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<TITLE>Notes On Writing Portable Programs In C</TITLE>
<META NAME="description" CONTENT="Notes On Writing Portable Programs In C (June 1990, 5th Revision) ">
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<BR> <P>
<P>
<H1 ALIGN=CENTER>Notes On Writing Portable Programs In C</H1><BR>
<H2>(June 1990, 5th Revision)</H2>
<P ALIGN=CENTER><STRONG>A. Dolenc <BR>
A. Lemmke
<A NAME="tex2html1" HREF="#6">[+]</A>
<BR> and <BR>
D. Keppel
<A NAME="tex2html2" HREF="#7">[+]</A>
</STRONG></P><P>
<P>
<P><H2><A NAME="SECTION00010000000000000000">Contents</A></H2>
<UL><A NAME="CHILD_LINKS"> </A>
<LI> <A NAME="tex2html24" HREF="portableC.html#SECTION00020000000000000000">Foreword</A>
<LI> <A NAME="tex2html25" HREF="portableC.html#SECTION00030000000000000000">Introduction</A>
<LI> <A NAME="tex2html26" HREF="portableC.html#SECTION00040000000000000000">Standardization Efforts</A>
<UL>
<LI> <A NAME="tex2html27" HREF="portableC.html#SECTION00041000000000000000">ANSI C</A>
<UL>
<LI> <A NAME="tex2html28" HREF="portableC.html#SECTION00041100000000000000">Translation limits</A>
<LI> <A NAME="tex2html29" HREF="portableC.html#SECTION00041200000000000000">Unspecified and undefined behaviour</A>
</UL>
<LI> <A NAME="tex2html30" HREF="portableC.html#SECTION00042000000000000000">POSIX</A>
</UL>
<LI> <A NAME="tex2html31" HREF="portableC.html#SECTION00050000000000000000">Preprocessors</A>
<LI> <A NAME="tex2html32" HREF="portableC.html#SECTION00060000000000000000">The Language</A>
<UL>
<LI> <A NAME="tex2html33" HREF="portableC.html#SECTION00061000000000000000">The syntax</A>
<LI> <A NAME="tex2html34" HREF="portableC.html#SECTION00062000000000000000">The semantics</A>
</UL>
<LI> <A NAME="tex2html35" HREF="portableC.html#SECTION00070000000000000000">Unix flavours: System V and BSD</A>
<LI> <A NAME="tex2html36" HREF="portableC.html#SECTION00080000000000000000">Header Files</A>
<UL>
<LI> <A NAME="tex2html37" HREF="portableC.html#SECTION00081000000000000000"><TT>ctype.h</TT></A>
<LI> <A NAME="tex2html38" HREF="portableC.html#SECTION00082000000000000000"><TT>fcntl.h</TT> and <TT>sys/file.h</TT></A>
<LI> <A NAME="tex2html39" HREF="portableC.html#SECTION00083000000000000000"><TT>errno.h</TT></A>
<LI> <A NAME="tex2html40" HREF="portableC.html#SECTION00084000000000000000"><TT>math.h</TT></A>
<LI> <A NAME="tex2html41" HREF="portableC.html#SECTION00085000000000000000"><TT>strings.h</TT> vs. <TT>string.h</TT></A>
<LI> <A NAME="tex2html42" HREF="portableC.html#SECTION00086000000000000000"><TT>time.h</TT> and <TT>types.h</TT></A>
<LI> <A NAME="tex2html43" HREF="portableC.html#SECTION00087000000000000000"><TT>varargs.h</TT> vs. <TT>stdarg.h</TT></A>
</UL>
<LI> <A NAME="tex2html44" HREF="portableC.html#SECTION00090000000000000000">Run-time Library</A>
<LI> <A NAME="tex2html45" HREF="portableC.html#SECTION000100000000000000000">Compiler limitations</A>
<LI> <A NAME="tex2html46" HREF="portableC.html#SECTION000110000000000000000">Using floating-point numbers</A>
<UL>
<LI> <A NAME="tex2html47" HREF="portableC.html#SECTION000111000000000000000">Machine constants</A>
<LI> <A NAME="tex2html48" HREF="portableC.html#SECTION000112000000000000000">Floating-point arguments</A>
<LI> <A NAME="tex2html49" HREF="portableC.html#SECTION000113000000000000000">Floating-point arithmetic</A>
<LI> <A NAME="tex2html50" HREF="portableC.html#SECTION000114000000000000000">Exceptions</A>
</UL>
<LI> <A NAME="tex2html51" HREF="portableC.html#SECTION000120000000000000000">VMS</A>
<UL>
<LI> <A NAME="tex2html52" HREF="portableC.html#SECTION000121000000000000000">File specifications</A>
<LI> <A NAME="tex2html53" HREF="portableC.html#SECTION000122000000000000000">Miscellaneous</A>
</UL>
<LI> <A NAME="tex2html54" HREF="portableC.html#SECTION000130000000000000000">General Guidelines</A>
<UL>
<LI> <A NAME="tex2html55" HREF="portableC.html#SECTION000131000000000000000">Machine architectures, Type compatibility, Pointers, etc.</A>
<LI> <A NAME="tex2html56" HREF="portableC.html#SECTION000132000000000000000">Compiler differences</A>
<LI> <A NAME="tex2html57" HREF="portableC.html#SECTION000133000000000000000">Files</A>
<LI> <A NAME="tex2html58" HREF="portableC.html#SECTION000134000000000000000">Miscellaneous</A>
</UL>
<LI> <A NAME="tex2html59" HREF="portableC.html#SECTION000140000000000000000">Acknowledgements</A>
<LI> <A NAME="tex2html60" HREF="portableC.html#SECTION000150000000000000000">Trademarks</A>
<LI> <A NAME="tex2html61" HREF="portableC.html#SECTION000160000000000000000">References</A>
<LI> <A NAME="tex2html62" HREF="portableC.html#SECTION000170000000000000000"> About this document ... </A>
</UL>
<P>
<H1><A NAME="SECTION00020000000000000000">Foreword</A></H1>
<P>
A few words about the intended audience before we begin. This document
is mainly for those who have <B>never</B> ported a program to another
platform -- a specific hardware and software environment --
and, evidently, for those who plan to write large systems which
must be used across different vendor machines.
<P>
If you have done some porting before you may not find the information herein
very useful.
<P>
We suggest that [<A HREF="portableC.html#kn:style">Can89</A>] be read in conjunction with this
document<A NAME="tex2html3" HREF="#326">[+]</A>.
Submitters to the News group <B>comp.lang.c</B> have repeatedly recommended
[<A HREF="portableC.html#kn:MH">Hor90</A>, <A HREF="portableC.html#kn:AK">Koe89</A>]<A NAME="tex2html4" HREF="#19">[+]</A>.
<P>
<B>Disclaimer:</B> The code fragments presented herein
are intended to make applications
``more'' portable, meaning that they may fail with some compilers
and/or environments.
<P>
This file can be obtained via anonymous ftp from <EM>sauna.hut.fi
[130.233.251.253]</EM> in ~ftp/pub/CompSciLab/doc</EM>. The files
<EM>portableC.tex</EM>, <EM>portableC.bib</EM> and <EM>portableC.ps.Z</EM>
are the LaTeX, BibTeX and the compressed PostScript, respectively.
<P>
<H1><A NAME="SECTION00030000000000000000">Introduction</A></H1>
<P>
The aim of this document is to collect the experience of several people
who have had to write and/or port programs in C to more than one platform.
<P>
In order to keep this document within reasonable bounds we must
restrict ourselves to programs which must execute under
Unix-like
operating systems and those which implement a reasonable Unix-like
environment. The only exception we will consider is
VMS.
<P>
A wealth of information can be obtained from programs which have been
written to run on several platforms. This is the case of
publicly available software such as
developed by the Free Software
Foundation and the MIT X Consortium.
<P>
When discussing portability one focuses on two issues:
<DL ><DT><DD><B>The language,</B> which includes the preprocessor and the syntax and the
semantics of the language.
<P>
<DT><DD><B>The environment,</B> which includes the location and contents of header
files and the run-time library.
<P>
</DL>
<P>
We include in our discussions the standardization efforts of
the language and the environment. Special attention will be given
to floating-point representations and arithmetic, to limitations
of specific compilers, and to VMS.
<P>
Our main focus will be <EM>boiler-plate</EM> problems.
System programming<A NAME="tex2html5" HREF="#32">[+]</A>
and twisted code associated with bizarre interpretations of [<A HREF="portableC.html#kn:ansi">X3J88</A>]
- henceforth refered to as the Standard -
will not be extensively covered in this document<A NAME="tex2html6" HREF="#34">[+]</A>.
<P>
<H1><A NAME="SECTION00040000000000000000">Standardization Efforts</A></H1>
<P>
All standards have a good and an evil side. Due to the nature of this
document we are forced to focus our attention on the later.
<P>
The American National Standards Institute (ANSI) has recently approved
of a standard for the C programming language [<A HREF="portableC.html#kn:ansi">X3J88</A>]. The Standard
concentrates on the syntax and semantics of the language and specifies
a minimum environment (the name and contents of some header files and
the specification of some run-time library functions).
<P>
Copies of the ANSI C Standard can be obtained from the following address:
American National Standards Institute<BR>
Sales Department<BR>
1430 Broadway<BR>
New York, NY 10018<BR>
(Voice) (212) 642-4900<BR>
(Fax) (212) 302-1286<BR>
<P>
<H2><A NAME="SECTION00041000000000000000">ANSI C</A></H2>
<P>
<H3><A NAME="SECTION00041100000000000000">Translation limits</A></H3>
<P>
We first bring to attention the fact that the Standard states some
environmental limits. These limits are <EM>lower bounds</EM>, meaning that
a correct (compliant) compiler may refuse to compile an otherwise correct
program which exceeds one of those limits<A NAME="tex2html7" HREF="#328">[+]</A>.
<P>
Below are the limits which we judge to be the most important. The ones
related to the preprocessor are listed first.
<P>
<UL>
<LI> <EM>8 nesting levels of conditional inclusion.</EM>
<LI> <EM>8 nesting levels for <TT>#included</TT> files.</EM>
<LI> <EM>32 nesting levels of parenthesized expressions within
a full expression.</EM> This will probably occur when using macros.
<LI> <EM>1024 macro identifiers simultaneously.</EM> Can happen if
one includes too many header files.
<LI> <EM>509 characters in a logical source line.</EM>
This is a serious restriction if it applies <EM>after</EM> preprocessing.
Since a macro
expansion always results in one line this affects the maximum
size of a macro. It is unclear what the Standard means by a logical
source line in this context and in most implementations this limit
will probably apply em before macro expansion.
<LI> <EM>6 significant initial characters in an external identifier.</EM>
Usually this constraint is imposed by the environment, e.g. the linker,
and not by the compiler.
<LI> <EM>127 members in a single structure or union.</EM>
<LI> <EM>31 parameters in one function call.</EM> This may cause trouble
with functions which accept a variable number of arguments. Therefore,
it is advisable that when designing such functions that either the
number of parameters be kept within reasonable bounds or that alternative
interfaces be supplied, e.g. using arrays.
<P>
</UL>
<P>
It is really unfortunate that some of these limits may force a programmer
to code in a less elegant way. We are of the opinion that
the remaining limits stated in the Standard can usually be obeyed
if one follows ``good'' programming practices.
<P>
However, these limits may break programs which <EM>generate</EM> C code
such as compiler-compilers and many C++ compilers.
<P>
<H3><A NAME="SECTION00041200000000000000">Unspecified and undefined behaviour</A></H3>
<P>
The following are examples of unspecified and undefined behaviour:
<P>
<OL>
<LI> The order in which the function designator and the arguments
in a function call are evaluated.
<LI> The order in which the preprocessor concatenation operators
<TT>#</TT> and <TT>##</TT> are evaluated during macro substitution.
<LI> The representation of floating types.
<LI> An identifier is used that is not visible in the current scope.
<LI> A pointer is converted to other than an integral or pointer type.
<P>
</OL>
<P>
The list is long. One of the main reasons for explicitly defining what
is <EM>not</EM> covered by the Standard is to allow the implementor of the
C environment to make use the most efficient alternative.
<P>
<H2><A NAME="SECTION00042000000000000000">POSIX</A></H2>
<P>
The objective of the POSIX working group P1003.1 is to define a common
interface for UNIX. Granted, the ANSI C standard does specify the
contents of some header files and the behaviour of some library functions
but it falls short of defining a usefull environment. This is the
task of P1003.1.
<P>
We do not know how far P1003.1 addresses the problems presented in this
document as at the moment we lack proper documentation.
Hopefully, this will be corrected in a future release of this document.
<P>
<H1><A NAME="SECTION00050000000000000000">Preprocessors</A></H1>
<P>
Preprocessors may present different behaviour in the following:
<P>
<OL>
<LI> The interpretation of the <B>-I</B> command option can differ from
one system to another. Besides, it is not covered by the Standard. For
example, the directive <TT>#include ``dir/file.h''</TT> in conjunction with
<B>-I..</B> would cause most preprocessors in a Unix-like environment
to search for <TT>file.h</TT> in <TT>../dir</TT> but under VMS <TT>file.h</TT>
is only searched for in the subdirectory <TT>dir</TT> in the current
working directory.
<LI> We would <B>not</B> trust the following to work on <B>all</B>
preprocessors:
<P>
<PRE>#define D define
#D this that</PRE>
<P>
The Standard does not allow such a syntax (see section 3.8.3 §20
in [<A HREF="portableC.html#kn:ansi">X3J88</A>]).
<LI> Directives are very much the same in all preprocessors, except that
some preprocessors may not know about the <TT>defined</TT> operator in a
<TT>#if</TT> directive nor about the <TT>#pragma</TT> directive.
<P>
The <TT>#pragma</TT> directive should pose no problems even to old
preprocessors <EM>if it comes indented</EM><A NAME="tex2html8" HREF="#330">[+]</A>.
Furthermore, it is advisable to
enclose them with <TT>#ifdef</TT>'s in order to document under which
platform they make sense:
<PRE>#ifdef <platform-specific-symbol>
#pragma ...
#endif</PRE>
<LI> Concatenation of symbols has two variants. One is the old K&R style
which simply relied on the fact that the preprocessor substituted
comments such as <TT>/**/</TT> for nothing. Obviously, that does not result
in concatenation
if the preprocessor includes a space in the output.
The ANSI C Standard defines the operators <TT>##</TT> and
(implicit) concatenation of adjacent strings. Since both
styles are a fact of life it is useful to include the following in one's
header files<A NAME="tex2html9" HREF="#331">[+]</A>:
<P>
<PRE>#ifdef __STDC__
# define GLUE(a,b) a##b
#else
# define GLUE(a,b) a/**/b
#endif</PRE>
<P>
If needed, one could define similar macros to <TT>GLUE</TT> several arguments
<A NAME="tex2html10" HREF="#332">[+]</A>.
<LI> Some preprocessors perform token substitution within quotes while others
do not. Therefore, this is intrinsicly non-portable. The Standard
disallows it but provides mechanism to obtain the same results. The
following should work with ANSI-compliant preprocessors or with the
ones that which perform token substitution within quotes:
<P>
<PRE>#ifdef __STDC__
# define MAKESTRING(s) # s
#else
# define MAKESTRING(s) "s"
#endif</PRE>
<P>
</OL>
<P>
There are good publicly available preprocessors which are ANSI C compliant.
One such preprocessor is the one distributed with the X
Window System developed by the MIT X Consortium.
<P>
Take note of <TT>#pragma</TT> directives which
alter the semantics of the program and consider the case when they
are not recognized by a particular compiler. Evidently,
if the behaviour of the program relies on their correct interpretation
then, in order for the program to be portable, all target platforms
must recognize them properly.
<P>
Finally, we must add that the Standard has fortunately included
a <TT>#error</TT> directive with obvious semantics. Indent the <TT>#error</TT>
since old preprocessors do not recognize it.
<P>
<H1><A NAME="SECTION00060000000000000000">The Language</A></H1>
<P>
<H2><A NAME="SECTION00061000000000000000">The syntax</A></H2>
<P>
The syntax defined in the Standard is a <EM>superset</EM> of the one defined in K&R.
It follows that if one restricts oneself to the former there should be no problems
with an ANSI C compliant compiler. The Standard extends the syntax with the
following:
<P>
<OL>
<LI> The inclusion of the keywords <B>const</B> and
<B>volatile</B>.
<LI> The ellipsis (``...'') notation to indicate a variable number
of arguments.
<LI> Function prototypes.
<LI> Trigraph notation for specifying ``wide'' character strings.
<P>
</OL>
<P>
We encourage the use of the reserved words <B>const</B> and <B>volatile</B>
since they aid in documenting the code.
It is useful to add the following to one's header files if the code must
be compiled by an non-conforming compiler as well:
<PRE>#ifndef __STDC__
# define const
# define volatile
#endif</PRE>
<P>
However, one must then make sure that the behaviour of the application does not
depend on the presence of such keywords.
<P>
<H2><A NAME="SECTION00062000000000000000">The semantics</A></H2>
<P>
The syntax does not pose any problem with regard to interpretation because
it can be defined precisely. However, programming languages are always
described using a natural language, e.g. English, and this can lead to
different interpretations of the same text.
<P>
Evidently, [<A HREF="portableC.html#kn:KR">KR78</A>] does not provide an unambiguous definition
of the C language otherwise there would have been no need for a standard.
Although the Standard is much more precise,
there is still room for different interpretations in situations
such as <TT>f(p=&a, p=&b, p=&c)</TT>. Does this mean <TT>f(&a,&b,&c)</TT> or
<TT>f(&c,&c,&c)</TT>? Even ``simple'' cases such as <TT>a[i] = b[i++]</TT>
are compiler-dependent [<A HREF="portableC.html#kn:style">Can89</A>].
<P>
As stated in the Introduction we would like to exclude such topics.
The reader is instead directed to the USENET news group <B>comp.std.c</B>
or <B>comp.lang.c</B>
where such discussions take place and from where the above example
was taken. <EM>The Journal of C Language Translation</EM><A NAME="tex2html11" HREF="#115">[+]</A> could, perhaps,
be a good reference. Another possibility is to obtain a clarification
from the Standards Committee and the address is:
X3 Secretariat, CBEMA<BR>
311 1st St NW Ste 500<BR>
Washington DC, USA<BR>
<H1><A NAME="SECTION00070000000000000000">Unix flavours: System V and BSD</A></H1>
<P>
A long time ago (1969),
Unix said ``<TT>papa</TT>'' for the first time at AT&T
(then called Bell Laboratories, or Ma Bell for the
intimate) on a PDP-11. Everyone liked Unix very much and its widespread
use we see today is probably due to the relative simplicity
of its design and of its implementation (it is written, of course, mostly
in C).
<P>
However, these facts also contributed for each one to develop their own
dialect. In particular, the University of Berkeley at California distribute
the so-called BSD<A NAME="tex2html12" HREF="#122">[+]</A> Unix whereas
AT&T distribute (sell) System V Unix. All other vendors are descendants of
one of these major dialects.
<P>
The differences between these two major flavours should not upset most
application programs. In fact, we would even say that most differences are
just annoying.
<P>
BSD Unix has an enhanced signal handling capability and implements sockets.
However, <B>all</B> Unix flavours differ significantly in their raw i/o
interface (that is, <B>ioctl</B> system call) which should
be avoided if possible.
<P>
The reader interested in knowing more about the past and future of
Unix can consult [<A HREF="portableC.html#kn:unix1">Man89</A>, <A HREF="portableC.html#kn:unix2">Int90</A>].
<P>
<H1><A NAME="SECTION00080000000000000000">Header Files</A></H1>
<P>
Many useful system header files are in different places in different systems
or they define different symbols. We will assume henceforth that the
application has been developed on a BSD-like Unix and must be ported
to a System V-like Unix or VMS or an Unix-like system with header files
which comply to the Standard.
<P>
In the following sections, we show how to handle the most simple cases which
arise in practice. Some of the code which appears below was derived from
the header file <TT>Xos.h</TT> which is part of the X Window System distributed
by MIT. We have added changes, e.g. to support VMS.
<P>
Many header files are unprotected in many systems, notably those derived
from BSD version 4.2 and earlier. By unprotected we mean that an attempt
to include a header file more than once will either cause compilation
errors (e.g. due to recursive includes) or,
in some implementations, warnings from the preprocessor stating
that symbols are being redefined. It is good practice to protect header
files.
<P>
<H2><A NAME="SECTION00081000000000000000"><TT>ctype.h</TT></A></H2>
<P>
They provide the same functionality in all systems except that some
symbols must be renamed.
<P>
<PRE>#ifdef SYSV
# define _ctype_ _ctype
# define toupper _toupper
# define tolower _tolower
#endif</PRE>
<P>
Note however that the definitions in <TT><ctype.h></TT> are not portable across
character sets.
<P>
<H2><A NAME="SECTION00082000000000000000"><TT>fcntl.h</TT> and <TT>sys/file.h</TT></A></H2>
<P>
Many files which a BSD systems expects to find in the <TT>sys</TT>
directory are placed in <TT>/usr/include</TT> in System V. Other systems,
like VMS, do not even have a <TT>sys</TT> directory<A NAME="tex2html13" HREF="#335">[+]</A>.
<P>
The symbols used in the <TT>open</TT> function call are defined in different
header files in both types of systems:
<PRE>#ifdef SYSV
# include <fcntl.h>
#else
# include <sys/file.h>
#endif</PRE>
<P>
<H2><A NAME="SECTION00083000000000000000"><TT>errno.h</TT></A></H2>
<P>
The semantics of the error number may differ from one system to another
and the list may differ as well (e.g. BSD systems have more error numbers
than System V). Some systems, e.g. SunOS, define the global symbol
<B>errno</B> which will hold the last error detected by the run-time
library. This symbol is not available in most systems, although the
Standard requires that such a symbol be defined (see
section 4.1.3 of [<A HREF="portableC.html#kn:ansi">X3J88</A>]).
<P>
The most portable way to print error messages is to use <B>perror</B>.
<P>
<H2><A NAME="SECTION00084000000000000000"><TT>math.h</TT></A></H2>
<P>
System V has more definitions in this header file than BSD-like
systems. The corresponding library has more functions as well. This header
file is unprotected under VMS and Cray, and that case we must do-it-ourselves:
<PRE>#if defined(CRAY) || defined(VMS)
# ifndef __MATH__
# define __MATH__
# include <math.h>
# endif
#endif</PRE>
<P>
<H2><A NAME="SECTION00085000000000000000"><TT>strings.h</TT> vs. <TT>string.h</TT></A></H2>
<P>
Some systems cannot be treated as System V or BSD but are really a special
case, as one can see in the following:
<P>
<PRE>#ifdef SYSV
#ifndef SYSV_STRINGS
# define SYSV_STRINGS
#endif
#endif
#ifdef _STDH_ /* ANSI C Standard header files */
#ifndef SYSV_STRINGS
# define SYSV_STRINGS
#endif
#endif
#ifdef macII
#ifndef SYSV_STRINGS
# define SYSV_STRINGS
#endif
#endif
#ifdef vms
#ifndef SYSV_STRINGS
# define SYSV_STRINGS
#endif
#endif
#ifdef SYSV_STRINGS
# include <string.h>
# define index strchr
# define rindex strrchr
#else
# include <strings.h>
#endif</PRE>
<P>
As one can easily observe, System V-like Unix systems use different names
for <TT>index</TT> and <TT>rindex</TT> and place them in different header files.
Although VMS supports better System V features
it must be treated as a special case.
<P>
<H2><A NAME="SECTION00086000000000000000"><TT>time.h</TT> and <TT>types.h</TT></A></H2>
<P>
When using <TT>time.h</TT> one must also include <TT>types.h</TT>. The following
code does the trick:
<P>
<PRE>#ifdef macII
# include <time.h> /* on a Mac II we need this one as well */
#endif
#ifdef SYSV
# include <time.h>
#else
# ifdef vms
# include <time.h>
# else
# ifdef CRAY
# ifndef __TYPES__ /* it is not protected under CRAY */
# define __TYPES__
# include <sys/types.h>
# endif
# else
# include <sys/types.h>
# endif /* of ifdef CRAY */
# include <sys/time.h>
# endif /* of ifdef vms */
#endif</PRE>
<P>
The above is not sufficient in order for the code to be portable since
the structure which defines time values is not the same in all systems.
Different systems have vary in the way <TT>time_t</TT> values are represented.
The Standard, for instance, only requires that it be an arithmetic type.
Recognizing this difficulty, the Standard defines a function called
<TT>difftime</TT> to compute the difference between two time values of
type <TT>time_t</TT>, and <TT>mktime</TT> which takes a string and produces
a value of type <TT>time_t</TT>.
<P>
<H2><A NAME="SECTION00087000000000000000"><TT>varargs.h</TT> vs. <TT>stdarg.h</TT></A></H2>
<P>
In some systems the definitions in both header files
are contradictory. For instance, the following will produce compilation
errors under VMS<A NAME="tex2html14" HREF="#160">[+]</A>:
<PRE>#include <varargs.h>
#include <stdio.h></PRE>
<P>
This is because <TT><stdio.h></TT> includes <TT><stdarg.h></TT> which in turn
redefines all the symbols (<TT>va_start</TT>, <TT>va_end</TT>, etc.)
in <TT><varargs.h></TT>. The solution we adopt is to always include
<TT><varargs.h></TT> last and not define in the same module functions
which use <TT><varargs.h></TT> and functions which use the ellipsis notation.
<P>
<H1><A NAME="SECTION00090000000000000000">Run-time Library</A></H1>
<P>
<DL ><DT><STRONG>getlogin:</STRONG>
<DD> This one is not defined, e.g. under VMS.
In that case, one can always use <TT>getenv(``HOME'')</TT>.
<P>
<DT><STRONG>scanf:</STRONG>
<DD> Scanf can behave differently in different platforms because
it's descriptions, including the one in the Standard, allows for different
interpretations under some circumstances. The most portable input parser
is the one you write yourself.
<P>
<DT><STRONG>setjmp and longjmp:</STRONG>
<DD> Quoting anonymously
from <B>comp.std.c</B>, ``pre-X3.159 implementations of
setjmp and longjmp often did not meet the requirements of the Standard. Often
they didn't even meet their own documented specs. And the specs varied
from system to system. Thus it is wise not to depend too heavily on the
exact standard semantics for this facility...''.
<P>
In other words, it is not that you should <EM>not</EM> use them but
be careful if you do. Furthermore, the behaviour of a <B>longjmp</B>
invoked from a nested signal handler<A NAME="tex2html15" HREF="#340">[+]</A>
is undefined.
<P>
Finally, the symbols <TT>_setjmp</TT> and <TT>_longjmp</TT> are only defined
under SunOS, BSD, and HP-UX.
<P>
</DL><H1><A NAME="SECTION000100000000000000000">Compiler limitations</A></H1>
<P>
In practice, much too frequently one runs into several, unstated
compiler limitations:
<P>
<UL>
<LI> Some of these <EM>limitations</EM> are <EM>bugs</EM>. Many of these bugs
are in the optimizer and therefore when dealing with a new environment it is
best to explicitly disable optimization until one gets the application ``going''.
<LI> Some compilers cannot handle large modules or ``large''
statements<A NAME="tex2html16" HREF="#341">[+]</A>. Therefore,
it is advisable to keep the size of modules within reasonable bounds.
Besides, large modules are more cumbersome to edit and understand.
<P>
</UL><H1><A NAME="SECTION000110000000000000000">Using floating-point numbers</A></H1>
<P>
To say that the implementation of numerical algorithms
which exhibit the same behaviour across a wide variety of platforms is
difficult is an understatement. This section provides very little
help but we hope it is worth reading. Any additional suggestions
and information is <EM>very much</EM> appreciated as we would like
to expand this section.
<P>
<H2><A NAME="SECTION000111000000000000000">Machine constants</A></H2>
<P>
One problem when writing numerical algorithms is obtaining machine
constants. Typical values one needs are:
<P>
<UL>
<LI> The radix of the floating-point representation.
<LI> The number of digits in the floating-point significand expressed
in terms of the radix of the representation.
<LI> The number of bits reserved for the representation of the exponent.
<LI> The smallest positive floating-point number <I>eps</I> such that
(image not reproduced).
<LI> The smallest non-vanishing normalized floating-point power of the radix.
<LI> The largest finite<A NAME="tex2html17" HREF="#188">[+]</A> floating-point number.
<P>
</UL>
<P>
On Sun's they can be obtained in <TT><values.h></TT>.
The ANSI C Standard recommends that such constants be defined in the
header file <TT><float.h></TT>.
<P>
Sun's and standards apart, these values are not always readily available,
e.g. in
Tektronix workstations running UTek. One solution is to
use a modified version of a program which can be obtained from the network
called
<EM><B>machar</EM></B>. <B>Machar</B> is described in [<A HREF="portableC.html#kn:machar">Cod88</A>] and can
obtained by anonymous <EM>ftp</EM> from the
<EM>netlib</EM><A NAME="tex2html18" HREF="#342">[+]</A>.
<P>
It is straightforward to modify the C version of
<B>machar</B> to generate a C preprocessor
file which can be included directly by C programs.
<P>
There is also a publicly available
program called <EM>config.c</EM> which attempts to
determine many properties of the C compiler and machine that it is run on. This
program was submitted to <B>comp.sources.misc</B><A NAME="tex2html19" HREF="#343">[+]</A>.
<P>
<H2><A NAME="SECTION000112000000000000000">Floating-point arguments</A></H2>
<P>
In the days of K&R[<A HREF="portableC.html#kn:KR">KR78</A>] one was ``encouraged'' to use
<EM>float</EM> and <EM>double</EM> <BR>
interchangeably<A NAME="tex2html20" HREF="#207">[+]</A> since all expressions with
such data types where always evaluated using the <EM>double</EM> representation
- a real nightmare for those implementing efficient numerical algorithms
in C. This rule applied, in particular, to floating-point arguments and
for most compiler around it does not matter whether one defines the argument
as <EM>float</EM> or <EM>double</EM>.
<P>
According to the ANSI C Standard such programs will continue to exhibit the same
behaviour <EM>as long as one does not prototype the function</EM>. Therefore, when
prototyping functions make sure the prototype is included when the function
definition is compiled so the compiler can check if the arguments match.
<P>
<H2><A NAME="SECTION000113000000000000000">Floating-point arithmetic</A></H2>
<P>
Be careful when using the <TT>==</TT> and <TT>!=</TT> operators when comparing
floating types. Expressions such as
<TT>if (<EM>float_expr1</EM> == <EM>float_expr2</EM>)</TT>
will seldom be satisfied due to <EM>rounding errors</EM>.
To get a feeling about rounding errors, try evaluating the following
expression using your favourite C compiler[<A HREF="portableC.html#kn:fparith">KM86</A>]:
<BR>
(image not reproduced)
<BR>
<P>
Most computers will produce zero regardless if one uses <EM>float</EM> or
<EM>double</EM>. Although the <EM>absolute error</EM> is large, the <EM>relative
error</EM> is quite small and probably acceptable for many applications.
<P>
It is rather better to use expressions such as
(image not reproduced)
or
(image not reproduced)
(if
(image not reproduced)), where 0 < <I>K</I> < 1 is
a function of:
<OL>
<LI> The floating type, e.g. <EM>float</EM> or <EM>double</EM>,
<LI> the machine architecture (the machine constants defined in the
previous section), and
<LI> the precision of the input values and the rounding errors introduced
by the numerical method used.
</OL>
<P>
Other possibilities exist and the choice depends on the application.
<P>
The development of reliable and robust numerical algorithm is a very
difficult undertaking. Methods for certifying that the results are
correct within reasonable bounds must usually be implemented.
A reference such as [<A HREF="portableC.html#kn:NRC">PFTV88</A>] is always useful.
<P>
<UL>
<LI> Keep in mind that the <EM>double</EM> representation does not
necessarily increase the <EM>precision</EM>. Actually, in most implementations
the precision decreases but the <EM>range</EM> increases.
<LI> Do not use <EM>double</EM> unnecessarily since in most cases there is
a large performance penalty. Furthermore, there is no point in using higher
precision if the additional bits which will be computed are garbage anyway.
The precision one needs depends mostly on the precision of the input data
and the numerical method used.
<P>
</UL><H2><A NAME="SECTION000114000000000000000">Exceptions</A></H2>
<P>
Floating-point exceptions (overlow, underflow, division by zero, etc)
are not signaled automatically in some systems. In that case, they
must be explicitly enabled.
<P>
<EM>Always</EM> enable floating-point exceptions since they may be an
indication that the method is unstable. Otherwise, one must be sure
that such events do not affect the output.
<P>
<H1><A NAME="SECTION000120000000000000000">VMS</A></H1>
<P>
In this section we will report some common problems encountered when
porting a C program to a VMS environment and which we have not mentioned
in the previously.
<P>
<H2><A NAME="SECTION000121000000000000000">File specifications</A></H2>
<P>
Under VMS one can use two flavours of command interpreters: DCL and
DEC/Shell. The syntax of file specifications under DCL differs significantly
from the Unix syntax.
<P>
Some C run-time library functions in VMS which take file specifications
as arguments or return file specifications to the caller will accept
an additional argument indicating which syntax is preferred. It is
useful to use these run-time library functions via macros as follows:
<P>
<PRE>#ifdef VMS
#ifndef VMS_CI /* Which Command Interpreter flavour to use */
# define VMS_CI 0 /* 0 for DEC/Shell, 1 for DCL */
#endif
# define Getcwd(buff,siz) getcwd((buff),(siz),VMS_CI)
# define Getname(fd,buff) getname((fd),(buff),VMS_CI)
# define Fgetname(fp,buff) fgetname((fp),(buff),VMS_CI)
#else
# define Getcwd(buff,siz) getcwd((buff),(siz))
# define Getname(fd,buff) getname((fd),(buff))
# define Fgetname(fp,buff) fgetname((fp),(buff))
#endif /* of ifdef VMS */</PRE>
<P>
More pitfalls await the unaware who accept file specifications from the
user or take them from environment values (e.g. using the <B>getenv</B>
function).
<P>
<H2><A NAME="SECTION000122000000000000000">Miscellaneous</A></H2>
<P>
<DL ><DT><STRONG>end, etext, edata:</STRONG>
<DD> these global symbols are not available under
VMS.
<P>
<DT><STRONG><TT>Struct</TT> assignments:</STRONG>
<DD> VAX C allows assignment of structs if
the types of both sides have the same size. <EM>This is not a portable
feature.</EM>
<P>
<DT><STRONG>The system function:</STRONG>
<DD>
the <B>system</B> function under VMS has the same <EM>functionality</EM> as
the Unix version, except that one must take care that the command
interpreter provide also the same functionality. If the user is using
DCL then the application must send a DCL-like command.
<P>
<DT><STRONG>The linker:</STRONG>
<DD>
what follows applies only to modules stored in
libraries<A NAME="tex2html21" HREF="#253">[+]</A>.
If none of the global <EM>functions</EM> are explicitly used (referenced
by another module) then the
module is not linked <EM>at all</EM>. It does not matter whether one of the
global <EM>variables</EM> is used. As a side effect, the initialization
of variables is not done.
<P>
The easiest solution is to force the linker to add the
module using the /INCLUDE command modifier. Of course, there is the
possibility that the command line may exceed 256 characters...(*sigh*).
<P>
</DL><H1><A NAME="SECTION000130000000000000000">General Guidelines</A></H1>
<P>
<H2><A NAME="SECTION000131000000000000000">Machine architectures, Type compatibility, Pointers, etc.</A></H2>
<P>
<OL>
<LI> <B>Never</B> make any assumptions about the size of a given type,
especially pointers. [<A HREF="portableC.html#kn:style">Can89</A>] Statements such as
<TT>x &= 0177770</TT> make
implicit use of the size of <TT>x</TT>. If the intention is to clear the
lower three bits then it is best to use <TT>x &=
(image not reproduced)
07</TT>. The first
alternative will also clear the high order 16 bits if <TT>x</TT> is
32 bits wide.
<LI> In some architectures the byte order is inverted; these are called
<EM>little-endian</EM> versus <EM>big-endian</EM> architectures. This problem
is illustrated by the code below<A NAME="tex2html22" HREF="#347">[+]</A>:
<PRE>long int str[2] = {0x41424344, 0x0}; /* ASCII ``ABCD'' */
printf (``%s\n'', (char *)&str);</PRE>
<P>
A little-endian (e.g. VAX) will print ``<TT>DCBA</TT>''
whereas a big-endian (e.g. MC68000 microprocessors) will print ``<TT>ABCD</TT>''.
<LI> Beware of alignment constraints when allocating memory and using
pointers. Some
architectures restrict the addresses that certain operands
may be assigned to (that is, addresses of the form
(image not reproduced)
).
<LI> [<A HREF="portableC.html#kn:style">Can89</A>] Pointers to objects may have the same size but
different formats. This is illustrated by the code below:
<PRE>int *p = (int *) malloc(...); ... free(p);</PRE>
<P>
This code may malfunction in architectures where <TT>int*</TT> and <TT>char*</TT>
have different representations because <TT>free</TT> expects a pointer of
the latter type.
<LI> [<A HREF="portableC.html#kn:style">Can89</A>] Only the operators <TT>==</TT> and <TT>!=</TT> are
defined for all pointers of a given type. The remaining comparison
operators (<TT><</TT>, <TT><=</TT>, <TT>></TT>, and <TT>>=</TT>) can only be used when
both operands point into the same array or to the first element after
the array. The same applies to arithmetic operators on
pointers<A NAME="tex2html23" HREF="#283">[+]</A>.
<LI> <B>Never</B> redefine the <TT>NULL</TT> symbol. The NULL symbol should
always be the <EM>constant</EM> zero. A null pointer of a given type will
always compare equal to the <EM>constant</EM> zero, whereas comparison
with a variable with value zero or to some non-zero constant has
implementation defined behaviour.
<P>
A null pointer of a given type will always convert to a null
pointer of another type if implicit or explicit conversion is performed.
(See item 4 above.)
<P>
The contents of a null pointer may be anything the
implementor wishes and dereferencing it may cause strange things to
happen...
<P>
</OL><H2><A NAME="SECTION000132000000000000000">Compiler differences</A></H2>
<P>
<OL>
<LI> When <TT>char</TT> types are used in expressions most implementations
will treat them as <TT>unsigned</TT> <EM>but there are others which treat
them as</EM> <TT>signed</TT> (e.g. VAX C and HP-UX).
It is advisable to always cast them when used in arithmetic expressions.
<LI> Do not rely on the initialization of <TT>auto</TT> variables and
of memory returned by <TT>malloc</TT>.
<LI> Some compilers, e.g. VAX C, require that bit fields within <TT>struct</TT>s
be of type <TT>int</TT> or <TT>unsigned</TT>. Futhermore, the upper bound on
the length of the bit field may differ among different implementations.
<LI> The result of <TT>sizeof</TT> may be <TT>unsigned</TT>.
<P>
</OL><H2><A NAME="SECTION000133000000000000000">Files</A></H2>
<P>
<OL>
<LI> Keep files reasonably small in order not to upset some compilers.
<LI> File names should not exceed 14 characters (many System V derived
system impose this limit, whereas in BSD derived systems a limit
of 15 is usually the case).
In some implementations
this limit can be as low as 8 characters.
These limits are often <EM>not</EM>
imposed by the operating system but by system utilities such as <EM>ar</EM>.
<LI> Do not use special characters especially multiple dots (dots have
a very special meaning under VMS).
<P>
</OL><H2><A NAME="SECTION000134000000000000000">Miscellaneous</A></H2>
<P>
<DL ><DT><STRONG>Functions as arguments:</STRONG>
<DD> when calling functions passed as arguments
always dereference the pointer. In other words, if <TT>F</TT> is a pointer
to a function, use <TT>(*F)</TT> instead of simply <TT>(F)</TT> because some
compilers may not recognize the latter.
<P>
<DT><STRONG>System dependencies:</STRONG>
<DD> Isolate system dependent code in separate modules
and use conditional compilation.
<P>
<DT><STRONG>Utilities:</STRONG>
<DD> Utilities for compiling and linking such
as <B>Make</B> simplify considerably the task of moving an application from
one environment to another.
<P>
<DT><STRONG>Name space pollution:</STRONG>
<DD> Minimize the number of global symbols in the
application. One of the benefits is the lower probability that any
conflicts will arise with system-defined functions.
<P>
<DT><STRONG>String constants:</STRONG>
<DD> Do not modify string constants since many
implementations place them in read-only memory. Furthermore, that
is what the Standard requires -- and that is how a <EM>constant</EM>
should behave!
<P>
</DL><H1><A NAME="SECTION000140000000000000000">Acknowledgements</A></H1>
<P>
We are grateful for the help of Antti Louko (HTKK/Lsk) and Jari Helminen (HTKK)
in commenting and
correcting a previous draft of this document. We thank all the
contributors of USENET News groups <B>comp.std.c</B> and <B>comp.lang.c</B> from
where we have taken
a lot of information. Some information within was obtained from
[<A HREF="portableC.html#kn:HP">Hew88</A>].
<P>
<H1><A NAME="SECTION000150000000000000000">Trademarks</A></H1>
<P>
<P>
DEC, PDP-11, VMS and VAX are trademarks of Digital Equipment Corporation. <BR>
HP is a trademark of Hewlett-Packard, Inc.<BR>
MC68000 is a trademark of Motorola.<BR>
PostScript is a registred trademark of Adobe Systems, Inc.<BR>
Sun is a trademark of Sun Microsystems, Inc. <BR>
UNIX is a registred trademark of AT&T. <BR>
X Window System is a trademark of MIT.<BR>
<P>
<P><A NAME="SECTIONREF"><H2>References</H2></A><P>
<DL COMPACT>
<DT><A NAME="kn:style"><STRONG>Can89</STRONG></A><DD>
L.W. Cannon.
Recommended C Style and Coding Standards.
Technical report, November 1989.
<P>
<DT><A NAME="kn:machar"><STRONG>Cod88</STRONG></A><DD>
W. J. Cody.
Algorithm 665, MACHAR: A Subroutine to Dynamically Determine Machine
Parameters.
<EM>ACM Transactions on Mathematical Software</EM>, 14(4):303-311,
December 1988.
<P>
<DT><A NAME="kn:HP"><STRONG>Hew88</STRONG></A><DD>
Hewlett-Packard Company.
<EM>HP-UX Portability Guide</EM>, 1988.
<P>
<DT><A NAME="kn:MH"><STRONG>Hor90</STRONG></A><DD>
Mark Horton.
<EM>Portable C Software</EM>.
Prentice-Hall, 1990.
<P>
<DT><A NAME="kn:unix2"><STRONG>Int90</STRONG></A><DD>
Interviews.
Interview With Five Technologists.
<EM>UNIX Review</EM>, 8(1):41-89, January 1990.
<P>
<DT><A NAME="kn:fparith"><STRONG>KM86</STRONG></A><DD>
U. W. Kulish and W. L. Miranker.
The Arithmetic of the Digital Computer: A New Approach.
<EM>SIAM Review</EM>, 28(1):1-40, March 1986.
<P>
<DT><A NAME="kn:AK"><STRONG>Koe89</STRONG></A><DD>
Andrew Koenig.
<EM>C Traps and Pitfalls</EM>.
Addison-Wesley Publishing Co., Reading, Massachusetts, 1989.
<P>
<DT><A NAME="kn:KR"><STRONG>KR78</STRONG></A><DD>
Brian W. Kernighan and Dennis M. Ritchie.
<EM>The C Programming Language</EM>.
Prentice-Hall, Inc., 1978.
<P>
<DT><A NAME="kn:unix1"><STRONG>Man89</STRONG></A><DD>
Tom Manuel.
A Single Standard Emerges from the UNIX Tug-Of-War.
<EM>Electronics</EM>, pages 141-143, January 1989.
<P>
<DT><A NAME="kn:NRC"><STRONG>PFTV88</STRONG></A><DD>
William H. Press, Brian P. Flannery, Saul A. Teukolsky, and William T.
Vetterling.
<EM>NUMERICAL RECIPES in C: The Art of Scientific Computing</EM>.
Cambridge University Press, 1988.
<P>
<DT><A NAME="kn:ansi"><STRONG>X3J88</STRONG></A><DD>
X3J11.
Draft Proposed American National Standard for Information Systems
-- Programming Language C.
Technical Report X3J11/88-158, ANSI Accredited Standards
Committee, X3 Information Processing Systems, December 1988.
</DL>
<P>
<H1><A NAME="SECTION000170000000000000000"> About this document ... </A></H1>
<P>
<STRONG>Notes On Writing Portable Programs In C<BR>
(June 1990, 5th Revision)
</STRONG><P>
This document was generated using the <A HREF="http://www-dsed.llnl.gov/files/programs/unix/latex2html/manual/"><STRONG>LaTeX</STRONG>2<tt>HTML</tt></A> translator Version 96.1-h (September 30, 1996) Copyright © 1993, 1994, 1995, 1996, <A HREF="http://cbl.leeds.ac.uk/nikos/personal.html">Nikos Drakos</A>, Computer Based Learning Unit, University of Leeds. <P> The command line arguments were: <BR>
<STRONG>latex2html</STRONG> <tt>portableC.tex</tt>. <P>The translation was initiated by Christopher Lott on Thu Mar 13 13:33:05 EST 1997<DL> <DT><A NAME="6">...Lemmke</A><DD>Helsinki University of Technology,
Laboratory of Information Processing Sciences, SF-02150 Espoo, Finland.
This document is in the public domain.
Email address (Internet) are ado@sauna.hut.fi (preferred contact)
and arl@sauna.hut.fi, respectively.
<PRE>
</PRE><DT><A NAME="7">...Keppel</A><DD>CS&E, University of Washington. Email address (Internet) is
pardo@cs.washington.edu.
<PRE>
</PRE><DT><A NAME="326">...document</A><DD>It can be obtained via anonymous <EM>ftp</EM> from
<EM>cs.washington.edu</EM> in <EM>1#1ftp/pub/cstyle.tar.Z</EM>.
<PRE>
</PRE><DT><A NAME="19">...#kn:AK##1#]</A><DD>We note here that none of the information herein
as been taken from those two references.
<PRE>
</PRE><DT><A NAME="32">...programming</A><DD>We include raw I/O, e.g. from terminals in
this category.
<PRE>
</PRE><DT><A NAME="34">...document</A><DD>We regard
this document
as a living entity growing as needed and as information is gathered.
Future versions of this document may contain a lot of such information.
<PRE>
</PRE><DT><A NAME="328">...limits</A><DD>Maybe
there <B>are</B> people out there
who still write compilers in FORTRAN after all...
<PRE>
</PRE><DT><A NAME="330">...indented</EM></A><DD>Old preprocessors
only take directives which begin with <TT>#</TT> in the first column.
<PRE>
</PRE><DT><A NAME="331">...files</A><DD>Some have suggeested using <TT>#if __STDC__ ==
1</TT>
instead of simply <TT>#ifdef __STDC__</TT> to test if the compiler
is ANSI-compliant.
<PRE>
</PRE><DT><A NAME="332">...arguments</A><DD><TT>GLUE(a,GLUE(b,c))</TT> would not result in the concatenation
of <TT>a, b,</TT> and <TT>c</TT>.
<PRE>
</PRE><DT><A NAME="115">...Translation</EM></A><DD>Address
is 2051, Swans Neck Way, Reston, Virginia 22091, USA.
<PRE>
</PRE><DT><A NAME="122">...BSD</A><DD>Berkeley Software Distribution.
<PRE>
</PRE><DT><A NAME="335">...directory</A><DD>Under VMS,
since a path such as <TT><sys/file.h></TT> will evaluate to <TT>sys:file.h</TT>
it is sufficient to equate the logical name <TT>sys</TT> to <TT>sys$library</TT>.
<PRE>
</PRE><DT><A NAME="160">...VMS</A><DD>We are not sure this behaviour occurs only
under VMS.
<PRE>
</PRE><DT><A NAME="340">...handler</A><DD>That is, a function invoked
as a result of a signal raised during the handling of another signal.
See section 4.6.2.1 §15 in [<A HREF="portableC.html#kn:ansi">X3J88</A>].
<PRE>
</PRE><DT><A NAME="341">...statements</A><DD>Programs which generate other programs, e.g. YACC, can
generate, for instance, very large <B>switch</B> statements.
<PRE>
</PRE><DT><A NAME="188">...finite</A><DD>Some representations have reserved values
for +<I>inf</I> and -<I>inf</I>.
<PRE>
</PRE><DT><A NAME="342">...<EM>netlib</EM></A><DD>Email (Internet) address is netlib@ornl.gov.
For more information, send a message containing the line <EM>send index</EM>
to that address.
<PRE>
</PRE><DT><A NAME="343">...<B>comp.sources.misc</B></A><DD>The arquive site
of <B>comp.sources.misc</B> is <EM>uunet.uu.net</EM>.
<PRE>
</PRE><DT><A NAME="207">...</A><DD>In fact one wonders
why they even bothered to define two representations for floating-point numbers
considering the rules applied to them.
<PRE>
</PRE><DT><A NAME="253">...libraries</A><DD>This
does not really belong in this document but whenever one
is porting a program to a VMS environment one is bound to come across
this strange behaviour which can result in a lot of wasted time.
<PRE>
</PRE><DT><A NAME="347">...below</A><DD>The code will only
function correctly if <TT>sizeof(long int)</TT> is 32 bits. Although not
portable it serves well as an example for the given problem.
<PRE>
</PRE><DT><A NAME="283">...pointers</A><DD>One of the reasons for these rules is that in some
architectures pointers are represented as a pair of values and only
under those circumstances are two pairs comparable.
</DL>
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