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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_677</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_676.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_677</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_678.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 677</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">The </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">strcpy</font><font face="Times New Roman, Times, Serif" size="3"> routine is important because aggregate assignment with the </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">=</font><font face="Times New Roman, Times, Serif" size="3"> operator is not allowed. In the following code fragment, we show the wrong way and the right way to perform a string copy.</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><br />聽聽.<br />聽聽.<br />聽聽.<br />char聽myStr[100];<br />聽聽.<br />聽聽.<br />聽聽.<br />myStr聽=聽"Abracadabra";聽聽聽聽聽聽聽聽聽聽//聽No<br />strcpy(myStr,聽"Abracadabra");聽聽聽//聽Yes</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">In </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">strcpy's</font><font face="Times New Roman, Times, Serif" size="3"> parameter list, the destination string is the one on the left, just as an assignment operation transfers data from right to left. It is the caller's responsibility to make sure that the destination array is large enough to hold the result.</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">strcpy</font><font face="Times New Roman, Times, Serif" size="3"> function is technically a value-returning function; it not only copies one string to another, it also returns as a function value the base address of the destination array. The reason why the caller would want to use this function value is not at all obvious, and we don't discuss it here. Programmers nearly always ignore the function value and simply invoke </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">strcpy</font><font face="Times New Roman, Times, Serif" size="3"> as if it were a void function (as we did above). You may wish to review the Background Information box in Chapter 8 entitled "Ignoring a Function Value."</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">strcmp</font><font face="Times New Roman, Times, Serif" size="3"> function is used for comparing two strings. The function receives two strings as parameters and compares them in <i>lexicographic</i> order (the order in which they would appear in a dictionary). Specifically, corresponding characters in the strings are compared one by one, starting with the first. The first unequal pair of characters determines the order. For example, "Hello" compares less than "Helvetica". The first three characters are the same in both strings, but 'l' compares less than 'v' in both ASCII and EBCDIC. Given the function call </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">strcmp (str1</font><font face="Times New Roman, Times, Serif" size="3">, </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">str2</font><font face="Times New Roman, Times, Serif" size="3">), the function returns one of the following </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">int</font><font face="Times New Roman, Times, Serif" size="3"> values: a negative integer, if </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">str1 < str2</font><font face="Times New Roman, Times, Serif" size="3"> lexicographically; the value 0, if </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">str1 = str2;</font><font face="Times New Roman, Times, Serif" size="3"> or a positive integer, if </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">str1 > str2</font><font face="Times New Roman, Times, Serif" size="3">. The precise values of the negative integer and the positive integer are unspecified. You simply test to see if the result is less than zero, zero, or greater than zero. Here is an example:</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">if聽(strcmp(str1,聽str2)聽<聽0)聽聽聽聽//聽If聽strl聽is聽less聽than聽str2聽...<br />聽聽.<br />聽聽.<br />聽聽.</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">Given the declarations</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_676.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_677</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_678.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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