| <chapter xmlns="http://docbook.org/ns/docbook" version="5.0" |
| xml:id="std.diagnostics" xreflabel="Diagnostics"> |
| <?dbhtml filename="diagnostics.html"?> |
| |
| <info><title> |
| Diagnostics |
| <indexterm><primary>Diagnostics</primary></indexterm> |
| </title> |
| <keywordset> |
| <keyword>ISO C++</keyword> |
| <keyword>library</keyword> |
| </keywordset> |
| </info> |
| |
| |
| |
| <section xml:id="std.diagnostics.exceptions" xreflabel="Exceptions"><info><title>Exceptions</title></info> |
| <?dbhtml filename="exceptions.html"?> |
| |
| |
| <section xml:id="std.diagnostics.exceptions.api"><info><title>API Reference</title></info> |
| |
| <para> |
| All exception objects are defined in one of the standard header |
| files: <filename>exception</filename>, |
| <filename>stdexcept</filename>, <filename>new</filename>, and |
| <filename>typeinfo</filename>. |
| </para> |
| |
| <para> |
| The base exception object is <classname>exception</classname>, |
| located in <filename>exception</filename>. This object has no |
| <classname>string</classname> member. |
| </para> |
| |
| <para> |
| Derived from this are several classes that may have a |
| <classname>string</classname> member: a full hierarchy can be |
| found in the source documentation. |
| </para> |
| |
| <para> |
| Full API details. |
| </para> |
| |
| <!-- Doxygen XML: api/group__exceptions.xml --> |
| |
| </section> |
| <section xml:id="std.diagnostics.exceptions.data" xreflabel="Adding Data to Exceptions"><info><title>Adding Data to <classname>exception</classname></title></info> |
| |
| <para> |
| The standard exception classes carry with them a single string as |
| data (usually describing what went wrong or where the 'throw' took |
| place). It's good to remember that you can add your own data to |
| these exceptions when extending the hierarchy: |
| </para> |
| <programlisting> |
| struct My_Exception : public std::runtime_error |
| { |
| public: |
| My_Exception (const string& whatarg) |
| : std::runtime_error(whatarg), e(errno), id(GetDataBaseID()) { } |
| int errno_at_time_of_throw() const { return e; } |
| DBID id_of_thing_that_threw() const { return id; } |
| protected: |
| int e; |
| DBID id; // some user-defined type |
| }; |
| </programlisting> |
| |
| </section> |
| </section> |
| |
| <section xml:id="std.diagnostics.concept_checking" xreflabel="Concept Checking"><info><title>Concept Checking</title></info> |
| <?dbhtml filename="concept_checking.html"?> |
| |
| <para> |
| In 1999, SGI added <quote>concept checkers</quote> to their |
| implementation of the STL: code which checked the template |
| parameters of instantiated pieces of the STL, in order to insure |
| that the parameters being used met the requirements of the |
| standard. For example, the Standard requires that types passed as |
| template parameters to <classname>vector</classname> be |
| "Assignable" (which means what you think it means). The |
| checking was done during compilation, and none of the code was |
| executed at runtime. |
| </para> |
| <para> |
| Unfortunately, the size of the compiler files grew significantly |
| as a result. The checking code itself was cumbersome. And bugs |
| were found in it on more than one occasion. |
| </para> |
| <para> |
| The primary author of the checking code, Jeremy Siek, had already |
| started work on a replacement implementation. The new code was |
| formally reviewed and accepted into |
| <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.boost.org/libs/concept_check/concept_check.htm">the |
| Boost libraries</link>, and we are pleased to incorporate it into the |
| GNU C++ library. |
| </para> |
| <para> |
| The new version imposes a much smaller space overhead on the generated |
| object file. The checks are also cleaner and easier to read and |
| understand. |
| </para> |
| |
| <para> |
| They are off by default for all versions of GCC. |
| They can be enabled at configure time with |
| <link linkend="manual.intro.setup.configure"><literal>--enable-concept-checks</literal></link>. |
| You can enable them on a per-translation-unit basis with |
| <literal>-D_GLIBCXX_CONCEPT_CHECKS</literal>. |
| </para> |
| |
| <para> |
| Please note that the checks are based on the requirements in the original |
| C++ standard, some of which have changed in the new C++11 revision. |
| Additionally, some correct code might be rejected by the concept checks, |
| for example template argument types may need to be complete when used in |
| a template definition, rather than at the point of instantiation. |
| There are no plans to address these shortcomings. |
| </para> |
| |
| </section> |
| |
| </chapter> |