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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><link rel="STYLESHEET" type="text/css" href="wrs.css"><title> C++ Development </title></head><body bgcolor="FFFFFF"><p class="navbar" align="right"><a href="index.html"><img border="0" alt="[Contents]" src="icons/contents.gif"></a><a href="GuideIX.html"><img border="0" alt="[Index]" src="icons/index.gif"></a><a href="c-wfc.html"><img border="0" alt="[Top]" src="icons/top.gif"></a><a href="c-wfc3.html"><img border="0" alt="[Prev]" src="icons/prev.gif"></a><a href="c-wfc5.html"><img border="0" alt="[Next]" src="icons/next.gif"></a></p><font face="Helvetica, sans-serif" class="sans"><h3 class="H2"><i><a name="84638">5.4 Example</a></i></h3></font><dl class="margin"><dl class="margin"><dd><p class="Body"><a name="84642"> </a><a href="c-wfc4.html#84646">Example 5-2</a> exercises various C++ features including the Standard Template Library, user defined templates, Run-Time Type Identification, and exception handling. To try it out, create a project containing <b class="file">factory.cpp</b> and <b class="file">factory.h</b> and build and download <b class="file">linkedObjs.o</b>. At the shell type:</p><dl class="margin"><dd><pre class="Code2"><b><a name="84643"></b><tt class="output">-></tt><b> testFactory</a></b></pre></dl><dd><p class="Body"><a name="84644"> </a>Full documentation on what you should except to see is given in the source code.</p></dl></dl><h4 class="EntityTitle"><a name="84646"><font face="Helvetica, sans-serif" size="-1" class="sans">Example 5-2: Code Factory Example</font></a></h4><dl class="margin"><dl class="margin"><dd><pre class="Code"><b><a name="84647">/* factory.cpp - implements an object factory */ /* Copyright 1993-1998 Wind River Systems, Inc. */ /* modification history -------------------- 01a,05oct98,sn wrote */ /* DESCRIPTION We implement an "object factory". The first step is to give classes human-readable names by registering them with a "global class registry". Then objects of a named type may be created and registered with an "object registry". </a></b><dd> <b><a name="84648">This gives us an opportunity to exercise various C++ features: * Standard Template Library A "map" is used as the basis for the various registries. * User defined templates The class registry and object registry are both based on a generic registry type. * Run Time Type Checking We provide a function to determine the type of a registered object using "dynamic_cast". * Exception Handling If we attempt to cast to the "wrong" type we have to handle a C++ exception. We provide a C interface to facilitate easy testing from the Wind Shell. Here is an example test run (you can run this whole test through the function testFactory()): -> classRegistryShow Showing Class Registry ... Name Address ========================================================= blue_t 0x6b1c7a0 green_t 0x6b1c790 red_t 0x6b1c7b0 -> objectRegistryShow Showing Object Registry ... Name Address ========================================================= -> objectCreate "green_t", "bob" Creating an object called 'bob' of type 'green_t' -> objectCreate "red_t", "bill" Creating an object called 'bill' of type 'red_t' -> objectRegistryShow Showing Object Registry ... Name Address ========================================================= bill 0x6b1abf8 bob 0x6b1ac18 -> objectTypeShowByName "bob" Looking up object 'bob' Attempting to ascertain type of object at 0x6b1ac18 Attempting a dynamic_cast to red_t ... dynamic_cast threw an exception ... caught here! Attempting a dynamic_cast to blue_t ... dynamic_cast threw an exception ... caught here! Attempting a dynamic_cast to green_t ... Cast to green_t succeeded! green. */ /* includes */ #include "factory.h" /* locals */ /* pointer to the global class registry */ LOCAL class_registry_t* pClassRegistry; /* pointer to the global object registry */ LOCAL object_registry_t* pObjectRegistry; /************************************************************************* * * testFactory - an example test run * */ void testFactory () { cout << "classRegistryShow ()" << endl; classRegistryShow (); cout << "objectRegistryShow ()" << endl; objectRegistryShow (); cout << "objectCreate (\"green_t\", \"bob\")" << endl; objectCreate ("green_t", "bob"); cout << "objectCreate (\"red_t\", \"bill\")" << endl; objectCreate ("red_t", "bill"); cout << "objectRegistryShow ()" << endl; objectRegistryShow (); cout << "objectTypeShowByName (\"bob\")" << endl; objectTypeShowByName ("bob"); } /************************************************************************* * * class_registry_t::create - create an object of type className * * Look up 'className' in this registry. If it exists then * create an object of this type by using the registered class factory; * otherwise return NULL. * * RETURNS : pointer to new object of type className or NULL. */ object_t* class_registry_t::create ( string className ) { object_factory_t* pFactory = lookup (className); if (pFactory != NULL) { return lookup (className)-> create (); } else { cout << "No such class in Class Registry. " << endl; return NULL; } } /************************************************************************* * * classRegistryGet - get a reference to the global class registry * * Create and populate a new class registry if necessary. * * RETURNS : a reference to the global class registry */ LOCAL class_registry_t& classRegistryGet () { if (pClassRegistry == NULL) { pClassRegistry = new class_registry_t; pClassRegistry -> insert ("red_t", new red_factory_t); pClassRegistry -> insert ("blue_t", new blue_factory_t); pClassRegistry -> insert ("green_t", new green_factory_t); } return *pClassRegistry; } /************************************************************************* * * objectRegistryGet - get a reference to the global object registry * * Create a new object registry if necessary. * * RETURNS : a reference to the global object registry */ LOCAL object_registry_t& objectRegistryGet () { if (pObjectRegistry == NULL) { pObjectRegistry = new object_registry_t; } return *pObjectRegistry; } /************************************************************************* * * objectCreate - create an object of a given type * * Use the class factory registered in the global class registry * under 'className' to create a new object. Register this object * in the global object registry under 'object name'. * * RETURNS : object of type className */ object_t* objectCreate ( char* className, char* objectName ) { cout << "Creating an object called '" << objectName << "'" << " of type '" << className << "'" << endl; object_t* pObject = classRegistryGet().create (className); if (pObject != NULL) { objectRegistryGet().insert(objectName, pObject); } else { cout << "Could not create object. Sorry. " << endl; } return pObject; } /************************************************************************* * * isRed * isBlue - is anObject a reference to an object of the specified type? * isGreen * * Try a dynamic_cast. If this succeeds then return TRUE. If it fails * then catch the resulting exception and return FALSE. * * RETURNS : TRUE or FALSE */ /* isRed */ LOCAL BOOL isRed (object_t& anObject) { try { cout << "Attempting a dynamic_cast to red_t ..." << endl; dynamic_cast<red_t&> (anObject); cout << "Cast to red_t succeeded!" << endl; return TRUE; } catch (exception) { cout << "dynamic_cast threw an exception ... caught here!" << endl; return FALSE; } } /* isBlue */</a></b><dd> <b><a name="84649">LOCAL BOOL isBlue (object_t& anObject) { try { cout << "Attempting a dynamic_cast to blue_t ..." << endl; dynamic_cast<blue_t&> (anObject); cout << "Cast to blue_t succeeded!" << endl; return TRUE; } catch (exception) { cout << "dynamic_cast threw an exception ... caught here!" << endl; return FALSE; } } /* isGreen */ LOCAL BOOL isGreen (object_t& anObject) { try { cout << "Attempting a dynamic_cast to green_t ..." << endl; dynamic_cast<green_t&> (anObject); cout << "Cast to green_t succeeded!" << endl; return TRUE; } catch (exception) { ⌨️ 快捷键说明
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