155 lines
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155 lines
8.6 KiB
HTML
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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<title>Vector Accessing from C (Guile Reference Manual)</title>
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<div class="subsubsection-level-extent" id="Vector-Accessing-from-C">
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Next: <a href="Uniform-Numeric-Vectors.html" accesskey="n" rel="next">Uniform Numeric Vectors</a>, Previous: <a href="Vector-Accessors.html" accesskey="p" rel="prev">Accessing and Modifying Vector Contents</a>, Up: <a href="Vectors.html" accesskey="u" rel="up">Vectors</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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<h4 class="subsubsection" id="Vector-Accessing-from-C-1"><span>6.6.10.4 Vector Accessing from C<a class="copiable-link" href="#Vector-Accessing-from-C-1"> ¶</a></span></h4>
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<p>A vector can be read and modified from C with the functions
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<a class="ref" href="Vector-Accessors.html#x_002dscm_005fc_005fvector_005fref"><code class="code">scm_c_vector_ref</code></a> and
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<a class="ref" href="Vector-Accessors.html#x_002dscm_005fc_005fvector_005fset_005fx"><code class="code">scm_c_vector_set_x</code></a>. In addition to
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these functions, there are two other ways to access vectors from C that
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might be more efficient in certain situations: you can use the unsafe
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<em class="emph">vector macros</em>; or you can use the general framework for accessing
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all kinds of arrays (see <a class="pxref" href="Accessing-Arrays-from-C.html">Accessing Arrays from C</a>), which is more
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verbose, but can deal efficiently with all kinds of vectors (and
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arrays). For arrays of rank 1 whose backing store is a vector, you can
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use the <code class="code">scm_vector_elements</code> and
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<code class="code">scm_vector_writable_elements</code> functions as shortcuts.
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</p>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-SCM_005fSIMPLE_005fVECTOR_005fLENGTH"><span class="category-def">C Macro: </span><span><code class="def-type">size_t</code> <strong class="def-name">SCM_SIMPLE_VECTOR_LENGTH</strong> <code class="def-code-arguments">(SCM vec)</code><a class="copiable-link" href="#index-SCM_005fSIMPLE_005fVECTOR_005fLENGTH"> ¶</a></span></dt>
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<dd><p>Evaluates to the length of the vector <var class="var">vec</var>. No type
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checking is done.
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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_005fSIMPLE_005fVECTOR_005fREF"><span class="category-def">C Macro: </span><span><code class="def-type">SCM</code> <strong class="def-name">SCM_SIMPLE_VECTOR_REF</strong> <code class="def-code-arguments">(SCM vec, size_t idx)</code><a class="copiable-link" href="#index-SCM_005fSIMPLE_005fVECTOR_005fREF"> ¶</a></span></dt>
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<dd><p>Evaluates to the element at position <var class="var">idx</var> in the vector <var class="var">vec</var>.
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No type or range checking is done.
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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_005fSIMPLE_005fVECTOR_005fSET"><span class="category-def">C Macro: </span><span><code class="def-type">void</code> <strong class="def-name">SCM_SIMPLE_VECTOR_SET</strong> <code class="def-code-arguments">(SCM vec, size_t idx, SCM val)</code><a class="copiable-link" href="#index-SCM_005fSIMPLE_005fVECTOR_005fSET"> ¶</a></span></dt>
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<dd><p>Sets the element at position <var class="var">idx</var> in the vector <var class="var">vec</var> to
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<var class="var">val</var>. No type or range checking is done.
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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_005fvector_005felements"><span class="category-def">C Function: </span><span><code class="def-type">const SCM *</code> <strong class="def-name">scm_vector_elements</strong> <code class="def-code-arguments">(SCM array, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)</code><a class="copiable-link" href="#index-scm_005fvector_005felements"> ¶</a></span></dt>
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<dd><p>Acquire a <a class="ref" href="Accessing-Arrays-from-C.html">handle</a> for <var class="var">array</var> and
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return a read-only pointer to its elements. <var class="var">array</var> must be either
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a vector, or an array of rank 1 whose backing store is a vector;
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otherwise an error is signaled. The handle must eventually be released
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with <a class="ref" href="Accessing-Arrays-from-C.html#x_002dscm_005farray_005fhandle_005frelease"><code class="code">scm_array_handle_release</code></a>.
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</p>
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<p>The variables pointed to by <var class="var">lenp</var> and <var class="var">incp</var> are filled with
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the number of elements of the array and the increment (number of
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elements) between successive elements, respectively. Successive
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elements of <var class="var">array</var> need not be contiguous in their underlying
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“root vector” returned here; hence the increment is not necessarily
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equal to 1 and may well be negative too (see <a class="pxref" href="Shared-Arrays.html">Shared Arrays</a>).
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</p>
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<p>The following example shows the typical way to use this function. It
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creates a list of all elements of <var class="var">array</var> (in reverse order).
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</p>
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<div class="example">
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<pre class="example-preformatted">scm_t_array_handle handle;
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size_t i, len;
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ssize_t inc;
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const SCM *elt;
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SCM list;
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elt = scm_vector_elements (array, &handle, &len, &inc);
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list = SCM_EOL;
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for (i = 0; i < len; i++, elt += inc)
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list = scm_cons (*elt, list);
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scm_array_handle_release (&handle);
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</pre></div>
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</dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005fvector_005fwritable_005felements"><span class="category-def">C Function: </span><span><code class="def-type">SCM *</code> <strong class="def-name">scm_vector_writable_elements</strong> <code class="def-code-arguments">(SCM array, scm_t_array_handle *handle, size_t *lenp, ssize_t *incp)</code><a class="copiable-link" href="#index-scm_005fvector_005fwritable_005felements"> ¶</a></span></dt>
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<dd><p>Like <code class="code">scm_vector_elements</code> but the pointer can be used to modify
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the array.
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</p>
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<p>The following example shows the typical way to use this function. It
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fills an array with <code class="code">#t</code>.
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</p>
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<div class="example">
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<pre class="example-preformatted">scm_t_array_handle handle;
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size_t i, len;
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ssize_t inc;
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SCM *elt;
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elt = scm_vector_writable_elements (array, &handle, &len, &inc);
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for (i = 0; i < len; i++, elt += inc)
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*elt = SCM_BOOL_T;
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scm_array_handle_release (&handle);
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</pre></div>
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</dd></dl>
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</div>
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<hr>
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<p>
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Next: <a href="Uniform-Numeric-Vectors.html">Uniform Numeric Vectors</a>, Previous: <a href="Vector-Accessors.html">Accessing and Modifying Vector Contents</a>, Up: <a href="Vectors.html">Vectors</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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