From: daniel_james_at_[hidden]
Date: 2007-11-04 14:09:57
Author: danieljames
Date: 2007-11-04 14:09:56 EST (Sun, 04 Nov 2007)
New Revision: 40751
URL: http://svn.boost.org/trac/boost/changeset/40751
Log:
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Removed:
trunk/more/borland_cpp.html
Deleted: trunk/more/borland_cpp.html
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-<html>
-<head>
- <meta http-equiv="Content-Language" content="en-us">
- <meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
-
- <title>Portability Hints: Borland C++ 5.5.1</title>
-</head>
-
-<body bgcolor="#FFFFFF" text="#000000">
- <table border="1" bgcolor="#007F7F" cellpadding="2" summary="">
- <tr>
- <td bgcolor="#FFFFFF"><img src="../boost.png" alt=
- "boost.png (6897 bytes)" width="277" height="86"></td>
-
- <td><a href="../index.htm"><font face="Arial,Helvetica" color=
- "#FFFFFF"><big>Home</big></font></a></td>
-
- <td><a href="../libs/libraries.htm"><font face="Arial,Helvetica" color=
- "#FFFFFF"><big>Libraries</big></font></a></td>
-
- <td><a href="../people/people.htm"><font face="Arial,Helvetica" color=
- "#FFFFFF"><big>People</big></font></a></td>
-
- <td><a href="faq.htm"><font face="Arial,Helvetica" color=
- "#FFFFFF"><big>FAQ</big></font></a></td>
-
- <td><a href="index.htm"><font face="Arial,Helvetica" color=
- "#FFFFFF"><big>More</big></font></a></td>
- </tr>
- </table>
-
- <h1>Portability Hints: Borland C++ 5.5.1</h1>
-
- <p>It is a general aim for boost libraries to be <a href=
- "lib_guide.htm#Portability">portable</a>. The primary means for achieving
- this goal is to adhere to ISO Standard C++. However, ISO C++ is a broad and
- complex standard and most compilers are not fully conformant to ISO C++
- yet. In order to achieve portability in the light of this restriction, it
- seems advisable to get acquainted with those language features that some
- compilers do not fully implement yet.</p>
-
- <p>This page gives portability hints on some language features of the
- Borland C++ version 5.5.1 compiler. Furthermore, the appendix presents
- additional problems with Borland C++ version 5.5. Borland C++ 5.5.1 is a
- freely available command-line compiler for Win32 available at <a href=
- "http://www.borland.com/">http://www.borland.com/>.</p>
-
- <p>Each entry in the following list describes a particular issue, complete
- with sample source code to demonstrate the effect. Most sample code herein
- has been verified to compile with gcc 2.95.2 and Comeau C++ 4.2.44.</p>
-
- <h2>Preprocessor symbol</h2>
-
- <p>The preprocessor symbol <code>__BORLANDC__</code> is defined for all
- Borland C++ compilers. Its value is the version number of the compiler
- interpreted as a hexadecimal number. The following table lists some known
- values.</p>
-
- <table border="1" summary="">
- <tr>
- <th>Compiler</th>
-
- <th><code>__BORLANDC__</code> value</th>
- </tr>
-
- <tr>
- <td>Borland C++ Builder 4</td>
-
- <td>0x0540</td>
- </tr>
-
- <tr>
- <td>Borland C++ Builder 5</td>
-
- <td>0x0550</td>
- </tr>
-
- <tr>
- <td>Borland C++ 5.5</td>
-
- <td>0x0550</td>
- </tr>
-
- <tr>
- <td>Borland C++ 5.5.1</td>
-
- <td>0x0551</td>
- </tr>
-
- <tr>
- <td>Borland C++ Builder 6</td>
-
- <td>0x0560</td>
- </tr>
- </table>
-
- <h2>Core Language</h2>
-
- <h3>[using-directive] Mixing <code>using</code>-declarations and
- <code>using</code>-directives</h3>
-
- <p>Mixing <code>using</code>-directives (which refer to whole namespaces)
- and namespace-level <code>using</code>-declarations (which refer to
- individual identifiers within foreign namespaces) causes ambiguities where
- there are none. The following code fragment illustrates this:</p>
- <pre>
-namespace N {
- int x();
-}
-
-using N::x;
-using namespace N;
-
-int main()
-{
- &x; // Ambiguous overload
-}
-</pre>
-
- <h3>[using template] <code>using</code>-declarations for class
- templates</h3>
-
- <p>Identifiers for class templates can be used as arguments to
- <code>using</code>-declarations as any other identifier. However, the
- following code fails to compile with Borland C++:</p>
- <pre>
-template<class T>
-class X { };
-
-namespace N
-{
- // "cannot use template 'X<T>' without specifying specialization parameters"
- using ::X;
-};
-</pre>
-
- <h3>[template const arg] Deduction of constant arguments to function
- templates</h3>
-
- <p>Template function type deduction should omit top-level constness.
- However, this code fragment instantiates "f<const int>(int)":</p>
- <pre>
-template<class T>
-void f(T x)
-{
- x = 1; // works
- (void) &x;
- T y = 17;
- y = 20; // "Cannot modify a const object in function f<const int>(int)"
- (void) &y;
-}
-
-int main()
-{
- const int i = 17;
- f(i);
-}
-</pre>
-
- <h3>[function address] Resolving addresses of overloaded functions</h3>
-
- <p>Addresses of overloaded functions are not in all contexts properly
- resolved (std:13.4 [over.over]); here is a small example:</p>
- <pre>
-template<class Arg>
-void f( void(*g)(Arg) );
-
-void h(int);
-void h(double);
-
-template<class T>
-void h2(T);
-
-int main()
-{
- void (*p)(int) = h; // this works (std:13.4-1.1)
- void (*p2)(unsigned char) = h2; // this works as well (std:13.4-1.1)
- f<int>(h2); // this also works (std:13.4-1.3)
-
- // "Cannot generate template specialization from h(int)",
- // "Could not find a match for f<Arg>(void (*)(int))"
- f<double>(h); // should work (std:13.4-1.3)
-
- f( (void(*)(double))h); // C-style cast works (std:13.4-1.6 with 5.4)
-
- // "Overloaded 'h' ambiguous in this context"
- f(static_cast<void(*)(double)>(h)); // should work (std:13.4-1.6 with 5.2.9)
-}
-</pre>
-
- <p><strong>Workaround:</strong> Always use C-style casts when determining
- addresses of (potentially) overloaded functions.</p>
-
- <h3>[string conversion] Converting <code>const char *</code> to
- <code>std::string</code></h3>
-
- <p>Implicitly converting <code>const char *</code> parameters to
- <code>std::string</code> arguments fails if template functions are
- explicitly instantiated (it works in the usual cases, though):</p>
- <pre>
-#include <string>
-
-template<class T>
-void f(const std::string & s)
-{}
-
-int main()
-{
- f<double>("hello"); // "Could not find a match for f<T>(char *)"
-}
-
-</pre>
-
- <p><strong>Workaround:</strong> Avoid explicit template function
- instantiations (they have significant problems with Microsoft Visual C++)
- and pass default-constructed unused dummy arguments with the appropriate
- type. Alternatively, if you wish to keep to the explicit instantiation, you
- could use an explicit conversion to <code>std::string</code> or declare the
- template function as taking a <code>const char *</code> parameter.</p>
-
- <h3>[template value defaults] Dependent default arguments for template
- value parameters</h3>
-
- <p>Template value parameters which default to an expression dependent on
- previous template parameters don't work:</p>
- <pre>
-template<class T>
-struct A
-{
- static const bool value = true;
-};
-
-// "Templates must be classes or functions", "Declaration syntax error"
-template<class T, bool v = A<T>::value>
-struct B {};
-
-int main()
-{
- B<int> x;
-}
-
-</pre>
-
- <p><strong>Workaround:</strong> If the relevant non-type template parameter
- is an implementation detail, use inheritance and a fully qualified
- identifier (for example, ::N::A<T>::value).</p>
-
- <h3>[function partial ordering] Partial ordering of function templates</h3>
-
- <p>Partial ordering of function templates, as described in std:14.5.5.2
- [temp.func.order], does not work:</p>
- <pre>
-#include <iostream>
-
-template<class T> struct A {};
-
-template<class T1>
-void f(const A<T1> &)
-{
- std::cout << "f(const A<T1>&)\n";
-}
-
-template<class T>
-void f(T)
-{
- std::cout << "f(T)\n";
-}
-
-int main()
-{
- A<double> a;
- f(a); // output: f(T) (wrong)
- f(1); // output: f(T) (correct)
-}
-</pre>
-
- <p><strong>Workaround:</strong> Declare all such functions uniformly as
- either taking a value or a reference parameter.</p>
-
- <h3>[instantiate memfun ptr] Instantiation with member function
- pointer</h3>
-
- <p>When directly instantiating a template with some member function
- pointer, which is itself dependent on some template parameter, the compiler
- cannot cope:</p>
- <pre>
-template<class U> class C { };
-template<class T>
-class A
-{
- static const int v = C<void (T::*)()>::value;
-};
-</pre>
-
- <p><strong>Workaround:</strong> Use an intermediate
- <code>typedef</code>:</p>
- <pre>
-template<class U> class C { };
-template<class T>
-class A
-{
- typedef void (T::*my_type)();
- static const int v = C<my_type>::value;
-};
-</pre>
-
- <p>(Extracted from e-mail exchange of David Abrahams, Fernando Cacciola,
- and Peter Dimov; not actually tested.)</p>
-
- <h2>Library</h2>
-
- <h3>[cmath.abs] Function <code>double std::abs(double)</code> missing</h3>
-
- <p>The function <code>double std::abs(double)</code> should be defined
- (std:26.5-5 [lib.c.math]), but it is not:</p>
- <pre>
-#include <cmath>
-
-int main()
-{
- double (*p)(double) = std::abs; // error
-}
-</pre>
-
- <p>Note that <code>int std::abs(int)</code> will be used without warning if
- you write <code>std::abs(5.1)</code>.</p>
-
- <p>Similar remarks apply to seemingly all of the other standard math
- functions, where Borland C++ fails to provide <code>float</code> and
- <code>long double</code> overloads.</p>
-
- <p><strong>Workaround:</strong> Use <code>std::fabs</code> instead if type
- genericity is not required.</p>
-
- <h2>Appendix: Additional issues with Borland C++ version 5.5</h2>
-
- <p>These issues are documented mainly for historic reasons. If you are
- still using Borland C++ version 5.5, you are strongly encouraged to obtain
- an upgrade to version 5.5.1, which fixes the issues described in this
- section.</p>
-
- <h3>[inline friend] Inline friend functions in template classes</h3>
-
- <p>If a friend function of some class has not been declared before the
- friend function declaration, the function is declared at the namespace
- scope surrounding the class definition. Together with class templates and
- inline definitions of friend functions, the code in the following fragment
- should declare (and define) a non-template function "bool N::f(int,int)",
- which is a friend of class N::A<int>. However, Borland C++ v5.5
- expects the function f to be declared beforehand:</p>
- <pre>
-namespace N {
-template<class T>
-class A
-{
- // "f is not a member of 'N' in function main()"
- friend bool f(T x, T y) { return x < y; }
-};
-}
-
-int main()
-{
- N::A<int> a;
-}
-</pre>
-
- <p>This technique is extensively used in boost/operators.hpp. Giving in to
- the wish of the compiler doesn't work in this case, because then the
- "instantiate one template, get lots of helper functions at namespace scope"
- approach doesn't work anymore. Defining BOOST_NO_OPERATORS_IN_NAMESPACE (a
- define BOOST_NO_INLINE_FRIENDS_IN_CLASS_TEMPLATES would match this case
- better) works around this problem and leads to another one, see
- [using-template].</p>
- <hr>
-
- <p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src=
- "http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Transitional"
- height="31" width="88"></a></p>
-
- <p>Revised
- <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->03
- December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38512" --></p>
-
- <p><i>Copyright © 2000-2002 <a href="../people/jens_maurer.htm">Jens
- Maurer</a></i></p>
-
- <p><i>Distributed under the Boost Software License, Version 1.0. (See
- accompanying file LICENSE_1_0.txt or copy
- at <a href=
- "http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt>)</i></p>
-</body>
-</html>