Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
Opaque pointer
open-in-new
<p>In <a href="/facts/Computer_programming/QmSsFnu0">computer programming</a>, an opaque pointer is a special case of an <a href="/facts/Opaque_data_type/yMAgh1Kj">opaque data type</a>, a <a href="/facts/Data_type/fcx5hgVL">data type</a> declared to be a <a href="/facts/Pointer_(computer_science)/fPoNzy9b">pointer</a> to a <a href="/facts/Record_(computer_science)/1fvSgenB">record</a> or <a href="/facts/Data_structure/yNsNvL1I">data structure</a> of some unspecified type. </p><p>Opaque pointers are present in several <a href="/facts/Programming_language/cWTYbgWa">programming languages</a> including <a href="/facts/Ada_(programming_language)/Y2yHel4l">Ada</a>, <a href="/facts/C_(programming_language)/Ky2No763">C</a>, <a href="/facts/C%252B%252B/Et0F2qn9">C++</a>, <a href="/facts/D_(programming_language)/4qIzRjkF">D</a> and <a href="/facts/Modula-2/DFyUTdAq">Modula-2</a>. </p><p>If the language is <a href="/facts/Strong_typing/WYexudnr">strongly typed</a>, <a href="/facts/Computer_program/e38jH9N9">programs</a> and <a href="/facts/Subroutine/9vFJrg0A">procedures</a> that have no other information about an opaque pointer type <i>T</i> can still declare <a href="/facts/Variable_(programming)/VoCKtwml">variables</a>, <a href="/facts/Array_data_structure/BKGvF8AM">arrays</a>, and record fields of type <i>T</i>, assign values of that type, and compare those values for equality. However, they will not be able to <a href="/facts/Reference_(computer_science)/1vm2Bph1">de-reference</a> such a pointer, and can only change the object's content by calling some procedure that has the missing information. </p><p>Opaque pointers are a way to hide the <a href="/facts/Implementation_(computing)/IH1KXgP3">implementation</a> details of an <a href="/facts/Interface_(computer_science)/zdfp8unT">interface</a> from ordinary clients, so that the <a href="/facts/Implementation_(computing)/IH1KXgP3">implementation</a> may be changed without the need to recompile the <a href="/facts/Module_(programming)/sNoqKvRD">modules</a> using it. This benefits the programmer as well since a simple interface can be created, and most details can be hidden in another file. This is important for providing <a href="/facts/Binary_code_compatibility/7lkFAUfv">binary code compatibility</a> through different versions of a <a href="/facts/Shared_library/xRzL3P7q">shared library</a>, for example. </p><p>This technique is described in <i><a href="/facts/Design_Patterns/sYDxSGc9">Design Patterns</a></i> as the <a href="/facts/Bridge_pattern/AEekA3Tv">Bridge pattern</a>. It is sometimes referred to as "<a href="/facts/Handle_(computing)/gKL1X2sX">handle</a> classes", the "Pimpl idiom" (for "pointer to implementation idiom"), "Compiler firewall idiom", "d-pointer" or "Cheshire Cat", especially among the C++ community. </p>