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<p class="MsoNormal"><span lang="EN-US"><a href="file:///C:/Documents%20and%20Settings/ZS/桌面/index.html">cppreference.com</a>
-> <a href="file:///C:/Documents%20and%20Settings/ZS/桌面/stdstring.html">Standard
C String & Character</a> -> </span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">详解</span><span lang="EN-US" style="FONT-SIZE: 12pt; FONT-FAMILY: 宋体"><o:p>
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<h1>标准<span lang="EN-US">c字符和字符串</span></h1>
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<h2><span lang="EN-US"><a name="atof">atof</a></span></h2>
<p class="MsoNormal"><i><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">语法</span><span lang="EN-US">:</span></i></p>
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<pre><span lang="EN-US"> <o:p>
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<pre><span lang="EN-US"><span style="mso-spacerun: yes"> </span>#include <stdlib.h></span></pre>
<pre><span lang="EN-US"><span style="mso-spacerun: yes"> </span>double atof( const char *str );</span></pre>
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<p>功能<span lang="EN-US">:将字符串<i>str</i>转换成一个双精度数值并返回结果。
参数<i>str</i> 必须以有效数字开头,但是允许以“E”或“e”除外的任意非数字字符结尾。例如：</span></p>
<pre><span lang="EN-US"><span style="mso-spacerun: yes"> </span>x = atof( "42.0is_the_answer" );</span></pre>
<p style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt"><span lang="EN-US">x的值为42.0.</span></p>
<p class="MsoNormal" style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt"><i><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">相关主题</span><span lang="EN-US">:</span></i><span lang="EN-US"><br>
<strong><a href="#atoi">atoi()</a> and <a href="#atol">atol()</a>.</strong></span></p>
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<h2 style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt"><span lang="EN-US">
<a name="atoi">atoi</a></span></h2>
<p class="MsoNormal" style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt"><i><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">语法</span><span lang="EN-US">:</span></i></p>
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<pre><span lang="EN-US"> <o:p>
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<pre><span lang="EN-US"><span style="mso-spacerun: yes"> </span>#include <stdlib.h></span></pre>
<pre><span lang="EN-US"><span style="mso-spacerun: yes"> </span>int atoi( const char *str );</span></pre>
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<p style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt">功能：将字符串<i><span lang="EN-US">str</span></i>转换成一个整数并返回结果。参数<i><span lang="EN-US">str</span></i><span lang="EN-US">
以数字开头，当函数从<i>str</i>
中读到非数字字符则结束转换并将结果返回。例如，</span></p>
<pre><span lang="EN-US"><span style="mso-spacerun: yes"> </span>i = atoi( "512.035" );</span></pre>
<p style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt"><span lang="EN-US">i
的值为 512.</span></p>
<p class="MsoNormal" style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt"><i><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">相关主题</span><span lang="EN-US">:</span></i><span lang="EN-US"><br>
<strong><a href="#atof">atof()</a> and <a href="#atol">atol()</a>.</strong></span></p>
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<h2 style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt"><span lang="EN-US">
<a name="atol">atol</a></span></h2>
<p class="MsoNormal" style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt"><i><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">语法</span><span lang="EN-US">:</span></i></p>
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<pre><span lang="EN-US"> <o:p>
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<pre><span lang="EN-US"> <span style="mso-spacerun: yes"> </span>#include <stdlib.h></span></pre>
<pre><span lang="EN-US"><span style="mso-spacerun: yes"> </span>long atol( const char *str );</span></pre>
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<p style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt">功能：将字符串转换成长整型数并返回结果。函数会扫描参数<i><span lang="EN-US">str</span></i>字符串，跳过前面的空格字符，直到遇上数字或正负符号才开始做转换，而再遇到非数字或字符串结束时才结束转换，并将结果返回。例如，</p>
<pre><span lang="EN-US"><span style="mso-spacerun: yes"> </span>x = atol( "1024.0001" );</span></pre>
<p style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt"><span lang="EN-US">x的值为1024L.</span></p>
<p class="MsoNormal" style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt"><i><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">相关主题</span><span lang="EN-US">:</span></i><span lang="EN-US"><br>
<strong><a href="#atof">atof()</a> and <a href="#atoi">atoi()</a>.</strong></span></p>
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<a name="isalnum">isalnum</a></span></h2>
<p class="MsoNormal" style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt"><i><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">语法</span><span lang="EN-US">:</span></i></p>
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<pre><span lang="EN-US"> <o:p>
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<pre><span lang="EN-US"><span style="mso-spacerun: yes"> </span>#include <ctype.h></span></pre>
<pre><span lang="EN-US"><span style="mso-spacerun: yes"> </span>int isalnum( int ch );</span></pre>
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<p style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt">功能：如果参数是数字或字母字符，函数返回非零值，否则返回零值。</p>
<pre><span lang="EN-US"><span style="mso-spacerun: yes"> </span>char c;</span></pre>
<pre><span lang="EN-US"><span style="mso-spacerun: yes"> </span>scanf( "%c", &c );</span></pre>
<pre><span lang="EN-US"><span style="mso-spacerun: yes"> </span>if( isalnum(c) )</span></pre>
<pre><span lang="EN-US"><span style="mso-spacerun: yes"> </span>printf( "You entered the alphanumeric character %c\n", c );</span></pre>
<p class="MsoNormal" style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt"><i><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">相关主题</span><span lang="EN-US">:</span></i><span lang="EN-US"><br>
<strong><a href="#isalpha">isalpha()</a>, <a href="#iscntrl">iscntrl()</a>, <a href="#isdigit">isdigit()</a>,
<a href="#isgraph">isgraph()</a>, <a href="#isprint">isprint()</a>, <a href="#ispunct">ispunct()</a>,
and <a href="#isspace">isspace()</a>.</strong></span></p>
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<h2 style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt"><span lang="EN-US">
<a name="isalpha">isalpha</a></span></h2>
<p class="MsoNormal" style="tab-stops: 45.8pt 91.6pt 137.4pt 183.2pt 229.0pt 274.8pt 320.6pt 366.4pt 412.2pt 458.0pt 503.8pt 549.6pt 595.4pt 641.2pt 687.0pt 732.8pt"><i><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">语法</span><span lang="EN-US">:</span></i></p>
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<pre><span lang="EN-US"> <o:p>
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