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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_1019</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_1018.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_1019</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_1020.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 1019</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">function, to retrieve the value of an array element. We want to enhance the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">IntArray</font><font face="Times New Roman, Times, Serif" size="3"> class so that a client of the class can create an array of <i>any</i> sizea size that is not bounded by a constant </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">MAX_SIZE</font><font face="Times New Roman, Times, Serif" size="3">. Furthermore, the client should be able to specify the array size at execution time rather than at compile time.</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">In this case study, we omit the Input and Output sections because we are developing only a C++ class, not a complete program. Instead, we include two sections entitled Specification of the Class and Implementation of the Class.</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">Discussion: In Chapter 15's </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">IntArray</font><font face="Times New Roman, Times, Serif" size="3"> class, the private data include a fixed-size array of </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">MAX_SIZE</font><font face="Times New Roman, Times, Serif" size="3"> (which is 200) elements:</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">class聽IntArray<br />{<br />聽聽.<br />聽聽.<br />聽聽.<br />private:<br />聽聽聽聽int聽arr[MAX-SIZE];<br />聽聽聽聽int聽size;<br />};</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">Each class object contains an array of exactly 200 elements, whether the client needs that many or not. If the client requires fewer than 200 elements, then memory is wasted. If more than 200 elements are needed, the class cannot be used.</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 disadvantage of any built-in array, such as arr in the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">IntArray</font><font face="Times New Roman, Times, Serif" size="3"> class, is that its size must be known <i>statically</i> (at compile time). In this case study, we want to be able to specify the array size <i>dynamically</i> (at execution time). Therefore, we must design and implement a class (call it </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">DynArray</font><font face="Times New Roman, Times, Serif" size="3">) that allocates dynamic data on the free storespecifically, an integer array of any size specified by the client code. The private part of our class will no longer include an entire array; rather, it will include a pointer to a dynamically allocated array:</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">class聽DynArray<br />{<br />聽聽.<br />聽聽.<br />聽聽.<br />private:<br />聽聽聽聽int*聽arr;<br />聽聽聽聽int聽聽size;<br />};</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_1018.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_1019</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_1020.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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