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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_1023</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_1022.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_1023</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_1024.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 1023</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">The聽class聽constructor聽DynArray聽(In:聽arrSize)</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="470" 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">IF聽arrSize聽<<聽1<br />聽聽聽Print聽error聽message<br />聽聽聽Halt聽the聽program<br />Set聽size聽=聽arrSize<br />Set聽arr聽=聽new聽int[size]聽聽聽//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-1<br />聽聽Set聽arr[i]聽=聽0</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">The聽class聽destructor聽~DynArray聽()</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table cellpadding="0" cellspacing="0" border="0" width="100%"><tr><td height="12"></td></tr><tr><td><table cellspacing="0" border="0" width="326" 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">Deallocate聽the聽array聽pointed聽to聽by聽arr</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></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">In the constructor, we allocate an integer array of </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">arrSize</font><font face="Times New Roman, Times, Serif" size="3"> elements and store its base address into the pointer variable </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">arr</font><font face="Times New Roman, Times, Serif" size="3">. Remember that in C++ any pointer can be indexed by attaching an index expression in brackets. Therefore, the assignment statement</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="Courier New, Courier, Mono New, Courier, Mono" size="2">arr[i]聽=聽0;</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">does exactly what we want it to: it stores zero into element </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">i</font><font face="Times New Roman, Times, Serif" size="3"> of the array pointed to by </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">arr</font><font face="Times New Roman, Times, Serif" size="3">.</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">Testing: Three things should be tested in the constructor: the two If statements and the initialization loop. To test the first If statement, we should try different values of the parameter </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">arrSize</font><font face="Times New Roman, Times, Serif" size="3">: negative, zero, and positive. Negative and zero values should cause the program to halt. Testing the second If statement may or may not prove fruitful, depending on a particular compiler and machine. On some machines, passing a huge value of </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">arrSize</font><font face="Times New Roman, Times, Serif" size="3"> may cause the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">new</font><font face="Times New Roman, Times, Serif" size="3"> operator to return </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">NULL</font><font face="Times New Roman, Times, Serif" size="3"> if there is not enough room on the free store. Other machines use a concept called <i>virtual memory,</i> which lets the machine borrow space on a disk device as if the disk were memory. In this case, the size of the free store is essentially unbounded, so the If test will always succeed. To test the initialization loop, it would suf-</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_1022.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_1023</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_1024.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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