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    <title>__constant</title>
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        <a xmlns="http://www.w3.org/1999/xhtml" id="__constant"></a>
        <h1>__constant</h1>
        <p>
            Address Space Qualifier.
        </p>
      </div>
      <div class="refsect2">
        <a id="synopsis"></a>
        <h3>
        </h3>
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__constant
constant
                        </td>
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      </div>
      <div class="refsect1">
        <a id="description"></a>
        <h2>Description</h2>
        <p>
OpenCL implements the following disjoint address spaces: <a class="citerefentry" href="global.html"><span class="citerefentry"><span class="refentrytitle">__global</span></span></a>, <a class="citerefentry" href="local.html"><span class="citerefentry"><span class="refentrytitle">__local</span></span></a>, <code class="function">__constant</code> and <a class="citerefentry" href="private.html"><span class="citerefentry"><span class="refentrytitle">__private</span></span></a>.
        </p>
        <p>
        </p>
        <p>
The address space qualifier may be used in variable declarations to specify the region of memory that is used to allocate the object. The C syntax for type qualifiers is extended in OpenCL to include an address space name as a valid type qualifier. If the type of an object is qualified by an address space name, the object is allocated in the specified address name; otherwise, the object is allocated in the generic address space.
        </p>
        <p>
The address space names without the __ prefix i.e. <code class="function">global</code>, <code class="function">local</code>, <code class="function">constant</code> and <code class="function">private</code> may be substituted for the corresponding address space names with the __ prefix.
        </p>
        <p>
The generic address space name for arguments to a function in a program, or local variables of a function is  <code class="function">__private</code>. All arguments to a <code class="function">__kernel</code> function shall be in the <code class="function">__private</code> address space.
        </p>
        <p>
<a class="citerefentry" href="functionQualifiers.html"><span class="citerefentry"><span class="refentrytitle">__kernel</span></span></a> function arguments declared to be a pointer of a type can point to one of the following address spaces only: <code class="function">__global</code>, <code class="function">__local</code> or <code class="function">__constant</code>. A pointer to address space A can only be assigned to a pointer to the same address space A. Casting a pointer to address space A to a pointer to address space B is illegal.
        </p>
        <p>
The <code class="function">__kernel</code> function arguments declared to be of type <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image2d_t</span></span></a></span> or <span class="type"><a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">image3d_t</span></span></a></span>
always point to the <code class="function">__global</code> address space. All program scope variables must be declared in the <code class="function">__constant</code> address space.
        </p>
        <p>
The <code class="function">__constant</code> or <code class="function">constant</code>
address space name is used to describe variables allocated in
global memory and which are accessed inside a kernel(s) as read-only variables. These read-
only variables can be accessed by all (global) work-items of the kernel during its execution. This
qualifier can be used with arguments to functions
(including <code class="function">__kernel</code> functions) that are
declared as pointers, or with local variables inside a function declared as pointers, or with global
variables. Global variables declared in the program source
with the <code class="function">__constant</code> qualifier are
required to be initialized.
        </p>
        <p>
Writes to variables declared with the <code class="function">__constant</code> address space qualifier in the OpenCL program source should be a compile-time error.
        </p>
      </div>
      <div class="refsect2">
        <a id="example1"></a>
        <h3>
            Example
        </h3>
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// declares a pointer p in the __private address space that
// points to an int object in address space __global
__global int *p;

// declares an array of 4 floats in the __private address space.
float x[4];
                        </td>
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      <div class="refsect1">
        <a id="specification"></a>
        <h2>Specification</h2>
        <p>
            <img src="pdficon_small1.gif" />
                                                 
            <a href="http://www.khronos.org/registry/cl/specs/opencl-1.0.pdf#page=150" target="OpenCL Spec">OpenCL Specification</a>
        </p>
      </div>
      <div class="refsect1">
        <a id="seealso"></a>
        <h2>Also see</h2>
        <p>
            <a class="citerefentry" href="global.html"><span class="citerefentry"><span class="refentrytitle">__global</span></span></a>, 
            <a class="citerefentry" href="local.html"><span class="citerefentry"><span class="refentrytitle">__local</span></span></a>, 
            <a class="citerefentry" href="private.html"><span class="citerefentry"><span class="refentrytitle">__private</span></span></a>
        </p>
      </div>
      <div xmlns="" class="refsect3" lang="en" xml:lang="en"><a xmlns="http://www.w3.org/1999/xhtml" id="Copyright"></a><h4 xmlns="http://www.w3.org/1999/xhtml"></h4><img xmlns="http://www.w3.org/1999/xhtml" src="KhronosLogo.jpg" /><p xmlns="http://www.w3.org/1999/xhtml"></p>Copyright © 2007-2009 The Khronos Group Inc. 
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and/or associated documentation files (the
"Materials"), to deal in the Materials without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Materials, and to
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