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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_990</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_989.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_990</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_991.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 990</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">erence is the one that we have been using all along and continue to use throughout the book.</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">By now, you have probably noticed that the ampersand (</font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">&</font><font face="Times New Roman, Times, Serif" size="3">) has several meanings in the C++ language. To avoid errors, it pays to keep these meanings distinct from each other. Below is a table that summarizes the different uses of the ampersand. Note that a <i>prefix</i> operator is one that precedes its operand(s), an <i>infix</i> operator lies between its operands, and a <i>postfix</i> operator comes after its operand(s).</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" width="528" cellpadding="7"><tr><td valign="middle"><font face="Times New Roman, Times, Serif" size="2"><i>Position</i></font></td><td valign="middle"><font face="Times New Roman, Times, Serif" size="2"><i>Usage</i></font></td><td valign="middle"><font face="Times New Roman, Times, Serif" size="2"><i>Meaning</i></font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Prefix</font></td><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">&</font><font face="Times New Roman, Times, Serif" size="2"> Variables</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Address-of operation</font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Infix</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Expression </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">&</font><font face="Times New Roman, Times, Serif" size="2"> Expression</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Bitwise AND operation (mentioned, but not explored, in Chapter 10)</font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Infix</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Expression </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">&&</font><font face="Times New Roman, Times, Serif" size="2"> Expression</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Logical AND operation</font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Postfix</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">DataType&</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Data type (specifically, a reference type)<br /><i>Exception:</i> To declare two variables of reference type, the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">&</font><font face="Times New Roman, Times, Serif" size="2"> is attached to the variable name: </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">int聽&var1</font><font face="Times New Roman, Times, Serif" size="2">, </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">&var2</font><font face="Times New Roman, Times, Serif" size="2">;</font></td></tr></table></td></tr></table><br /><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="17"></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">Classes and Dynamic Data</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">When programmers use C++ classes, it is often useful for class objects to create dynamic data on the free store. Let's consider writing a variation of the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">DateType</font><font face="Times New Roman, Times, Serif" size="3"> class of Chapter 15. In addition to a month, day, and year, we want each class object to store a message string such as My birthday or Meet Al. When a client program prints a date, this message string will be printed next to the date. To keep the example simple, we'll supply only a bare minimum of public member functions. We begin with the class declaration for a </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">Date聽class</font><font face="Times New Roman, Times, Serif" size="3">, abbreviated by leaving out the function preconditions and postconditions.</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Date<br />{<br />public:<br />聽聽聽聽void聽Print()聽const;聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽//聽Output聽operation<br />聽聽聽聽Date(聽/*聽in聽*/聽int聽聽聽聽聽聽聽聽聽initMo,聽聽聽聽聽聽//聽Constructor<br />聽聽聽聽聽聽聽聽聽聽/*聽in聽*/聽int聽聽聽聽聽聽聽聽聽initDay,<br />聽聽聽聽聽聽聽聽聽聽/*聽in聽*/聽int聽聽聽聽聽聽聽聽聽initYr,<br />聽聽聽聽聽聽聽聽聽聽/*聽in聽*/聽const聽char*聽msgStr聽);<br />private:<br />聽聽聽聽聽聽聽int聽聽聽mo;<br />聽聽聽聽聽聽聽int聽聽聽day;<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_989.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_990</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_991.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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