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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_372</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_371.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_372</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_373.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 372</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 message is potentially confusing. It doesn't mean that </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">studentCount</font><font face="Times New Roman, Times, Serif" size="3"> <i>is</i> greater than zero. In fact, it's just the opposite. The message tells you that the assertion </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">studentCount聽>聽0</font><font face="Times New Roman, Times, Serif" size="3"> is FALSE.)</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">Executable assertions have a profound advantage over assertions expressed as comments: the effect of a false assertion is highly visible (the program terminates with an error message). The </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">assert</font><font face="Times New Roman, Times, Serif" size="3"> function is therefore valuable in software testing. A program under development might be filled with calls to the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">assert</font><font face="Times New Roman, Times, Serif" size="3"> function to help identify where errors are occurring. If an assertion is false, the error message gives the precise line number of the failed assertion.</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">Additionally, there is a way to remove the assertions without really removing them. If you use the preprocessor directive #define NDEBUG before including the header file </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">assert.h</font><font face="Times New Roman, Times, Serif" size="3">, like this:</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">#define聽NDEBUG<br />#include聽<assert.h><br />.<br />.<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">then all calls to the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">assert</font><font face="Times New Roman, Times, Serif" size="3"> function are ignored when you run the program. (</font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">NDEBUG</font><font face="Times New Roman, Times, Serif" size="3"> stands for No debug, and a </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">#define</font><font face="Times New Roman, Times, Serif" size="3"> directive is a preprocessor feature that we don't discuss right now.) During program testing and debugging, programmers often like to turn off debugging statements yet leave them physically present in the source code in case they need the statements later. Inserting the line </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">#define</font><font face="Times New Roman, Times, Serif" size="3"></font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">NDEBUG</font><font face="Times New Roman, Times, Serif" size="3"> turns off assertion checking without having to remove the assertions.</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">As useful as the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">assert</font><font face="Times New Roman, Times, Serif" size="3"> function is, it has two limitations. First, the parameter to the function must be expressed as a C++ logical expression. We can turn the comment</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">//聽0.0聽<=聽deptSales聽<=聽25000.0</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">into an executable assertion with the 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">assert(0.0聽<=聽deptSales聽&&聽deptSales聽<=聽25000.0);</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">But there is no easy way to turn the comment</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">//聽For聽each聽department,聽the聽file聽contains聽a聽department聽ID,<br />//聽number聽of聽days,聽and聽one聽sales聽figure聽for聽each聽day</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_371.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_372</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_373.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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