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diff --git a/libstdc++-v3/doc/xml/manual/support.xml b/libstdc++-v3/doc/xml/manual/support.xml new file mode 100644 index 000000000..2cb7205bd --- /dev/null +++ b/libstdc++-v3/doc/xml/manual/support.xml @@ -0,0 +1,443 @@ +<chapter xmlns="http://docbook.org/ns/docbook" version="5.0" + xml:id="std.support" xreflabel="Support"> +<?dbhtml filename="support.html"?> + +<info><title> + Support + <indexterm><primary>Support</primary></indexterm> +</title> + <keywordset> + <keyword> + ISO C++ + </keyword> + <keyword> + library + </keyword> + </keywordset> +</info> + + <para> + This part deals with the functions called and objects created + automatically during the course of a program's existence. + </para> + + <para> + While we can't reproduce the contents of the Standard here (you + need to get your own copy from your nation's member body; see our + homepage for help), we can mention a couple of changes in what + kind of support a C++ program gets from the Standard Library. + </para> + +<section xml:id="std.support.types" xreflabel="Types"><info><title>Types</title></info> + <?dbhtml filename="fundamental_types.html"?> + + <section xml:id="std.support.types.fundamental" xreflabel="Fundamental Types"><info><title>Fundamental Types</title></info> + + <para> + C++ has the following builtin types: + </para> + <itemizedlist> + <listitem><para> + char + </para></listitem> + <listitem><para> + signed char + </para></listitem> + <listitem><para> + unsigned char + </para></listitem> + <listitem><para> + signed short + </para></listitem> + <listitem><para> + signed int + </para></listitem> + <listitem><para> + signed long + </para></listitem> + <listitem><para> + unsigned short + </para></listitem> + <listitem><para> + unsigned int + </para></listitem> + <listitem><para> + unsigned long + </para></listitem> + <listitem><para> + bool + </para></listitem> + <listitem><para> + wchar_t + </para></listitem> + <listitem><para> + float + </para></listitem> + <listitem><para> + double + </para></listitem> + <listitem><para> + long double + </para></listitem> + </itemizedlist> + + <para> + These fundamental types are always available, without having to + include a header file. These types are exactly the same in + either C++ or in C. + </para> + + <para> + Specializing parts of the library on these types is prohibited: + instead, use a POD. + </para> + + </section> + <section xml:id="std.support.types.numeric_limits" xreflabel="Numeric Properties"><info><title>Numeric Properties</title></info> + + + + <para> + The header <filename class="headerfile">limits</filename> defines + traits classes to give access to various implementation + defined-aspects of the fundamental types. The traits classes -- + fourteen in total -- are all specializations of the template class + <classname>numeric_limits</classname>, documented <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a00593.html">here</link> + and defined as follows: + </para> + + <programlisting> + template<typename T> + struct class + { + static const bool is_specialized; + static T max() throw(); + static T min() throw(); + + static const int digits; + static const int digits10; + static const bool is_signed; + static const bool is_integer; + static const bool is_exact; + static const int radix; + static T epsilon() throw(); + static T round_error() throw(); + + static const int min_exponent; + static const int min_exponent10; + static const int max_exponent; + static const int max_exponent10; + + static const bool has_infinity; + static const bool has_quiet_NaN; + static const bool has_signaling_NaN; + static const float_denorm_style has_denorm; + static const bool has_denorm_loss; + static T infinity() throw(); + static T quiet_NaN() throw(); + static T denorm_min() throw(); + + static const bool is_iec559; + static const bool is_bounded; + static const bool is_modulo; + + static const bool traps; + static const bool tinyness_before; + static const float_round_style round_style; + }; + </programlisting> + </section> + + <section xml:id="std.support.types.null" xreflabel="NULL"><info><title>NULL</title></info> + + <para> + The only change that might affect people is the type of + <constant>NULL</constant>: while it is required to be a macro, + the definition of that macro is <emphasis>not</emphasis> allowed + to be <constant>(void*)0</constant>, which is often used in C. + </para> + + <para> + For <command>g++</command>, <constant>NULL</constant> is + <code>#define</code>'d to be + <constant>__null</constant>, a magic keyword extension of + <command>g++</command>. + </para> + + <para> + The biggest problem of #defining <constant>NULL</constant> to be + something like <quote>0L</quote> is that the compiler will view + that as a long integer before it views it as a pointer, so + overloading won't do what you expect. (This is why + <command>g++</command> has a magic extension, so that + <constant>NULL</constant> is always a pointer.) + </para> + + <para>In his book <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.awprofessional.com/titles/0-201-92488-9/"><emphasis>Effective + C++</emphasis></link>, Scott Meyers points out that the best way + to solve this problem is to not overload on pointer-vs-integer + types to begin with. He also offers a way to make your own magic + <constant>NULL</constant> that will match pointers before it + matches integers. + </para> + <para>See + <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.awprofessional.com/titles/0-201-31015-5/">the + Effective C++ CD example</link> + </para> + </section> + +</section> + +<section xml:id="std.support.memory" xreflabel="Dynamic Memory"><info><title>Dynamic Memory</title></info> + <?dbhtml filename="dynamic_memory.html"?> + + <para> + There are six flavors each of <function>new</function> and + <function>delete</function>, so make certain that you're using the right + ones. Here are quickie descriptions of <function>new</function>: + </para> + <itemizedlist> + <listitem><para> + single object form, throwing a + <classname>bad_alloc</classname> on errors; this is what most + people are used to using + </para></listitem> + <listitem><para> + Single object "nothrow" form, returning NULL on errors + </para></listitem> + <listitem><para> + Array <function>new</function>, throwing + <classname>bad_alloc</classname> on errors + </para></listitem> + <listitem><para> + Array nothrow <function>new</function>, returning + <constant>NULL</constant> on errors + </para></listitem> + <listitem><para> + Placement <function>new</function>, which does nothing (like + it's supposed to) + </para></listitem> + <listitem><para> + Placement array <function>new</function>, which also does + nothing + </para></listitem> + </itemizedlist> + <para> + They are distinguished by the parameters that you pass to them, like + any other overloaded function. The six flavors of <function>delete</function> + are distinguished the same way, but none of them are allowed to throw + an exception under any circumstances anyhow. (They match up for + completeness' sake.) + </para> + <para> + Remember that it is perfectly okay to call <function>delete</function> on a + NULL pointer! Nothing happens, by definition. That is not the + same thing as deleting a pointer twice. + </para> + <para> + By default, if one of the <quote>throwing <function>new</function>s</quote> can't + allocate the memory requested, it tosses an instance of a + <classname>bad_alloc</classname> exception (or, technically, some class derived + from it). You can change this by writing your own function (called a + new-handler) and then registering it with <function>set_new_handler()</function>: + </para> + <programlisting> + typedef void (*PFV)(void); + + static char* safety; + static PFV old_handler; + + void my_new_handler () + { + delete[] safety; + popup_window ("Dude, you are running low on heap memory. You + should, like, close some windows, or something. + The next time you run out, we're gonna burn!"); + set_new_handler (old_handler); + return; + } + + int main () + { + safety = new char[500000]; + old_handler = set_new_handler (&my_new_handler); + ... + } + </programlisting> + <para> + <classname>bad_alloc</classname> is derived from the base <classname>exception</classname> + class defined in Sect1 19. + </para> +</section> + +<section xml:id="std.support.termination" xreflabel="Termination"><info><title>Termination</title></info> + <?dbhtml filename="termination.html"?> + + <section xml:id="support.termination.handlers" xreflabel="Termination Handlers"><info><title>Termination Handlers</title></info> + + <para> + Not many changes here to <filename class="headerfile">cstdlib</filename>. You should note that the + <function>abort()</function> function does not call the + destructors of automatic nor static objects, so if you're + depending on those to do cleanup, it isn't going to happen. + (The functions registered with <function>atexit()</function> + don't get called either, so you can forget about that + possibility, too.) + </para> + <para> + The good old <function>exit()</function> function can be a bit + funky, too, until you look closer. Basically, three points to + remember are: + </para> + <orderedlist inheritnum="ignore" continuation="restarts"> + <listitem> + <para> + Static objects are destroyed in reverse order of their creation. + </para> + </listitem> + <listitem> + <para> + Functions registered with <function>atexit()</function> are called in + reverse order of registration, once per registration call. + (This isn't actually new.) + </para> + </listitem> + <listitem> + <para> + The previous two actions are <quote>interleaved,</quote> that is, + given this pseudocode: + </para> +<programlisting> + extern "C or C++" void f1 (void); + extern "C or C++" void f2 (void); + + static Thing obj1; + atexit(f1); + static Thing obj2; + atexit(f2); +</programlisting> + <para> + then at a call of <function>exit()</function>, + <varname>f2</varname> will be called, then + <varname>obj2</varname> will be destroyed, then + <varname>f1</varname> will be called, and finally + <varname>obj1</varname> will be destroyed. If + <varname>f1</varname> or <varname>f2</varname> allow an + exception to propagate out of them, Bad Things happen. + </para> + </listitem> + </orderedlist> + <para> + Note also that <function>atexit()</function> is only required to store 32 + functions, and the compiler/library might already be using some of + those slots. If you think you may run out, we recommend using + the <function>xatexit</function>/<function>xexit</function> combination from <literal>libiberty</literal>, which has no such limit. + </para> + </section> + + <section xml:id="support.termination.verbose" xreflabel="Verbose Terminate Handler"><info><title>Verbose Terminate Handler</title></info> + <?dbhtml filename="verbose_termination.html"?> + + <para> + If you are having difficulty with uncaught exceptions and want a + little bit of help debugging the causes of the core dumps, you can + make use of a GNU extension, the verbose terminate handler. + </para> + +<programlisting> +#include <exception> + +int main() +{ + std::set_terminate(__gnu_cxx::__verbose_terminate_handler); + ... + + throw <replaceable>anything</replaceable>; +} +</programlisting> + + <para> + The <function>__verbose_terminate_handler</function> function + obtains the name of the current exception, attempts to demangle + it, and prints it to stderr. If the exception is derived from + <classname>exception</classname> then the output from + <function>what()</function> will be included. + </para> + + <para> + Any replacement termination function is required to kill the + program without returning; this one calls abort. + </para> + + <para> + For example: + </para> + +<programlisting> +#include <exception> +#include <stdexcept> + +struct argument_error : public std::runtime_error +{ + argument_error(const std::string& s): std::runtime_error(s) { } +}; + +int main(int argc) +{ + std::set_terminate(__gnu_cxx::__verbose_terminate_handler); + if (argc > 5) + throw argument_error(<quote>argc is greater than 5!</quote>); + else + throw argc; +} +</programlisting> + + <para> + With the verbose terminate handler active, this gives: + </para> + + <screen> + <computeroutput> + % ./a.out + terminate called after throwing a `int' + Aborted + % ./a.out f f f f f f f f f f f + terminate called after throwing an instance of `argument_error' + what(): argc is greater than 5! + Aborted + </computeroutput> + </screen> + + <para> + The 'Aborted' line comes from the call to + <function>abort()</function>, of course. + </para> + + <para> + This is the default termination handler; nothing need be done to + use it. To go back to the previous <quote>silent death</quote> + method, simply include <filename>exception</filename> and + <filename>cstdlib</filename>, and call + </para> + + <programlisting> + std::set_terminate(std::abort); + </programlisting> + + <para> + After this, all calls to <function>terminate</function> will use + <function>abort</function> as the terminate handler. + </para> + + <para> + Note: the verbose terminate handler will attempt to write to + stderr. If your application closes stderr or redirects it to an + inappropriate location, + <function>__verbose_terminate_handler</function> will behave in + an unspecified manner. + </para> + + </section> +</section> + +</chapter> |