key_aspects_of_c++.htm

acis说明文档

<p>Example. Overloaded Operators
</p><p>ACIS makes use of the fact that C++ is a strongly typed to enforce rules of combination  SPAvector instance.
</p>
<pre class="source-cpp">C++ Example <span class="kw5">SPAposition</span> p1 <span class="br0">&#40;</span><span class="nu0">3</span>, <span class="nu0">4</span>, <span class="nu0">5</span><span class="br0">&#41;</span>; <span class="kw5">SPAposition</span> p2 <span class="br0">&#40;</span><span class="nu0">6</span>, <span class="nu0">7</span>, <span class="nu0">8</span><span class="br0">&#41;</span>; <span class="kw5">SPAposition</span> p3 = p1 + p2; <span class="co1">// Error: this does not compile SPAvector v1 (10, 20 , 30); SPAposition p4 = p1 + v1; // creates a new position offset from                            // position p1 by vector v1.</span></pre>
<p>Example. Using C++ Strong Types
</p>
<a name="Overloading_Class_new_and_delete"></a><h2> <span class="mw-headline"> Overloading Class new and delete </span></h2>
<p>ACIS overloads the C++ new operator to allocate space on the portion of the heap controlled by ACIS  ENTITY defines its own new and delete operators that the ACIS free list manager. (These operators are supplied by the ENTITY_FUNCTIONS and UTILITY_DEF macros.)
</p><p>When working with Microsoft Developer Studio and/or MFC, the beginning of the file may have been enhanced by Microsoft during a _DEBUG compile. Sometimes you will see:
</p>
<pre class="source-cpp">_DEBUG  <span class="kw3">new</span> <span class="kw7">DEBUG_NEW</span> <span class="co1">// ... other code...</span></pre>
<p>This interferes with the ACIS overloading of new for the entities  ENTITY objects to another file.
</p><p>In fact it is an issue when trying to instantiate any object derived from an ACIS entity in MFC API_END around the ENTITY creation code, so it is best to do the allocation in an API function.
</p>
<pre class="source-cpp"><span class="kw5">outcome</span> api_make_attrib<span class="br0">&#40;</span><span class="kw7">ENTITY</span>*&amp; ent, 
                        <span class="kw7">ATTRIB_GEN_INTEGER</span>*&amp; attrib, 
                        <span class="kw4">char</span>*&amp; name, int&amp; value<span class="br0">&#41;</span> 
<span class="br0">&#123;</span>
     <span class="kw6">API_BEGIN</span>
         <span class="kw3">new</span> attrib = <span class="kw3">new</span> <span class="kw7">ATTRIB_GEN_INTEGER</span><span class="br0">&#40;</span>ent, name, value<span class="br0">&#41;</span>;
         <span class="kw3">new</span> <span class="kw7">DEBUG_NEW</span>     
     <span class="kw6">API_END</span> 
<span class="br0">&#125;</span></pre>
<a name="Overloading_API_Functions"></a><h2> <span class="mw-headline"> Overloading API Functions </span></h2>
<p>Although the discussion so far in this section has been about C++ classes and their associated data elements and methods, much of this holds true for the API function interface.
</p><p>The API functions form the primary interface to ACIS and add an additional level of interface stability. Class methods may change from release to release. However, the API interface remain consistent from release to release. The API functions are often wrappers for C++ class methods or groupings of methods.
</p><p>Like C++ class methods, API functions can be overloaded. This means that a single name can refer to multiple forms of an API function, with the differences being in the number of arguments and/or in the argument types. The distinction between the overloaded forms of API functions happens at compile time.
</p>
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