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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <title>page_1025</title> <link rel="stylesheet" href="reset.css" type="text/css" media="all"> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> </head> <body> <table summary="top nav" border="0" width="100%"> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_1024.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_1025</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_1026.html">next page ></a></td> </tr> <tr> <td align="left" colspan="3" style="background: #ffffff; padding: 20px;"> <table border="0" width="100%" cellpadding="0"><tr><td align="center"> <table border="0" cellpadding="2" cellspacing="0" width="100%"><tr><td align="left"></td> <td align="right"></td> </tr></table></td></tr><tr><td align="left"><p></p><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="right"><font face="Times New Roman, Times, Serif" size="2" color="#FF0000">Page 1025</font></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3"><i>The class copy-constructor:</i> This function is called whenever a new class object is created <i>and</i> initialized to be a copy of an existing class object. As with the basic class constructor, the function attempts to allocate a new dynamic array on the free store and must check the resulting pointer to see if the allocation succeeded.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">The聽class聽copy-constructor聽DynArray聽(In:聽array2)</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table cellspacing="0" border="0" width="442" cellpadding="4"><tr><td valign="top"><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">Set聽size聽=聽array2.size<br />Set聽arr聽=聽new聽int[size]聽聽//聽Allocate聽a聽dynamic聽array<br />IF聽arr聽is聽NULL<br />聽聽聽Print聽error聽message<br />聽聽聽Halt聽the聽program<br />FOR聽i聽going聽from聽0聽through聽size聽-聽1<br />聽聽聽Set聽arr[i]聽=聽array2.arr[i]</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td></tr></table><br /><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">Testing: A copy-constructor is implicitly invoked whenever a class object is passed by value as a parameter, is returned as a function value, or is initialized by another class object in a declaration. To test the copyconstructor, you could write a function that receives a </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">DynArray</font><font face="Times New Roman, Times, Serif" size="3"> object by value, outputs the contents (to confirm that the values of the array elements are the same as in the caller's actual parameter), and modifies some of the array elements. On return from the function, the calling code should print out the contents of the original array, which should be unchanged from the time before the function call. In other words, you want to verify that when the function modified some array elements, it was working on a <i>copy</i> of the actual parameter, not on the actual parameter itself.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3"><i>The</i> </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">CopyFrom</font><font face="Times New Roman, Times, Serif" size="3"> <i>function:</i> This function is nearly the same as the copyconstructor; it performs a deep copy of one class object to another. The important difference is that, whereas the copy-constructor creates a <i>new</i> class object to copy to, the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">CopyFrom</font><font face="Times New Roman, Times, Serif" size="3"> function is applied to an <i>existing</i> class object. The only difference in the two algorithms, then, is that </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">CopyFrom</font><font face="Times New Roman, Times, Serif" size="3"> must begin by deallocating the dynamic array that is currently pointed to.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td></tr></table><p><font size="0"></font></p>聽 </td> </tr> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_1024.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_1025</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_1026.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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