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| |
| <part id="manual.diagnostics" xreflabel="Diagnostics"> |
| <?dbhtml filename="diagnostics.html"?> |
| |
| <partinfo> |
| <keywordset> |
| <keyword> |
| ISO C++ |
| </keyword> |
| <keyword> |
| library |
| </keyword> |
| </keywordset> |
| </partinfo> |
| |
| <title> |
| Diagnostics |
| <indexterm><primary>Diagnostics</primary></indexterm> |
| </title> |
| |
| <chapter id="manual.diagnostics.exceptions" xreflabel="Exceptions"> |
| <?dbhtml filename="exceptions.html"?> |
| <title>Exceptions</title> |
| |
| <sect1 id="manual.diagnostics.exceptions.hierarchy" xreflabel="Exception Classes"> |
| <title>Exception Classes</title> |
| <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 <ulink url="http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/a00233.html">source documentation</ulink>. |
| </para> |
| |
| </sect1> |
| <sect1 id="manual.diagnostics.exceptions.data" xreflabel="Adding Data to Exceptions"> |
| <title>Adding Data to Exceptions</title> |
| <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> |
| |
| </sect1> |
| <sect1 id="manual.diagnostics.exceptions.cancellation" xreflabel="Cancellation"> |
| <title>Cancellation</title> |
| <para> |
| </para> |
| </sect1> |
| </chapter> |
| |
| <chapter id="manual.diagnostics.concept_checking" xreflabel="Concept Checking"> |
| <title>Concept Checking</title> |
| <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 has been |
| formally reviewed and accepted into |
| <ulink url="http://www.boost.org/libs/concept_check/concept_check.htm">the |
| Boost libraries</ulink>, 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 |
| <ulink url="../configopts.html"><literal>--enable-concept-checks</literal></ulink>. |
| You can enable them on a per-translation-unit basis with |
| <literal>-D_GLIBCXX_CONCEPT_CHECKS</literal>. |
| </para> |
| |
| <para> |
| Please note that the upcoming C++ standard has first-class |
| support for template parameter constraints based on concepts in the core |
| language. This will obviate the need for the library-simulated concept |
| checking described above. |
| </para> |
| |
| </chapter> |
| |
| </part> |