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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_138</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_137.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_138</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_139.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 138</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"><i>(table continued from previous page)</i></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="509" cellpadding="7"><tr><td valign="top"><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="1"></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">cin聽>>聽x;</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">x</font><font face="Times New Roman, Times, Serif" size="2"> = 16.9</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">25\n<br />A\n<br />16.9<img src="c87ad29ccb4c3043fda0d0a93a820a4a.gif" border="0" alt="slashn.gif" width="21" height="17" /></font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">3.</font></td><td valign="top"></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2"><img src="ec078373e441125867c02332d6dea8c0.gif" border="0" alt="two.gif" width="13" height="15" /> 5A16.9\n</font></td></tr><tr><td valign="top"><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="1"></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">cin</font><font face="Times New Roman, Times, Serif" size="2"> >> </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">i;</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">i</font><font face="Times New Roman, Times, Serif" size="2"> = 25</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">25<img src="1c9eff0a24c07a6c21609e9186b427f5.gif" border="0" alt="a.gif" width="15" height="16" /> 16.9\n</font></td></tr><tr><td valign="top"><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="1"></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">cin</font><font face="Times New Roman, Times, Serif" size="2"> >> </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">ch;</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">ch</font><font face="Times New Roman, Times, Serif" size="2"> = A</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">25A<img src="d21d311830428cb6588f051002a8a417.gif" border="0" alt="one.gif" width="14" height="15" /> 6.9\n</font></td></tr><tr><td valign="top"><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="1"></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">cin</font><font face="Times New Roman, Times, Serif" size="2"> >> </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">x;</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td><td valign="top"><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">x</font><font face="Times New Roman, Times, Serif" size="2"> = 16.9</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">25A16.9<img src="c87ad29ccb4c3043fda0d0a93a820a4a.gif" border="0" alt="slashn.gif" width="21" height="17" /></font></td></tr></table></td></tr></table><br /><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"><i>Reading Character Data with the get Function</i></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 we have discussed, the >> operator skips any leading whitespace characters (such as blanks and newline characters) while looking for the next data value in the input stream. Suppose that </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">ch1</font><font face="Times New Roman, Times, Serif" size="3"> and </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">ch2</font><font face="Times New Roman, Times, Serif" size="3"> are </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">char</font><font face="Times New Roman, Times, Serif" size="3"> variables and the program executes 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">cin聽>>聽ch1聽>>聽ch2;</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">If the input stream consists of</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">R聽1</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 the extraction operator stores R into </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">chl</font><font face="Times New Roman, Times, Serif" size="3">, skips the blank, and stores 1 into </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">ch2</font><font face="Times New Roman, Times, Serif" size="3">. (Note that the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">char</font><font face="Times New Roman, Times, Serif" size="3"> value 1 is not the same as the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">int</font><font face="Times New Roman, Times, Serif" size="3"> value 1. The two are stored completely differently in a computer's memory. The extraction operator interprets the same data in different ways, depending on the data type of the variable that's being filled.)</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">What if we had wanted to input <i>three</i> characters from the input line: the <i>R,</i> the blank, and the 1? With the extraction operator, it's not possible. Whitespace characters such as blanks are skipped over.</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">The </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">istream</font><font face="Times New Roman, Times, Serif" size="3"> data type provides a second way in which to read character data, in addition to the >> operator. You can use the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">get</font><font face="Times New Roman, Times, Serif" size="3"> function, which inputs the very next character in the input stream without skipping any whitespace characters. A function call looks 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">cin.get(someChar)聽;</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">You give the name of an </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">istream</font><font face="Times New Roman, Times, Serif" size="3"> variable (here, </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">cin</font><font face="Times New Roman, Times, Serif" size="3">), then a dot (period), and then the function name and parameter list. Notice that the call to </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">get</font><font face="Times New Roman, Times, Serif" size="3"> uses</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_137.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_138</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_139.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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