120 lines
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120 lines
7 KiB
HTML
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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<title>Exceptions and C (Guile Reference Manual)</title>
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<div class="subsubsection-level-extent" id="Exceptions-and-C">
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<div class="nav-panel">
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<p>
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Previous: <a href="Throw-and-Catch.html" accesskey="p" rel="prev">Throw and Catch</a>, Up: <a href="Exceptions.html" accesskey="u" rel="up">Exceptions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<h4 class="subsubsection" id="Exceptions-and-C-1"><span>6.11.8.4 Exceptions and C<a class="copiable-link" href="#Exceptions-and-C-1"> ¶</a></span></h4>
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<p>There are some specific versions of Guile’s original <code class="code">catch</code> and
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<code class="code">with-throw-handler</code> exception-handling primitives that are still
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widely used in C code.
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</p>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005fc_005fcatch"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_c_catch</strong> <code class="def-code-arguments">(SCM tag, scm_t_catch_body body, void *body_data, scm_t_catch_handler handler, void *handler_data, scm_t_catch_handler pre_unwind_handler, void *pre_unwind_handler_data)</code><a class="copiable-link" href="#index-scm_005fc_005fcatch"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-scm_005finternal_005fcatch"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_internal_catch</strong> <code class="def-code-arguments">(SCM tag, scm_t_catch_body body, void *body_data, scm_t_catch_handler handler, void *handler_data)</code><a class="copiable-link" href="#index-scm_005finternal_005fcatch"> ¶</a></span></dt>
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<dd><p>The above <code class="code">scm_catch_with_pre_unwind_handler</code> and <code class="code">scm_catch</code>
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take Scheme procedures as body and handler arguments.
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<code class="code">scm_c_catch</code> and <code class="code">scm_internal_catch</code> are equivalents taking
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C functions.
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</p>
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<p><var class="var">body</var> is called as <code class="code"><var class="var">body</var> (<var class="var">body_data</var>)</code> with a catch
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on exceptions of the given <var class="var">tag</var> type. If an exception is caught,
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<var class="var">pre_unwind_handler</var> and <var class="var">handler</var> are called as
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<code class="code"><var class="var">handler</var> (<var class="var">handler_data</var>, <var class="var">key</var>, <var class="var">args</var>)</code>.
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<var class="var">key</var> and <var class="var">args</var> are the <code class="code">SCM</code> key and argument list from
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the <code class="code">throw</code>.
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</p>
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<a class="index-entry-id" id="index-scm_005ft_005fcatch_005fbody"></a>
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<a class="index-entry-id" id="index-scm_005ft_005fcatch_005fhandler"></a>
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<p><var class="var">body</var> and <var class="var">handler</var> should have the following prototypes.
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<code class="code">scm_t_catch_body</code> and <code class="code">scm_t_catch_handler</code> are pointer
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typedefs for these.
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</p>
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<div class="example">
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<pre class="example-preformatted">SCM body (void *data);
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SCM handler (void *data, SCM key, SCM args);
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</pre></div>
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<p>The <var class="var">body_data</var> and <var class="var">handler_data</var> parameters are passed to
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the respective calls so an application can communicate extra
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information to those functions.
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</p>
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<p>If the data consists of an <code class="code">SCM</code> object, care should be taken that
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it isn’t garbage collected while still required. If the <code class="code">SCM</code> is a
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local C variable, one way to protect it is to pass a pointer to that
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variable as the data parameter, since the C compiler will then know the
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value must be held on the stack. Another way is to use
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<code class="code">scm_remember_upto_here_1</code> (see <a class="pxref" href="Foreign-Object-Memory-Management.html">Foreign Object Memory Management</a>).
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005fc_005fwith_005fthrow_005fhandler"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_c_with_throw_handler</strong> <code class="def-code-arguments">(SCM tag, scm_t_catch_body body, void *body_data, scm_t_catch_handler handler, void *handler_data, int lazy_catch_p)</code><a class="copiable-link" href="#index-scm_005fc_005fwith_005fthrow_005fhandler"> ¶</a></span></dt>
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<dd><p>The above <code class="code">scm_with_throw_handler</code> takes Scheme procedures as body
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(thunk) and handler arguments. <code class="code">scm_c_with_throw_handler</code> is an
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equivalent taking C functions. See <code class="code">scm_c_catch</code>
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(see <a class="pxref" href="#Exceptions-and-C">Exceptions and C</a>) for a description of the parameters, the
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behavior however of course follows <code class="code">with-throw-handler</code>.
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</p></dd></dl>
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</div>
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<hr>
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<div class="nav-panel">
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<p>
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Previous: <a href="Throw-and-Catch.html">Throw and Catch</a>, Up: <a href="Exceptions.html">Exceptions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</body>
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