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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_981</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_980.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_981</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_982.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 981</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">out of space available for dynamic data, the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">new</font><font face="Times New Roman, Times, Serif" size="3"> operator returns the null pointer.</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">Variables created by </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">new</font><font face="Times New Roman, Times, Serif" size="3"> are said to be on the free store (or heap), a region of memory set aside for dynamic variables. The </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">new</font><font face="Times New Roman, Times, Serif" size="3"> operator obtains a chunk of memory from the free store and, as we will see, the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">delete</font><font face="Times New Roman, Times, Serif" size="3"> operator returns it to the free store.</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" 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">Free Store (Heap) A pool of memory locations reserved for allocation and deallocation of dynamic data.</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">A dynamic variable is unnamed and cannot be directly addressed. It must be indirectly addressed through the pointer returned by the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">new</font><font face="Times New Roman, Times, Serif" size="3"> operator. Below is an example of creating dynamic data and then accessing the data through pointers. The code begins by initializing the pointer variables in their declarations.</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">#include聽<string.h>聽聽聽//聽For聽strcpy()<br />聽聽.<br />聽聽.<br />聽聽.<br />int*聽聽intPtr聽=聽new聽int;<br />char*聽nameStr聽=聽new聽char[6];<br /><br />*intPtr聽=聽357;<br />strcpy(nameStr,聽Ben);</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">Recall from Chapter 12 that the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">strcpy</font><font face="Times New Roman, Times, Serif" size="3"> library function requires two parameters, each being the base address of a </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">char</font><font face="Times New Roman, Times, Serif" size="3"> array. For the first parameter, we are passing the base address of the dynamic array on the free store. For the second parameter, the compiler passes the base address of the anonymous array where the string Ben (including the terminating null character) is located. Figures 17-6a and 17-6b picture the effect of executing this code segment.</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">Dynamic data can be destroyed at any time during the execution of a program when it is no longer needed. The built-in operator </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">delete</font><font face="Times New Roman, Times, Serif" size="3"> is used to destroy a dynamic variable. The </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">delete</font><font face="Times New Roman, Times, Serif" size="3"> operation has two forms, one for deleting a single variable, the other for deleting an 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="Times New Roman, Times, Serif" size="3"><img src="7bdc277810e3bfc07ad6c5774cad1fd9.gif" border="0" alt="0981-01.gif" width="161" height="86" /></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_980.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_981</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_982.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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