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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_924</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_923.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_924</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_925.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 924</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">This is the second time we've seen the unusual notationthe constructor initializerinserted between the formal parameter list and the body of a constructor. The first time was when we implemented the parameterized </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">ExtTime</font><font face="Times New Roman, Times, Serif" size="3"> class constructor (Figure 16-6). There, we used the constructor initializer to pass some of the incoming parameters to the base class constructor. Here, we use a constructor initializer to pass some of the parameters to a member object's (</font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">timeStamp's</font><font face="Times New Roman, Times, Serif" size="3">) constructor. Whether you are using inheritance or composition, the purpose of a constructor initializer is the same: to pass parameters to another constructor. The only difference is the following: With inheritance, you specify the name of the <i>base class</i> prior to the actual parameter list:</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">ExtTime::ExtTime(聽/*聽in聽*/聽int聽聽聽聽聽聽initHrs,<br />聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽/*聽in聽*/聽int聽聽聽聽聽聽initMins,<br />聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽/*聽in聽*/聽int聽聽聽聽聽聽initSecs,<br />聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽/*聽in聽*/聽ZoneType聽initZone聽)<br /><br />聽聽聽聽:聽Time(initHrs,聽initMins,聽initSecs)</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">With composition, you specify the name of the <i>member object</i> prior to the actual parameter list:</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">TimeCard::TimeCard(聽/*聽in聽*/聽long聽idNum,<br />聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽/*聽in聽*/聽int聽initHrs,<br />聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽/*聽in聽*/聽int聽initMins,<br />聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽/*聽in聽*/聽int聽initSecs聽)<br /><br />聽聽聽聽:聽timeStamp(initHrs,聽initMins,聽initSecs)</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">Furthermore, if a class has several members that are objects of classes with parameterized constructors, you form a list of constructor initializers separated by commas:</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">SomeClass::聽SomeClass聽(聽聽)<br /><br />聽聽聽聽:聽memberObject1(param1,聽param2),聽memberObject2(param3)</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">Having discussed both inheritance and composition, we can give a complete description of the order in which constructors are executed:</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"><img src="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" border="0" width="29" height="1" alt="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" /></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>Given a class X, if X is a derived class, its base class constructor is executed first. Next, constructors for member objects (if any) are executed. Finally, the body of X's constructor is executed.</i></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_923.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_924</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_925.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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