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* Attempt to solve issue #10 In boost::current_exception(), after all supported types of exception have been checked for, a boost::unknown_exception is stored in the boost::exception_ptr as a last resort to signal that an exception was indeed stored, but that the actual type and value of the exception was lost. Now, in case C++11 std::current_exception() is supported, the std::exception_ptr result of calling std::current_exception() is what gets stored inside the boost::exception_ptr. Later, inside boost::rethrow_exception, the std::exception_ptr is retrieved from the boost::exception_ptr and whatever exception it stores is thrown via std::rethrow_exception(). The main benefit is than now any exception thrown via plain 'throw' can be trasnported via boost::exception_ptr. Before this change it was required that the throw site either used boost::enable_current_exception() or boost::throw_exception() or threw an exception type inheriting from boost::exception, which was impossible for third party software that does not use Boost.Exception. The detection of std::current_exception() is currently done via config macro BOOST_NO_CXX11_NOEXCEPT, assuming that if 'noexcept' is supported then std::exception_ptr is also supported. A better solution would require a new dedicated macro in Boost.Config. * Detect support for std::current_exception() via config macro BOOST_NO_CXX11_HDR_EXCEPTION The temporary solution via BOOST_NO_CXX11_NOEXCEPT was an ugly hack that is no longer necessary now that Boost.Config has BOOST_NO_CXX11_HDR_EXCEPTION (pending merge to develop). * Attempt to solve issue #10 In boost::current_exception(), after all supported types of exception have been checked for, a boost::unknown_exception is stored in the boost::exception_ptr as a last resort to signal that an exception was indeed stored, but that the actual type and value of the exception was lost. Now, in case C++11 std::current_exception() is supported, the std::exception_ptr result of calling std::current_exception() is what gets stored inside the boost::exception_ptr. Later, inside boost::rethrow_exception, the std::exception_ptr is retrieved from the boost::exception_ptr and whatever exception it stores is thrown via std::rethrow_exception(). The main benefit is than now any exception thrown via plain 'throw' can be trasnported via boost::exception_ptr. Before this change it was required that the throw site either used boost::enable_current_exception() or boost::throw_exception() or threw an exception type inheriting from boost::exception, which was impossible for third party software that does not use Boost.Exception. The detection of std::current_exception() is currently done via config macro BOOST_NO_CXX11_NOEXCEPT, assuming that if 'noexcept' is supported then std::exception_ptr is also supported. A better solution would require a new dedicated macro in Boost.Config. * Detect support for std::current_exception() via config macro BOOST_NO_CXX11_HDR_EXCEPTION The temporary solution via BOOST_NO_CXX11_NOEXCEPT was an ugly hack that is no longer necessary now that Boost.Config has BOOST_NO_CXX11_HDR_EXCEPTION (pending merge to develop). * Document detection of C++11 std::current_exception through BOOST_NO_CXX11_HDR_EXCEPTION * Added dist: trusty for Travis config, as recommended by pdimov in issue #10 * Stupid gcc 4.7 and 4.8 are confused initializing a reference with braces, using equal sign hoping it works (tested similar code on godbolt).
65 lines
5.7 KiB
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65 lines
5.7 KiB
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<title>current_exception</title>
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<a href="http://www.boost.org"><img style="border:0" src="../../../boost.png" alt="Boost" width="277" height="86"/></a>
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<h1>Boost Exception</h1>
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<!-- Copyright (c) 2006-2009 Emil Dotchevski and Reverge Studios, Inc. -->
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<!-- Distributed under the Boost Software License, Version 1.0. (See accompanying -->
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<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
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<div class="RenoIncludeDIV"><div class="RenoAutoDIV"><h3>current_exception</h3>
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<div class="RenoIncludeDIV"><p><span class="RenoEscape">#<!--<wiki>`#</wiki>--></span>include <<span class="RenoLink"><a href="boost_exception_ptr_hpp.html">boost/exception_ptr.hpp</a></span>></p>
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<pre>namespace
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boost
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{
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<span class="RenoIncludeSPAN"> <span class="RenoLink"><a href="exception_ptr.html">exception_ptr</a></span> <span class="RenoLink">current_exception</span>();</span>
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}</pre>
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</div><h4>Requirements:</h4>
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<p>The <span class="RenoLink">current_exception</span> function must not be called outside of a catch block.</p>
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<p>In addition, to safely copy an exception from one thread to another, if the exception object is copied by <span class="RenoLink">current_exception</span> or <span class="RenoLink"><a href="copy_exception.html">copy_exception</a></span>, the two copies must not have shared state. Exceptions that have value-type semantics (as well as the boost::<span class="RenoLink"><a href="exception.html">exception</a></span> type itself) satisfy this requirement.</p>
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<h4>Returns:</h4>
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<div><ul><li> An <span class="RenoLink"><a href="exception_ptr.html">exception_ptr</a></span> that refers to the currently handled exception or a copy of the currently handled exception.</li>
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<li> If the function needs to allocate memory and the attempt fails, it returns an <span class="RenoLink"><a href="exception_ptr.html">exception_ptr</a></span> that refers to an instance of std::bad_alloc.</li>
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</ul></div>
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<h4>Throws:</h4>
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<p>Nothing.</p>
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<h4>Notes:</h4>
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<div><ul><li> It is unspecified whether the return values of two successive calls to <span class="RenoLink">current_exception</span> refer to the same exception object.</li>
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<li> Correct implementation of <span class="RenoLink">current_exception</span> may require compiler support (e.g. C++11 <a href="https://en.cppreference.com/w/cpp/error/current_exception">std::current_exception()</a> is used when available, as specified by Boost.Config BOOST_NO_CXX11_HDR_EXCEPTION), unless <span class="RenoLink"><a href="enable_current_exception.html">enable_current_exception</a></span> was used at the time the currently handled exception object was passed to throw. Whenever <span class="RenoLink">current_exception</span> fails to properly copy the current exception object, it returns an <span class="RenoLink"><a href="exception_ptr.html">exception_ptr</a></span> to an object of type that is as close as possible to the original exception type, using <span class="RenoLink"><a href="unknown_exception.html">unknown_exception</a></span> as a final fallback. All such types derive from boost::<span class="RenoLink"><a href="exception.html">exception</a></span>, and:<div><ul><li> if the original exception object derives from boost::<span class="RenoLink"><a href="exception.html">exception</a></span>, then the boost::<span class="RenoLink"><a href="exception.html">exception</a></span> sub-object of the object referred to by the returned <span class="RenoLink"><a href="exception_ptr.html">exception_ptr</a></span> is initialized by the boost::<span class="RenoLink"><a href="exception.html">exception</a></span> copy constructor;</li>
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<li> if available, the exception contains the std::type_info of the original exception object, accessible through <span class="RenoLink"><a href="get_error_info.html">get_error_info</a></span><<span class="RenoLink"><a href="original_exception_type.html">original_exception_type</a></span>>.</li>
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</ul></div>
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</li>
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</div><div class="RenoAutoDIV"><div class="RenoHR"><hr/></div>
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See also: <span class="RenoPageList"><a href="boost-exception.html">Boost Exception</a> | <a href="boost_exception_ptr_hpp.html">boost/exception_ptr.hpp</a> | <a href="copy_exception.html">copy_exception</a> | <a href="enable_current_exception.html">enable_current_exception</a> | <a href="frequently_asked_questions.html">Frequently Asked Questions</a> | <a href="original_exception_type.html">original_exception_type</a> | <a href="unknown_exception.html">unknown_exception</a></span>
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<!-- Copyright (c) 2006-2009 Emil Dotchevski and Reverge Studios, Inc. -->
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<small>Copyright (c) 2006-2009 by Emil Dotchevski and Reverge Studios, Inc.<br/>
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Distributed under the <a href="http://www.boost.org/LICENSE_1_0.txt">Boost Software License, Version 1.0</a>.</small>
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