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Wrapper library

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Wrapper libraries (or library wrappers) consist of a thin layer of code (a "<a href="Shim_(computing)" title="Shim (computing)">shim</a>") which translates a <a href="Library_(computing)" title="Library (computing)">library</a>'s existing interface into a compatible interface. This is done for several reasons:

<ul><li>To refine a poorly designed or complicated interface</li>

<li>Allow code to work together which otherwise cannot (e.g. incompatible data formats)</li>

<li>Enable cross language and/or <a href="Run-time_system" class="mw-redirect" title="Run-time system">runtime</a> interoperability</li></ul>

Wrapper libraries can be implemented using the <a href="Adapter_pattern" title="Adapter pattern">adapter</a>, <a href="Facade_pattern" title="Facade pattern">façade</a>, and to a lesser extent, <a href="Proxy_pattern" title="Proxy pattern">proxy</a> <a href="Design_pattern_(computer_science)" class="mw-redirect" title="Design pattern (computer science)">design patterns</a>.

<div class="mw-heading mw-heading2"><h2 id="Structure_and_implementation">Structure and implementation</h2></div>

The specific way in which a wrapper library is implemented is highly specific to the environment it is being written in and the scenarios which it intends to address. This is especially true in the case when <a href="#Cross-language.2Fruntime_interoperability">cross-language/runtime interoperability</a> is a consideration.

<div class="mw-heading mw-heading3"><h3 id="Example">Example</h3></div>

The following provides a general illustration of a common wrapper library implementation. In this example, a <a href="C%2B%2B" title="C++">C++</a> interface acts as a "wrapper" around a <a href="C_(programming_language)" title="C (programming language)">C</a> interface.

<div class="mw-heading mw-heading4"><h4 id="C_interface">C interface</h4></div>

<div class="mw-highlight mw-highlight-lang-c mw-content-ltr" dir="ltr"><pre>int pthread_mutex_init(pthread_mutex_t * mutex , pthread_mutexattr_t * attr);

int pthread_mutex_destroy (pthread_mutex_t * mutex);

int pthread_mutex_lock (pthread_mutex_t * mutex );

int pthread_mutex_unlock (pthread_mutex_t * mutex );

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<div class="mw-heading mw-heading4"><h4 id="C++_wrapper">C++ wrapper</h4></div>

<div class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><pre>class Mutex

{

pthread_mutex_t mutex;

public:

Mutex()

{

pthread_mutex_init(&mutex, 0);

}

~Mutex()

{

pthread_mutex_destroy(&mutex);

}

private:

friend class Lock;

void lock()

{

pthread_mutex_lock(&mutex);

}

void unlock()

{

pthread_mutex_unlock(&mutex);

}

};

class Lock

{

private:

Mutex &mutex;

public:

Lock(Mutex &mutex): mutex{mutex}

{

mutex.lock();

}

~Lock()

{

mutex.unlock();

}

};

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The original C interface can be regarded as error prone, particularly in the case where users of the library forget to unlock an already locked mutex. The new interface effectively utilizes <a href="Resource_acquisition_is_initialization" title="Resource acquisition is initialization">resource acquisition is initialization</a> (RAII) in the new <style data-mw-deduplicate="TemplateStyles:r886049734">

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</style>Mutex and Lock classes to ensure Mutexs are eventually unlocked and pthread_mutex_t objects are automatically released.

The above code closely mimics the implementation of boost::scoped_lock and boost::mutex which are part of the <a rel="nofollow" class="external text" href="http://www.boost.org/doc/libs/1_38_0/doc/html/thread.html">boost::thread</a> library.

<div class="mw-heading mw-heading3"><h3 id="Driver_wrappers">Driver wrappers</h3></div>

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</style><div role="note" class="hatnote navigation-not-searchable">Further information: <a href="Driver_wrapper" title="Driver wrapper">Driver wrapper</a></div>

<div class="mw-heading mw-heading2"><h2 id="Cross-language/runtime_interoperability">Cross-language/runtime interoperability</h2></div>

Some wrapper libraries exist to act as a bridge between a client application and a library written using an incompatible technology. For instance, a <a href="Java_(programming_language)" title="Java (programming language)">Java</a> application may need to execute a <a href="System_call" title="System call">system call</a>. However system calls are typically exposed as C library functions. To resolve this issue Java implements wrapper libraries which make these system calls callable from a Java application.

In order to achieve this, languages like Java provide a mechanism called <a href="Foreign_function_interface" title="Foreign function interface">foreign function interface</a> that makes this possible. Some examples of these mechanisms include:

<ul><li><a href="Java_Native_Interface" title="Java Native Interface">Java Native Interface (JNI)</a></li>

<li><a href="Java_Native_Access" title="Java Native Access">Java Native Access (JNA)</a></li>

<li><a rel="nofollow" class="external text" href="https://docs.python.org/library/ctypes.html">A foreign function library for Python</a></li>

<li><a href="Managed_Extensions_for_C%2B%2B" title="Managed Extensions for C++">Managed Extensions</a></li>

<li><a href="SWIG" title="SWIG">SWIG (Simplified Wrapper and Interface Generator)</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="Existing_wrapper_libraries">Existing wrapper libraries</h2></div>

Some examples of existing wrapper libraries:

<ul><li><a rel="nofollow" class="external text" href="http://sourceware.org/pthreads-win32/">Pthreads for WIN32</a></li>

<li><a rel="nofollow" class="external text" href="https://pyopengl.sourceforge.net/">OpenGL Bindings for Python</a></li>

<li><a rel="nofollow" class="external text" href="http://www.tangentsoft.net/mysql++/">MySQL++</a></li>

<li><a rel="nofollow" class="external text" href="https://github.com/bytedeco/javacv/">JavaCV</a></li>

<li><a href="WineD3D" class="mw-redirect" title="WineD3D">WineD3D</a></li></ul>

<ul><li><a href="Wrapper_function" title="Wrapper function">Wrapper function</a></li>

<li><a href="Wrapper_pattern" class="mw-redirect" title="Wrapper pattern">Wrapper pattern</a></li>

This article is issued from <a class="external text" title="Last edited on 2025-04-23" href="https://en.wikipedia.org/wiki/?title=Wrapper_library&oldid=1287021467">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

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