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C++ Producer Guide: Standard library
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</HEAD>
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<BODY TEXT="#000000" BGCOLOR="#FFFFFF" LINK="#0000FF" VLINK="#400080" ALINK="#FF0000">
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<H1>C++ Producer Guide</H1>
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<H3>March 1998</H3>
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<A HREF="style.html"><IMG SRC="../images/next.gif" ALT="next section"></A>
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<A HREF="lib.html"><IMG SRC="../images/prev.gif" ALT="previous section"></A>
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<A HREF="index.html"><IMG SRC="../images/top.gif" ALT="current document"></A>
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<A HREF="../index.html"><IMG SRC="../images/home.gif" ALT="TenDRA home page">
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</A>
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<IMG SRC="../images/no_index.gif" ALT="document index"><P>
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<HR>
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<DL>
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<DT><A HREF="#porting"><B>2.7.1</B> - Common porting problems</A><DD>
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<DT><A HREF="#libio"><B>2.7.2</B> - Porting <CODE>libio</CODE></A><DD>
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</DL>
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<HR>
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<H2>2.7. Standard library</H2>
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<P>
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At present the default implementation contains only a very small fraction
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of the ISO C++ library, namely those headers -
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<CODE><exception></CODE>, <CODE><new></CODE> and
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<CODE><typeinfo></CODE> - which are an integral part of the
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language specification. These headers are also those which require
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the most cooperation between the producer and the library implementation,
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as described in the <A HREF="lib.html">previous section</A>.
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</P>
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<P>
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It is suggested that if further library components are required then
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they be acquired from third parties. It should be noted however that
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such libraries may require <A HREF="#porting">some effort</A> to be
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ported to an ISO compliant compiler; for example, some information
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on porting the <CODE>libio</CODE> component of <CODE>libg++</CODE>,
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which contains some very compiler-dependent code, are
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<A HREF="#libio">given below</A>. Libraries compiled with other C++
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compilers may not link correctly with modules compiled using <CODE>tcc</CODE>.
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</P>
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<HR>
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<H3><A NAME="porting">2.7.1. Common porting problems</A></H3>
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<P>
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Experience in porting pre-ISO C++ programs has shown that the following
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new ISO C++ features tend to cause the most problems:
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<OL>
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<LI><A HREF="pragma.html#implicit">Implicit <CODE>int</CODE></A> has
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been banned.
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<LI><A HREF="pragma.html#string">String literals are now <CODE>const</CODE>
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</A>, although in simple assignments the <CODE>const</CODE> is
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implicitly removed.
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<LI>The scope of a <A HREF="pragma.html#for">variable declared in
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a for-init-statement</A> is the <CODE>for</CODE> statement itself.
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<LI><A HREF="lib.html#mangle">Variables have linkage</A> and so should
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be declared <CODE>extern "C"</CODE> if appropriate.
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<LI>The standard C library is now declared in the <CODE>std</CODE>
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namespace.
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<LI>The <A HREF="pragma.html#template">template compilation model</A>
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has been clarified. The notation for explicit instantiation and
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specialisation has changed.
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<LI>Templates are analysed at their point of definition as well as
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their point of instantiation.
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<LI><A HREF="pragma.html#keyword">New keywords</A> have been introduced.
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</OL>
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Note that many of these features have controlling <CODE>#pragma</CODE>
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directives, so that it is possible to switch to using the pre-ISO
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features.
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</P>
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<HR>
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<H3><A NAME="libio">2.7.2. Porting <CODE>libio</CODE></A></H3>
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<P>
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Perhaps the library component which is most likely to be required
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is
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<CODE><iostream></CODE>. A readily available freeware implementation
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of a pre-ISO (i.e. non-template) <CODE><iostream></CODE>
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package is given by the <CODE>libio</CODE> component of <CODE>libg++</CODE>.
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This section describes some of the problems encountered in porting
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this package (version 2.7.1).
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</P>
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<P>
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The <A HREF="man.html"><CODE>tcc</CODE> compiler flags</A> used in
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porting <CODE>libio</CODE> were:
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<PRE>
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tcc -Yposix -Yc++ -sC:cc
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</PRE>
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indicating that the POSIX API is to be used and that the <CODE>.cc</CODE>
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suffix is used to identify C++ source files.
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</P>
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<P>
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In <CODE>iostream.h</CODE>, <CODE>cin</CODE>, <CODE>cout</CODE>,
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<CODE>cerr</CODE> and <CODE>clog</CODE> should be declared with C
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linkage, otherwise the C++ producer includes the type in the
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<A HREF="lib.html#mangle">mangled name</A> and the fake
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<CODE>iostream</CODE> hacks in <CODE>stdstream.cc</CODE> don't work.
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The definition of <CODE>EOF</CODE> in this header can cause problems
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if both <CODE>iostream.h</CODE> and <CODE>stdio.h</CODE> are included.
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In this case <CODE>stdio.h</CODE> should be included first.
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</P>
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<P>
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In <CODE>stdstream.cc</CODE>, the <A HREF="lib.html#derive">correct
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definitions</A> for the fake <CODE>iostream</CODE> structures are
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as follows:
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<PRE>
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struct _fake_istream::myfields {
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_ios_fields *vb ; // pointer to virtual base class ios
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_IO_ssize_t _gcount ; // istream fields
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void *vptr ; // pointer to virtual function table
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} ;
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struct _fake_ostream::myfields {
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_ios_fields *vb ; // pointer to virtual base class ios
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void *vptr ; // pointer to virtual function table
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} ;
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</PRE>
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The fake definition macros are then defined as follows:
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<PRE>
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#define OSTREAM_DEF( NAME, SBUF, TIE, EXTRA_FLAGS )\
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extern "C" _fake_ostream NAME = { { &NAME.base, 0 }, .... } ;
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#define ISTREAM_DEF( NAME, SBUF, TIE, EXTRA_FLAGS )\
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extern "C" _fake_istream NAME = { { &NAME.base, 0, 0 }, .... } ;
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</PRE>
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Note that these are declared with C linkage as above.
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</P>
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<P>
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In <CODE>stdstrbufs.cc</CODE>, the <A HREF="lib.html#other">correct
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definitions</A> for the virtual function table names are as follows:
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<PRE>
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#define filebuf_vtable __vt__7filebuf
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#define stdiobuf_vtable __vt__8stdiobuf
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</PRE>
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Note that the <CODE>_G_VTABLE_LABEL_PREFIX</CODE> macro is incorrectly
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defined by the configuration process (it should be <CODE>__vt__</CODE>),
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but the <CODE>##</CODE> directives in which it is used don't work
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on an ISO compliant preprocessor anyway (token concatenation takes
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place after replacement of macro parameters, but before further macro
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expansion). The dummy virtual function tables should also be declared
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with C linkage to suppress name mangling.
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</P>
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In addition, the initialisation of the standard streams relies on
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the file pointers <CODE>stdout</CODE> etc. being constant expressions,
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which in general they are not. The directive:
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<PRE>
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#pragma TenDRA++ rvalue token as const allow
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</PRE>
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will cause the C++ producer to assume that all <A HREF="token.html#exp">
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tokenised rvalue expressions</A> are constant.
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<P>
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In <CODE>streambuf.cc</CODE>, if <CODE>errno</CODE> is to be explicitly
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declared it should have C linkage or be declared in the <CODE>std</CODE>
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namespace.
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</P>
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<P>
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In <CODE>iomanip.cc</CODE>, the explicit template instantiations should
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be prefixed by <CODE>template</CODE>. The corresponding template
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declarations in <CODE>iomanip.h</CODE> should be declared using
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<A HREF="pragma.html#template"><CODE>export</CODE></A> (note that
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the <CODE>__GNUG__</CODE> version uses <CODE>extern</CODE>, which
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may yet win out over <CODE>export</CODE>).
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</P>
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<HR>
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<P><I>Part of the <A HREF="../index.html">TenDRA Web</A>.<BR>Crown
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Copyright © 1998.</I></P>
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</BODY>
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</HTML>
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