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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_783</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_782.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_783</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_784.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 783</font></td></tr></table><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td rowspan="5"><img src="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" border="0" width="96" height="1" alt="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" /></td> <td colspan="3" height="12"></td> <td rowspan="5"><img src="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" border="0" width="96" height="1" alt="3e26ecb1b6ac508ae10a0e39d2fb98b2.gif" /></td></tr><tr><td colspan="3" height="2"><table cellpadding="0" cellspacing="0" border="0"><tr><td></td></tr></table></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2">Hierarchical Records Records in which at least one of the components is itself a record.</font></td><td></td></tr><tr><td colspan="3" height="2"><table cellpadding="0" cellspacing="0" border="0"><tr><td></td></tr></table></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">Let's look at an example where a hierarchical structure is appropriate. A small machine shop keeps information about each of its machines. There is descriptive information, such as the identification number, a description of the machine, the purchase date, and the cost. Statistical information is also kept, such as the number of down days, the failure rate, and the date of last service. What is a reasonable way of representing all this information? First, let's look at a flat (nonhierarchical) record structure that holds this information.</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">typedef聽char聽String50[51];<br /><br />struct聽MachineRec<br />{<br />聽聽聽聽int聽聽聽聽聽聽idNumber;<br />聽聽聽聽String50聽description;<br />聽聽聽聽float聽聽聽聽failRate;<br />聽聽聽聽int聽聽聽聽聽聽lastServicedMonth;聽聽//聽Assume聽1..12<br />聽聽聽聽int聽聽聽聽聽聽lastServicedDay;聽聽聽聽//聽Assume聽1..31<br />聽聽聽聽int聽聽聽聽聽聽lastServicedYear;聽聽聽//聽Assume聽1900..2050<br />聽聽聽聽int聽聽聽聽聽聽downDays;<br />聽聽聽聽int聽聽聽聽聽聽purchaseDateMonth;聽聽//聽Assume聽1..12<br />聽聽聽聽int聽聽聽聽聽聽purchaseDateDay;聽聽聽聽//聽Assume聽1..31<br />聽聽聽聽int聽聽聽聽聽聽purchaseDateYear;聽聽聽//聽Assume聽1900..2050<br />聽聽聽聽float聽聽聽聽cost;<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">Type </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">MachineRec</font><font face="Times New Roman, Times, Serif" size="3"> has 11 members. There is so much detailed information here that it is difficult to quickly get a feeling for what the record represents. Let's see if we can reorganize it into a hierarchical structure that makes more sense. We can divide the information into two groups: information that changes and information that does not. There are also two dates to be kept: date of purchase and date of last service. These observations suggest use of a record describing a date, a record describing the statistical data, and an overall record containing the other two as components. The following type declaration reflects this structure.</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">const聽int聽NUM_MACHINES聽=聽25;<br /><br />typedef聽char聽String50[51];<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_782.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_783</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_784.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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