that assume the
+existence of <b><tt>stdin</tt></b>, <b><tt>stdout</tt></b>, or
+<b><tt>stderr</tt></b>. See <a href="../src/gsio.h">gsio.h</a> for the full
+list. Instead, use <b><tt>gs_stdin</tt></b> et al.
+
+</ul>
+
+<hr>
+
+<h2><a name="Language_extensions"></a>Language extensions</h2>
+
+<h3>Scoping</h3>
+
+<dl>
+
+<dt><b><tt>inline</tt></b>
+
+<dd><b><tt>inline</tt></b> is available even if the compiler does not
+support it. Be aware, however, that it may have no effect. In particular,
+do not use <b><tt>inline</tt></b> in header files. Instead, use the
+<b><tt>extern_inline</tt></b> facility described just below.
+
+<dt><b><tt>extern_inline</tt></b>
+
+<dd>Compilers that do support <b><tt>inline</tt></b> vary in how they decide
+whether to (also) compile a closed-code copy of the procedure. Because of
+this, putting an <b><tt>inline</tt></b> procedure in a header file may
+produce multiple closed copies, causing duplicate name errors at link time.
+<b><tt>extern_inline</tt></b> provides a safe way to put
+<b><tt>inline</tt></b> procedures in header files, regardless of compiler.
+Unfortunately, the only way we've found to make this fully portable involves
+a fair amount of boilerplate. For details, please see <a
+href="../src/stdpre.h">stdpre.h</a>.
+
+<dt><b><tt>private</tt></b>
+
+<dd><b>Use <tt>private</tt></b> instead of <b><tt>static</tt></b> for all
+file-local procedures, and also for file-local variables defined at the
+outermost level. However, use <b><tt>static</tt></b>, not
+<b><tt>private</tt></b>, for variables defined within a procedure.
+
+<p>
+<b><tt>private</tt></b> is normally #define'd as <b><tt>static</tt></b>.
+However, it can also be #define'd as empty, which allows profilers to
+measure all procedures, and 'nm' to list all interesting statically
+allocated variables, not just public ones.
+
+</dl>
+
+<h3>Scalar types</h3>
+
+<dl>
+
+<dt><b><tt>bool, true, false</tt></b>
+
+<dd><b><tt>bool</tt></b> is intended as a Boolean type, with canonical
+values <b><tt>true</tt></b> and <b><tt>false</tt></b>. In a more reasonable
+language, such as Java, <b><tt>bool</tt></b> is an enumerated type requiring
+an explicit cast to or from <b><tt>int</tt></b>; however, because C's
+conditionals are defined as producing <b><tt>int</tt></b> values, we can't
+even define <b><tt>bool</tt></b> as a C <b><tt>enum</tt></b> without
+provoking compiler warnings.
+
+<p>
+Even though <b><tt>bool</tt></b> is a synonym for <b><tt>int</tt></b>, treat
+them as conceptually different types:
+
+<ul>
+<li>Initialize or set <b><tt>bool</tt></b> variables to <b><tt>true</tt></b>
+or <b><tt>false</tt></b>, not 0 or 1.
+<li>Use the Boolean operators <b><tt>!</tt></b>, <b><tt>&&</tt></b>,
+and <b><tt>||</tt></b> only with Booleans. Don't use the idiom
+<b><tt>!!x</tt></b> to create a Boolean that is true iff <b><tt>x</tt></b>
+!= 0: use <b><tt>x != 0</tt></b>.
+<li>Use an explicit <b><tt>(int)</tt></b> cast to convert a Boolean to an
+integer.
+</ul>
+
+<dt><b><tt>byte, ushort, uint, ulong</tt></b>
+
+<dd>These types are simply shorthands for <b><tt>unsigned char, short, int,
+long</tt></b>.
+
+<dt><b><tt>floatp</tt></b>
+
+<dd>This is a synonym for <b><tt>double</tt></b>. It should be used for,
+and only for, procedure parameters that would otherwise be
+<b><tt>float</tt></b>. (As noted above, procedure parameters should not be
+declared as <b><tt>float</tt></b>.)
+
+<dt><b><tt>bits8, bits16, bits32</tt></b>
+
+<dd>These are unsigned integer types of the given width. Use them wherever
+the actual width matters: do <em>not</em>, for example, use
+<b><tt>short</tt></b> assuming that it is 16 bits wide.
+
+<dt><b><tt>bits64</tt></b>
+
+<dd><strong>****** NOT IMPLEMENTED YET ******</strong>
+This is an unsigned 64-bit integer type, but it may not be available on all
+platforms. Any code that uses this type should be surrounded by
+<b><tt>#if&nbsp;ARCH_HAS_BITS64</tt></b>.
+
+</dl>
+
+<h3>Procedures</h3>
+
+<dl>
+
+<dt><b><tt>P0(), P1(p1), ..., P16(p1, ..., p16)</tt></b> [deprecated]
+
+<dd>Nearly all existing code uses these macros for the parameter lists of
+procedure prototypes, e.g.,
+<b><tt>int&nbsp;proc(P2(int&nbsp;a,&nbsp;int&nbsp;b))</tt></b>, to provide
+compatibility with pre-ANSI, a.k.a. "traditional" or "K &amp; R", compilers.
+Since only ANSI compilers are now supported, don't use these macros in new
+code: use the ANSI standard syntax
+<b><tt>int&nbsp;proc(int&nbsp;a,&nbsp;int&nbsp;b)</tt></b>.
+
+</dl>
+
+<hr>
+
+<h2><a name="Stylistic_conventions"></a>Stylistic conventions</h2>
+
+<p>
+Ghostscript's coding rules cover not only the use of the language, but also
+many stylistic issues like the choice of names and the use of whitespace.
+The stylistic rules are meant to produce code that is easy to read. It's
+important to observe them as much as possible in order to maintain a
+consistent style, but if you find these rules getting in your way or
+producing ugly-looking results once in a while, it's OK to break it.
+
+<h3><a name="Formatting"></a>Formatting</h3>
+
+<h4><a name="Indentation"></a>Indentation</h4>
+
+<p>
+We've formatted all of our code using the GNU <b><tt>indent</tt></b> program.
+
+<blockquote><b><tt>
+indent&nbsp;-bad&nbsp;-nbap&nbsp;-nsob&nbsp;-br&nbsp;-ce&nbsp;-cli4&nbsp;-npcs&nbsp;-ncs&nbsp;\<br>
+&nbsp;&nbsp;&nbsp;-i4&nbsp;-di0&nbsp;-psl&nbsp;-lp&nbsp;-lps&nbsp;somefile.c
+</tt></b></blockquote>
+
+<p>
+does a 98% accurate job of producing our preferred style. Unfortunately,
+there are bugs in all versions of GNU <b><tt>indent</tt></b>, requiring
+both pre- and post-processing of the code. The <b><tt>gsindent</tt></b>
+script in the Ghostscript fileset contains the necessary workarounds.
+
+<p>
+Put indentation points every 4 spaces, with 8 spaces = 1 tab stop.
+
+<p>
+For assignments (including chain assignments), put the entire statement on
+one line if it will fit; if not, break it after a <b><tt>=</tt></b> and
+indent all the following lines. I.e., format like this:
+
+<blockquote>
+var1&nbsp;<b><tt>=</tt></b>&nbsp;value<b><tt>;</tt></b><br>
+var1&nbsp;<b><tt>=</tt></b>&nbsp;var2&nbsp;<b><tt>=</tt></b>&nbsp;value<b><tt>;</tt></b><br>
+var1&nbsp;<b><tt>=</tt></b><br>
+&nbsp;&nbsp;&nbsp;&nbsp;value<b><tt>;</tt></b><br>
+var1&nbsp;<b><tt>=</tt></b><br>
+&nbsp;&nbsp;&nbsp;&nbsp;var2&nbsp;<b><tt>=</tt></b>&nbsp;value<b><tt>;</tt></b><br>
+var1&nbsp;<b><tt>=</tt></b>&nbsp;var2&nbsp;<b><tt>=</tt></b><br>
+&nbsp;&nbsp;&nbsp;&nbsp;value<b><tt>;</tt></b>
+</blockquote>
+
+<p>
+But not like this:
+
+<blockquote>
+var1&nbsp;<b><tt>=</tt></b><br>
+var2&nbsp;<b><tt>=</tt></b> value<b><tt>;</tt></b>
+</blockquote>
+
+<p>
+Indent in-line blocks thus:
+
+<blockquote>
+<b><tt>{</tt></b><br>
+&nbsp;&nbsp;&nbsp;... declarations ...<br>
+&nbsp;&nbsp;&nbsp;{{ blank line if any declarations above }}<br>
+&nbsp;&nbsp;&nbsp;... statements ...<br>
+<b><tt>}</tt></b>
+</blockquote>
+
+<p>
+Similarly, indent procedures thus:
+
+<blockquote>
+return_type<br>
+proc_name(... arguments ...)<br>
+<b><tt>{</tt></b><br>
+&nbsp;&nbsp;&nbsp;... declarations ...<br>
+&nbsp;&nbsp;&nbsp;{{ blank line if any declarations above }}<br>
+&nbsp;&nbsp;&nbsp;... statements ...<br>
+<b><tt>}</tt></b>
+</blockquote>
+
+<p>
+If a control construct (<b><tt>if</tt></b>, <b><tt>do</tt></b>,
+<b><tt>while</tt></b>, or <b><tt>for</tt></b>) has a one-line body, use
+this:
+
+<blockquote>
+... control construct ...<br>
+&nbsp;&nbsp;&nbsp;... subordinate simple statement ...
+</blockquote>
+
+<p>
+If it has a multi-line body, use this:
+
+<blockquote>
+... control construct ... <b><tt>{</tt></b><br>
+&nbsp;&nbsp;&nbsp;... subordinate code ...<br>
+<b><tt>}</tt></b>
+</blockquote>
+
+<p>
+If the subordinate code has declarations, see blocks above.
+
+<p>
+For if-else statements, do this:
+
+<blockquote>
+<b><tt>if (</tt></b> ...<b><tt> ) {</tt></b><br>
+&nbsp;&nbsp;&nbsp;... subordinate code ...<br>
+<b><tt>} else if (</tt></b> ...<b><tt> ) {</tt></b><br>
+&nbsp;&nbsp;&nbsp;... subordinate code ...<br>
+<b><tt>} else {</tt></b><br>
+&nbsp;&nbsp;&nbsp;... subordinate code ...<br>
+<b><tt>}</tt></b>
+</blockquote>
+
+<p>
+When there are more than two alternatives, as in the example above, use the
+above ("parallel") syntax rather than the following ("nested") syntax:
+
+<blockquote>
+<b><tt>if (</tt></b> ...<b><tt> ) {</tt></b><br>
+&nbsp;&nbsp;&nbsp;... subordinate code ...<br>
+<b><tt>} else {</tt></b><br>
+<b><tt>&nbsp;&nbsp;&nbsp;if (</tt></b> ...<b><tt> ) {</tt></b><br>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;... subordinate code ...<br>
+<b><tt>&nbsp;&nbsp;&nbsp;} else {</tt></b><br>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;... subordinate code ...<br>
+<b><tt>&nbsp;&nbsp;&nbsp;}</tt></b><br>
+<b><tt>}</tt></b>
+</blockquote>
+
+<p>
+Similarly, for do-while statements, do this:
+
+<blockquote>
+<b><tt>do {</tt></b><br>
+&nbsp;&nbsp;&nbsp;... body ...<br>
+<b><tt>} while (</tt></b> ... condition ... <b><tt>);</tt></b>
+</blockquote>
+
+<h4><a name="Spaces"></a>Spaces</h4>
+
+<p>
+Do put a space:
+<ul>
+<li>after every comma and semicolon, unless it ends a line;
+<li>around every binary operator other than "<b><tt>-&gt;</tt></b>" and
+"<b><tt>.</tt></b>", although you can omit the spaces around the innermost
+operator in a nested expression if you like;
+<li>on both sides of the parentheses of an <b><tt>if</tt></b>, <b><tt>for</tt></b>, or <b><tt>while</tt></b>.
+</ul>
+
+<p>
+Don't put a space:
+<ul>
+<li>at the end of a line;
+<li>before a comma or semicolon;
+<li>after unary prefix operators;
+<li>before the parenthesis of a macro or procedure call.
+</ul>
+
+<h4><a name="Parentheses"></a>Parentheses</h4>
+
+<p>
+Parentheses are important in only a few places:
+
+<ul>
+<li>Around the inner subexpressions in expressions that mix
+<b><tt>&amp;&amp;</tt></b> and <b><tt>||</tt></b>, even if they are not
+required by precedence, for example
+
+<blockquote><b><tt>
+(xx &amp;&amp; yy) || zz
+</tt></b></blockquote>
+
+<li>Similarly around inner subexpressions in expressions that mix
+<b><tt>&amp;</tt></b>, <b><tt>|</tt></b>, or shifts, especially if mixing
+these with other operators, for instance
+
+<blockquote><b><tt>
+(x &lt;&lt; 3) | (y &gt;&gt; 5)
+</tt></b></blockquote>
+
+<li>In macro definitions around every use of an argument that logically
+could be an expression, for example
+
+<blockquote><b><tt>
+((x) * (x) + (y) * (y))
+</tt></b></blockquote>
+
+</ul>
+
+<p>
+Anywhere else, given the choice, use fewer parentheses.
+
+<p>
+For stylistic consistency with the existing Ghostscript code, put
+parentheses around conditional expressions even if they aren't
+syntactically required, unless you really dislike doing this. Note that
+the parentheses should go around the entire expression, not the condition.
+For instance, instead of
+
+<blockquote><b><tt>
+hpgl_add_point_to_path(pgls, arccoord_x, arccoord_y,<br>
+&nbsp;&nbsp;&nbsp;(pgls-&gt;g.pen_down) ? gs_lineto : gs_moveto);
+</tt></b></blockquote>
+
+<p>
+use
+
+<blockquote><b><tt>
+hpgl_add_point_to_path(pgls, arccoord_x, arccoord_y,<br>
+&nbsp;&nbsp;&nbsp;(pgls-&gt;g.pen_down ? gs_lineto : gs_moveto));
+</tt></b></blockquote>
+
+<h3><a name="Preprocessor_style"></a>Preprocessor</h3>
+
+<h4>Conditionals</h4>
+
+<p>
+Using preprocessor conditionals can easily lead to unreadable code, since
+the eye really wants to read linearly rather than having to parse the
+conditionals just to figure out what code is relevant. It's OK to use
+conditionals that have small scope and that don't change the structure or
+logic of the program (typically, they select between different sets of
+values depending on some configuration parameter), but where possible, break
+up source modules rather than use conditionals that affect the structure or
+logic.
+
+<h4>Macros</h4>
+
+<p>
+Ghostscript code uses macros heavily to effectively extend the rather
+weak abstraction capabilities of the C language, specifically in the area of
+memory management and garbage collection: in order to read Ghostscript code
+effectively, you simply have to learn some of these macros as though they
+were part of the language. The current code also uses macros heavily for
+other purposes, but we are trying to phase these out as rapidly as possible,
+because they make the code harder to read and debug, and to use the
+rules that follow consistently in new code.
+
+<p>
+Define macros in the smallest scope you can manage (procedure, file, or
+<b><tt>.h</tt></b> file), and <b><tt>#undef</tt></b> them at the end of
+that scope: that way, someone reading the code can see the definitions
+easily when reading the uses. If that isn't appropriate, define them in as
+large a scope as possible, so that they effectively become part of the
+language. This places an additional burden on the reader, but it can be
+amortized over reading larger amounts of code.
+
+<p>
+Try hard to use procedures instead of macros. Use "<b><tt>inline</tt></b>"
+if you really think the extra speed is needed, but only within a
+<b><tt>.c</tt></b> file: don't put inline procedures in <b><tt>.h</tt></b>
+files, because most compilers don't honor "<b><tt>inline</tt></b>" and
+you'll wind up with a copy of the procedure in every <b><tt>.c</tt></b>
+file that includes the <b><tt>.h</tt></b> file.
+
+<p>
+If you define a macro that looks like a procedure, make sure it will work
+wherever a procedure will work. In particular, put parentheses around every
+use of an argument within the macro body, so that the macro will parse
+correctly if some of the arguments are expressions, and put parentheses
+around the entire macro body. (This is still subject to the problem that an
+argument may be evaluated more than once, but there is no way around this in
+C, since C doesn't provide for local variables within expressions.)
+
+<p>
+If you define macros for special loop control structures, make their uses
+look somewhat like ordinary loops, for instance:
+
+<blockquote>
+<b><tt>BEGIN_RECT(xx, yy) {</tt></b><br>
+&nbsp;&nbsp;... body indented one position ...<br>
+<b><tt>} END_RECT(xx, yy);</tt></b>
+</blockquote>
+
+<p>
+If at all possible, don't use free variables in macros -- that is, variables
+that aren't apparent as arguments of the macro. If you must use free
+variables, list them all in a comment at the point where the macro is
+defined.
+
+<h3><a name="Comments"></a>Comments</h3>
+
+<p>
+The most important descriptive comments are ones in header files that
+describe structures, including invariants; but every procedure or structure
+declaration, or group of other declarations, should have a comment. Don't
+spend a lot of time commenting executable code unless something unusual or
+subtle is going on.
+
+<h3><a name="Naming"></a>Naming</h3>
+
+<p>
+Use fully spelled-out English words in names, rather than contractions.
+This is most important for procedure and macro names, global variables and
+constants, values of <b><tt>#define</tt></b> and <b><tt>enum</tt></b>,
+<b><tt>struct</tt></b> and other <b><tt>typedef</tt></b> names, and
+structure member names, and for argument and variable names which have
+uninformative types like <b><tt>int</tt></b>. It's not very important for
+arguments or local variables of distinctive types, or for local index or
+count variables.
+
+<p>
+Avoid names that run English words together:
+"<b><tt>hpgl_compute_arc_center</tt></b>" is better than
+"<b><tt>hpgl_compute_arccenter</tt></b>". However, for terms drawn from
+some predefined source, like the names of PostScript operators, use a term
+in its well-known form (for instance, <b><tt>gs_setlinewidth</tt></b>
+rather than <b><tt>gs_set_line_width</tt></b>).
+
+<p>
+Procedures, variables, and structures visible outside a single
+<b><tt>.c</tt></b> file should generally have prefixes that indicate what
+subsystem they belong to (in the case of Ghostscript, <b><tt>gs_</tt></b>
+or <b><tt>gx_</tt></b>). This rule isn't followed very consistently.
+
+<h3><a name="Types"></a>Types</h3>
+
+<p>
+Many older structure names don't have <b><tt>_t</tt></b> on the end, but
+this suffix should be used in all new code. (The <b><tt>_s</tt></b>
+structure name is needed only to satisfy some debuggers. No code other than
+the structure declaration should refer to it.)
+
+<p>
+Declare structure types that contain pointers to other instances of
+themselves like this:
+
+<blockquote>
+<b><tt>typedef struct xxx_s xxx_t;</tt></b><br>
+<b><tt>struct xxx_s {</tt></b><br>
+&nbsp;&nbsp;&nbsp;... members ...<br>
+&nbsp;&nbsp;&nbsp;<b><tt>xxx_t *</tt></b>ptr_member_name;<br>
+&nbsp;&nbsp;&nbsp;... members ...<br>
+<b><tt>};</tt></b>
+</blockquote>
+
+<p>
+If, to maintain data abstraction and avoid including otherwise unnecessary
+header files, you find that you want the type <b><tt>xxx_t</tt></b> to be
+available in a header file that doesn't include the definition of the
+structure <b><tt>xxx_s</tt></b>, use this approach:
+
+<blockquote>
+<b><tt>#ifndef xxx_DEFINED</tt></b><br>
+<b><tt>#&nbsp;&nbsp;define xxx_DEFINED</tt></b><br>
+<b><tt>typedef struct xxx_s xxx_t;</tt></b><br>
+<b><tt>#endif</tt></b><br>
+<b><tt>struct xxx_s {</tt></b><br>
+&nbsp;&nbsp;&nbsp;... members ...<br>
+<b><tt>};</tt></b>
+</blockquote>
+
+<p>
+You can then copy the first 4 lines in other header files. (Don't ever
+include them in an executable code file.)
+
+<p>
+Don't bother using <b><tt>const</tt></b> for anything other than with
+pointers as described below. However, in those places where it is necessary
+to cast a pointer of type <b><tt>const&nbsp;T&nbsp;*</tt></b> to type
+<b><tt>T&nbsp;*</tt></b>, always include a comment that explains why you are
+"breaking const".
+
+<h4>Pointers</h4>
+
+<p>
+Use <b><tt>const</tt></b> for pointer referents (that is,
+<b><tt>const&nbsp;T&nbsp;*</tt></b>) wherever possible and appropriate.
+
+<p>
+If you find yourself wanting to use <b><tt>void&nbsp;*</tt></b>, try to
+find an alternative using unions or (in the case of super- and subclasses)
+casts, unless you're writing something like a memory manager that really
+treats memory as opaque.
+
+<h3><a name="Procedures_style"></a>Procedures</h3>
+
+<p>
+In general, don't create procedures that are private and only called from
+one place. However, if a compound statement (especially an arm of a
+conditional) is too long for the eye easily to match its enclosing braces
+"<b><tt>{...}</tt></b>" -- that is, longer than 10 or 15 lines -- and it
+doesn't use or set a lot of state held in outer local variables, it may be
+more readable if you put it in a procedure.
+
+<h3>Miscellany</h3>
+
+<h4><a name="Local_variables"></a>Local variables</h4>
+
+<p>
+Don't assign new values to procedure parameters. It makes debugging very
+confusing when the parameter values printed for a procedure are not the
+ones actually supplied by the caller. Instead use a separate local
+variable initialized to the value of the parameter.
+
+<p>
+If a local variable is only assigned a value once, assign it that value at
+its declaration, if possible. For example,
+
+<blockquote>
+<b><tt>int x = </tt></b>some expression <b><tt>;</tt></b>
+</blockquote>
+
+<p>
+rather than
+
+<blockquote>
+<b><tt>int x;</tt></b><br>
+...<br>
+<b><tt>x = </tt></b> some expression <b><tt>;</tt></b>
+</blockquote>
+
+<p>
+Use a local pointer variable like this to "narrow" pointer types:
+
+<blockquote>
+<b><tt>int</tt></b><br>
+someproc(... <b><tt>gx_device *dev</tt></b> ...)<br>
+<b><tt>{<br>
+&nbsp;&nbsp;&nbsp;gx_device_printer *const pdev = (gx_device_printer *)dev;</tt></b><br>
+&nbsp;&nbsp;&nbsp;...<br>
+<b><tt>}</tt></b>
+</blockquote>
+
+<h4><a name="Compiler_warnings"></a>Compiler warnings</h4>
+
+<p>
+The following section refers to the warnings produced by <b><tt>gcc</tt></b>:
+your compiler may produce different ones.
+
+<p>
+It's OK if compilation produces the following warnings:
+
+<ul>
+<li><b><tt>&lt;name&gt; might be used uninitialized in this function</tt></b>
+<li><b><tt>cast discards `const' from pointer target type</tt></b>
+</ul>
+
+<p>
+The first of these often occurs because the compiler isn't aware of control
+flow restrictions that guarantee the variable will be initialized before
+use: if it occurs in new code, check the code carefully, but don't worry
+about the message. The second is often unavoidable in code that initializes
+or frees a structure that is otherwise <b><tt>const</tt></b> during its
+lifetime.
+<p>
+
+Do work hard to eliminate all warnings other than these,
+since they often indicate the possible presence of coding errors.
+In particular, get rid of warnings about parameter passing or
+initialization that discards <b><tt>const</tt></b>,
+by using explicit casts.
+
+<hr>
+
+<h2><a name="File_structuring"></a>File structuring</h2>
+
+<h3><a name="All_files"></a>All files</h3>
+
+<p>
+Keep file names within the "8.3" format for portability:
+<ul>
+<li>Use only letters, digits, dash, and underscore in file names.
+<li>Don't assume upper and lower case letters are distinct.
+<li>Put no more than 8 characters before the ".", if any.
+<li>If there is a ".", put between 1 and 3 characters after the ".".
+</ul>
+
+<p>
+For files other than documentation files, use only lower case letters
+in the names; for HTML documentation files, capitalize the first letter.
+
+<p>
+Every code file should start with comments containing
+
+<ol>
+<li>a copyright notice,
+<li>the name of the file in the form of an RCS Id:
+
+<blockquote><b><tt>
+/*Id$: filename.ext $*/
+</tt></b></blockquote>
+
+<p>
+(using the comment convention appropriate to the language of the file), and
+
+<li>a summary, no more than one line, of what the file contains.
+</ol>
+
+<p>
+If you create a file by copying the beginning of another file, be sure to
+update the copyright year and change the file name.
+
+<h3><a name="Makefiles"></a>Makefiles</h3>
+
+<p>
+Use the extension <b><tt>.mak</tt></b> for makefiles.
+
+<p>
+For each
+
+<blockquote><b><tt>
+#include "xxx.h"
+</tt></b></blockquote>
+
+<p>
+make sure there is a dependency on <b><tt>$(xxx_h)</tt></b> in the
+makefile. If xxx ends with a "<b><tt>_</tt></b>", this rule still holds,
+so that if you code
+
+<blockquote><b><tt>
+#include "math_.h"
+</tt></b></blockquote>
+
+<p>
+the makefile must contain a dependency on "<b><tt>$(math__h)</tt></b>"
+(note the two underscores "<b><tt>__</tt></b>").
+
+<p>
+List the dependencies bottom-to-top, like the <b><tt>#include</tt></b>
+statements themselves; within each level, list them alphabetically. Do
+this also with <b><tt>#include</tt></b> statements themselves whenever
+possible (but sometimes there are inter-header dependencies that require
+bending this rule).
+
+<p>
+For compatibility with the build utilities on OpenVMS, always put a space
+before the colon that separates the target(s) of a rule from the dependents.
+
+<h3><a name="General_C_code"></a>General C code</h3>
+
+<p>
+List <b><tt>#include</tt></b> statements from "bottom" to "top", that is,
+in the following order:
+
+<blockquote><ol>
+<li>System includes (<b><tt>"xxx_.h"</tt></b>)
+<li><b><tt>gs*.h</tt></b>
+<li><b><tt>gx*.h</tt></b> (yes, <b><tt>gs</tt></b> and <b><tt>gx</tt></b>
+are in the wrong order.)
+<li><b><tt>s*.h</tt></b>
+<li><b><tt>i*.h</tt></b> (or other interpreter headers that don't start
+with "<b><tt>i</tt></b>")
+</ol></blockquote>
+
+<h3><a name="Headers"></a>Headers (<b><tt>.h</tt></b> files)</h3>
+
+<p>
+In header files, always use the following at the beginning of a header file
+to prevent double inclusion:
+
+<blockquote>
+{{ Copyright notice etc. }}<br><br>
+
+<b><tt>#ifndef </tt></b>&lt;filename&gt;<b><tt>_INCLUDED</tt></b><br>
+<b><tt>#define </tt></b>&lt;filename&gt;<b><tt>_INCLUDED</tt></b><br><br>
+
+{{ The contents of the file }}<br><br>
+
+<b><tt>#endif /* </tt></b>&lt;filename&gt;<b><tt>_INCLUDED */</tt></b>
+</blockquote>
+
+<p>
+The header file is the first place that a reader goes for
+information about procedures, structures, constants, etc., so ensure that
+every procedure and structure has a comment that says what it does. Divide
+procedures into meaningful groups set off by some distinguished form of
+comment.
+
+<h3><a name="Source"></a>Source (<b><tt>.c</tt></b> files)</h3>
+
+<p>
+After the initial comments, arrange C files in the following order:
+
+<blockquote><ol>
+<li><b><tt>#include</tt></b> statements
+<li>Exported data declarations
+<li>Explicit externs (if necessary)
+<li>Forward declarations of procedures
+<li>Private data declarations
+<li>Exported procedures
+<li>Private procedures
+</ol></blockquote>
+
+<p>
+Be flexible about the order of the declarations if necessary to improve
+readability. Many older files don't follow this order, often without good
+reason.
+
+<hr>
+
+<h2><a name="Conventions"></a>Ghostscript conventions</h2>
+
+<h3><a name="Specific_names"></a>Specific names</h3>
+
+<p>
+The Ghostscript code uses certain names consistently for certain kinds of
+values. Some of the commonest and least obvious are these two:
+
+<h4><a name="code"></a><b><tt>code</tt></b></h4>
+
+<blockquote>
+A value to be returned from a procedure:
+
+<table cellpadding=0 cellspacing=0>
+<tr valign=top> <td align=right>&lt; 0
+ <td>&nbsp;&nbsp;&nbsp;&nbsp;
+ <td>An error code defined in
+<a href="../src/gserrors.h">gserrors.h</a>
+(or <a href="../src/errors.h">errors.h</a>)
+<tr valign=top> <td align=right>0
+ <td>&nbsp;
+ <td>Normal return
+<tr valign=top> <td align=right>&gt; 0
+ <td>&nbsp;
+ <td>A non-standard but successful return (which must be documented, preferably with the procedure's prototype)
+</table>
+
+</blockquote>
+
+<h4><a name="status"></a><b><tt>status</tt></b></h4>
+
+<blockquote>
+A value returned from a stream procedure:
+
+<table cellpadding=0 cellspacing=0>
+<tr valign=top> <td align=right>&lt; 0
+ <td>&nbsp;&nbsp;&nbsp;&nbsp;
+ <td>An exceptional condition as defined in
+<a href="../src/scommon.h">scommon.h</a>
+<tr valign=top> <td align=right>0
+ <td>&nbsp;
+ <td>Normal return (or, from the "<b><tt>process</tt></b>" procedure, means that more input is needed)
+<tr valign=top> <td align=right>1
+ <td>&nbsp;
+ <td>More output space is needed (from the "<b><tt>process</tt></b>" procedure)
+</table>
+</blockquote>
+
+<h3><a name="Structure_type_descriptors"></a>Structure type descriptors</h3>
+
+<p>
+The Ghostscript memory manager requires run-time type information for every
+structure. (We don't document this in detail here: see the <a
+href="Develop.htm#Structure_descriptors">Structure descriptors</a> section
+of the developer documentation for details.) Putting the descriptor for a
+structure next to the structure definition will help keep the two
+consistent, so immediately after the definition of a structure
+<b><tt>xxx_s</tt></b>, define its structure descriptor:
+
+<blockquote>
+<b><tt>struct xxx_s {</tt></b><br>
+&nbsp;&nbsp;&nbsp;... members ...<br>
+<b><tt>};</tt></b><br>
+<b><tt>#define private_st_xxx()&nbsp;&nbsp;/* in </tt></b>&lt;filename&gt;<tt><b>.c */\</tt></b><br>
+<b><tt>&nbsp;&nbsp;gs_private_st_</tt></b>&lt;whatever&gt;<b><tt>(st_xxx, xxx_t,\</tt></b><br>
+<b><tt>&nbsp;&nbsp;&nbsp;&nbsp;"xxx_t", xxx_enum_ptrs, xxx_reloc_ptrs,\</tt></b><br>
+<b><tt>&nbsp;&nbsp;&nbsp;&nbsp;</tt></b>... additional parameters as needed ...<b><tt>)</tt></b>
+</blockquote>
+
+<p>
+The file that implements operations on this structure
+(&lt;filename&gt;<b><tt>.c</tt></b>) should then include, near the
+beginning, the line:
+
+<blockquote>
+<b><tt>private_st_xxx();</tt></b>
+</blockquote>
+
+<p>
+In much existing code, structure descriptors are declared as
+<b><tt>public</tt></b>, which allows clients to allocate instances of the
+structure directly. We now consider this bad design. Instead, structure
+descriptors should always be <b><tt>private</tt></b>; the implementation
+file should provide one or more procedures for allocating instances, e.g.,
+
+<blockquote>
+<b><tt>xxx_t *gs_xxx_alloc(P1(gs_memory_t *mem));</tt></b>
+</blockquote>
+
+<p>
+If it is necessary to make a structure descriptor public, it should be
+declared in its clients as
+
+<blockquote>
+<b><tt>extern_st(st_xxx);</tt></b>
+</blockquote>
+
+<h3><a name="Objects"></a>"Objects"</h3>
+
+<p>
+Ghostscript makes heavy use of object-oriented constructs, including
+analogues of classes, instances, subclassing, and class-associated
+procedures. However, these constructs are implemented in C rather than C++,
+for two reasons:
+
+<ul>
+
+<li>The first Ghostscript code was written in 1986, long before C++ was
+codified or was well supported by tools. Even today, C++ tools rarely
+support C++ as well as C tools support C.
+
+<li>C++ imposes its own implementations for virtual procedures, inheritance,
+run-time type information, and (to some extent) memory management.
+Ghostscript requires use of its own memory manager, and also sometimes
+requires the ability to change the virtual procedures of an object
+dynamically.
+
+</ul>
+
+<h4>Classes</h4>
+
+<p>
+The source code representation of a class is simply a
+<b><tt>typedef</tt></b> for a C <b><tt>struct</tt></b>. See <a
+href="C-style.htm#Structures">Structures</a>, above, for details.
+
+<h4>Procedures</h4>
+
+<p>
+Ghostscript has no special construct for non-virtual procedures associated
+with a class. In some cases, the <b><tt>typedef</tt></b> for the class is
+in a header file but the <b><tt>struct</tt></b> declaration is in the
+implementation code file: this provides an extra level of opaqueness, since
+clients then can't see the representation and must make all accesses through
+procedures. You should use this approach in new code, if it doesn't
+increase the size of the code too much or require procedure calls for very
+heavily used accesses.
+
+<p>
+Ghostscript uses three different approaches for storing and accessing
+virtual procedures, plus a fourth one that is recommended but not currently
+used. For exposition, we assume the class (type) is named
+<b><tt>xxx_t</tt></b>, it has a virtual procedure
+<b><tt>void&nbsp;(*virtu)(P1(xxx_t&nbsp;*))</tt></b>, and we have a variable
+declared as <b><tt>xxx_t&nbsp;*pxx</tt></b>.
+
+<ol>
+
+<li>The procedures are stored in a separate, constant structure of type
+<b><tt>xxx_procs</tt></b>, of which <b><tt>virtu</tt></b> is a member. The
+structure definition of <b><tt>xxx_t</tt></b> includes a member defined as
+<b><tt>const&nbsp;xxx_procs&nbsp;*procs</tt></b> (always named
+<b><tt>procs</tt></b>). The construct for calling the virtual procedure is
+<b><tt>pxx->procs->virtu(pxx)</tt></b>.
+
+<li>The procedures are defined in a structure of type
+<b><tt>xxx_procs</tt></b> as above. The structure definition of
+<b><tt>xxx_t</tt></b> includes a member defined as
+<b><tt>xxx_procs&nbsp;procs</tt></b> (always named <b><tt>procs</tt></b>).
+The construct for calling the virtual procedure is
+<b><tt>pxx->procs.virtu(pxx)</tt></b>.
+
+<li>The procedures are not defined in a separate structure: each procedure
+is a separate member of <b><tt>xxx_t</tt></b>. The construct for calling
+the virtual procedure is <b><tt>pxx->virtu(pxx)</tt></b>.
+
+<li>The procedures are defined in a structure of type
+<b><tt>xxx_procs</tt></b> as above. The structure definition of
+<b><tt>xxx_t</tt></b> includes a member defined as
+<b><tt>xxx_procs&nbsp;procs[1]</tt></b> (always named
+<b><tt>procs</tt></b>). The construct for calling the virtual procedure is
+again <b><tt>pxx->procs->virtu(pxx)</tt></b>.
+
+</ol>
+
+<p>
+Note that in approach 1, the procedures are in a shared constant structure;
+in approaches 2 - 4, they are in a per-instance structure that can be
+changed dynamically, which is sometimes important.
+
+<p>
+In the present Ghostscript code, approach 1 is most common, followed by 2
+and 3; 4 is not used at all. For new code, you should use 1 or 4: that way,
+all virtual procedure calls have the same form, regardless of whether the
+procedures are shared and constant or per-instance and mutable.
+
+<h4>Subclassing</h4>
+
+<p>
+Ghostscript's class mechanism allows for subclasses that can add data
+members, or can add procedure members if approach 1 or 3 (above) is used.
+Since C doesn't support subclassing, we use a convention to accomplish it.
+In the example below, <b><tt>gx_device</tt></b> is the root class; it has a
+subclass <b><tt>gx_device_forward</tt></b>, which in turn has a subclass
+<b><tt>gx_device_null</tt></b>. First we define a macro for all the members
+of the root class, and the root class type. (As for structures in general,
+classes need a structure descriptor, as discussed in <a
+href="#Structures">Structures</a> above: we include these in the examples
+below.)
+
+<blockquote><b><tt>
+#define gx_device_common\<br>
+&nbsp;&nbsp;&nbsp;&nbsp;type1 member1;\<br>
+&nbsp;&nbsp;&nbsp;&nbsp;</tt></b>...<b><tt><br>
+&nbsp;&nbsp;&nbsp;&nbsp;typeN memberN<br>
+<br>
+typedef struct gx_device_s {<br>
+&nbsp;&nbsp;&nbsp;&nbsp;gx_device_common;<br>
+} gx_device;<br>
+<br>
+#define private_st_gx_device()&nbsp;&nbsp;/* in gsdevice.c */\<br>
+&nbsp;&nbsp;gs_private_st_</tt></b>&lt;whatever&gt;<b><tt>(st_gx_device, gx_device,\<br>
+&nbsp;&nbsp;&nbsp;&nbsp;"gx_device", device_enum_ptrs, device_reloc_ptrs,\<br>
+&nbsp;&nbsp;&nbsp;&nbsp;</tt></b>... additional parameters as needed ...<b><tt>)</tt></b>
+</tt></b></blockquote>
+
+<p>
+We then define a similar macro and type for the subclass.
+
+<blockquote><b><tt>
+#define gx_device_forward_common\<br>
+&nbsp;&nbsp;&nbsp;&nbsp;gx_device_common;\<br>
+&nbsp;&nbsp;&nbsp;&nbsp;gx_device *target<br>
+<br>
+typedef struct gx_device_forward_s {<br>
+&nbsp;&nbsp;&nbsp;&nbsp;gx_device_forward_common;<br>
+} gx_device_forward;<br>
+<br>
+#define private_st_device_forward()&nbsp;&nbsp;/* in gsdevice.c */\<br>
+&nbsp;&nbsp;gs_private_st_suffix_add1(st_device_forward, gx_device_forward,\<br>
+&nbsp;&nbsp;&nbsp;&nbsp;"gx_device_forward", device_forward_enum_ptrs, device_forward_reloc_ptrs,\<br>
+&nbsp;&nbsp;&nbsp;&nbsp;gx_device, target)
+</tt></b></blockquote>
+
+<p>
+Finally, we define a leaf class, which doesn't need a macro because we don't
+currently subclass it. (We can create the macro later if needed, with no
+changes anywhere else.) In this particular case, the leaf class has no
+additional data members, but it could have some.
+
+<blockquote><b><tt>
+typedef struct gx_device_null_s {<br>
+&nbsp;&nbsp;&nbsp;&nbsp;gx_device_forward_common;<br>
+};<br>
+<br>
+#define private_st_device_null()&nbsp;&nbsp;/* in gsdevice.c */\<br>
+&nbsp;&nbsp;gs_private_st_suffix_add0_local(st_device_null, gx_device_null,\<br>
+&nbsp;&nbsp;&nbsp;&nbsp;"gx_device_null", device_null_enum_ptrs, device_null_reloc_ptrs,\<br>
+&nbsp;&nbsp;&nbsp;&nbsp;gx_device_forward)
+</tt></b></blockquote>
+
+<p>
+Note that the above example is <strong>not</strong> the actual definition of
+the <b><tt>gx_device</tt></b> structure type: the actual type has some
+additional complications because it has a finalization procedure. See <a
+href="../src/gxdevcli.h">src/gxdevcli.h</a> for the details.
+
+<p>
+If you add members to a root class (such as <b><tt>gx_device</tt></b> in
+this example), or change existing members, do this in the
+<b><tt>gx_device_common</tt></b> macro, not the <b><tt>gx_device</tt></b>
+structure definition. Similarly, to change the
+<b><tt>gx_device_forward</tt></b> class, modify the
+<b><tt>gx_device_forward_common</tt></b> macro, not the structure
+definition. Only change the structure definition if the class is a leaf
+class (one with no <b><tt>_common</tt></b> macro and no possibility of
+subclassing), like <b><tt>gx_device_null</tt></b>.
+
+<h3><a name="Error_handling"></a>Error handling</h3>
+
+<p>
+Every caller should check for error returns and, in general, propagate them
+to <b>its</b> callers. By convention, nearly every procedure returns an
+<b><tt>int</tt></b> to indicate the outcome of the call:
+
+<blockquote><table cellpadding=0 cellspacing=0>
+<tr valign=top> <td align=right>&lt; 0
+ <td>&nbsp;&nbsp;&nbsp;&nbsp;
+ <td>Error return
+<tr valign=top> <td align=right>0
+ <td>&nbsp;
+ <td>Normal return
+<tr valign=top> <td align=right>&gt; 0
+ <td>&nbsp;
+ <td>Non-error return other than the normal case
+</table></blockquote>
+
+<p>
+To make a procedure generate an error and return it, as opposed to
+propagating an error generated by a lower procedure, you should use
+
+<blockquote>
+<b><tt>return_error(</tt></b><em>error_number</em><b><tt>);</tt></b>
+</blockquote>
+
+<p>
+Sometimes it is more convenient to generate the error in one place and
+return it in another. In this case, you should use
+
+<blockquote>
+<b><tt>code = gs_note_error(</tt></b><em>error_number</em><b><tt>);</tt></b><br>
+...<br>
+<b><tt>return code;</tt></b>
+</blockquote>
+
+<p>
+In executables built for debugging, the <b><tt>-E</tt></b> (or
+<b><tt>-Z#</tt></b>) command line switch causes <b><tt>return_error</tt></b>
+and <b><tt>gs_note_error</tt></b> to print the error number and the source
+file and line: this is often helpful for identifying the original cause of
+an error.
+
+<p>
+See the file <a href="../src/gserrors.h">src/gserrors.h</a> for the error
+return codes used by the graphics library, most of which correspond directly
+to PostScript error conditions.
+
+<!-- [2.0 end contents] ==================================================== -->
+
+<!-- [3.0 begin visible trailer] =========================================== -->
+<hr>
+
+
+<p>
+<small>
+This software is provided AS-IS with no warranty, either express or
+implied.
+
+This software is distributed under license and may not be copied,
+modified or distributed except as expressly authorized under the terms
+of the license contained in the file LICENSE in this distribution.
+</small>
+
+<p>
+<small>Copyright &copy; 1996-2002 artofcode LLC.
+All rights reserved.</small>
+
+
+<p>
+<small>Ghostscript version 7.07, 17 May 2003
+
+<!-- [3.0 end visible trailer] ============================================= -->
+
+</body>
+</html>