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📁 linux下一些常用的C函数的说明和例子
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<head>
<title>Untitled Document</title>
</head>
<body>
<table width="100%">
<tr> 
    <td width="80" valign="top">  
      <div align="right"><br>
        <font face='宋体' size='2'><a name=linuxc1></a></font> </div>
    </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> <br>
        </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> <br>
      isalnum(测试字符是否为英文或数字) </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 相关函数 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> isalpha,isdigit,islower,isupper<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 表头文件 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> #include&lt;ctype.h&gt;<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 定义函数 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> int isalnum (int c)<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 函数说明 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> 检查参数c是否为英文字母或阿拉伯数字,在标准c中相当于使用“isalpha(c) 
      || isdigit(c)”做测试。<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 返回值 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> 若参数c为字母或数字,则返回TRUE,否则返回NULL(0)。<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 附加说明 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> 此为宏定义,非真正函数。<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 范例 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> /* 找出str 字符串中为英文字母或数字的字符*/<br>
      #include &lt; ctype.h&gt;<br>
      main()<br>
      {<br>
      char str[]=”123c@#FDsP[e?”;<br>
      int i;<br>
      for (i=0;str[i]!=0;i++ )<br>
      if ( isalnum(str[i])) printf(“%c is an alphanumeric character\n”,str[i]);<br>
      }<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 执行 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> 1 is an apphabetic character<br>
      2 is an apphabetic character<br>
      3 is an apphabetic character<br>
      c is an apphabetic character<br>
      F is an apphabetic character<br>
      D is an apphabetic character<br>
      s is an apphabetic character<br>
      P is an apphabetic character<br>
      e is an apphabetic character<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top">  
      <div align="right"><br>
        <font face='宋体' size='2'><a name=linuxc2></a></font> </div>
    </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> <br>
        </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> <br>
      isalpha (测试字符是否为英文字母) </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 相关函数 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> isalnum,islower,isupper<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 表头文件 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> #include&lt;ctype.h&gt;<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 定义函数 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> int isalpha (int c)<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 函数说明 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> 检查参数c是否为英文字母,在标准c中相当于使用“isupper(c)||islower(c)”做测试。<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 返回值 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> 若参数c为英文字母,则返回TRUE,否则返回NULL(0)。<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 附加说明 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> 此为宏定义,非真正函数。<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 范例 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> /* 找出str 字符串中为英文字母的字符*/<br>
      #include &lt;ctype.h&gt;<br>
      main()<br>
      {<br>
      char str[]=”123c@#FDsP[e?”;<br>
      int i;<br>
      for (i=0;str[i]!=0;i++)<br>
      if(isalpha(str[i])) printf(“%c is an alphanumeric character\n”,str[i]);<br>
      }<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 执行 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> c is an apphabetic character<br>
      F is an apphabetic character<br>
      D is an apphabetic character<br>
      s is an apphabetic character<br>
      P is an apphabetic character<br>
      e is an apphabetic character<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top">  
      <div align="right"><br>
        <font face='宋体' size='2'><a name=linuxc3></a></font> </div>
    </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> <br>
        </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> <br>
      isascii(测试字符是否为ASCII 码字符) </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 相关函数 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> iscntrl<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 表头文件 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> #include &lt;ctype.h&gt;<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 定义函数 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> int isascii(int c);<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 函数说明 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> 检查参数c是否为ASCII码字符,也就是判断c的范围是否在0到127之间。<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 返回值 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> 若参数c为ASCII码字符,则返回TRUE,否则返回NULL(0)。<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 附加说明 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> 此为宏定义,非真正函数。<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 范例 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> /* 判断int i是否具有对映的ASCII码字符*/<br>
      #include&lt;ctype.h&gt;<br>
      main()<br>
      {<br>
      int i;<br>
      for(i=125;i&lt;130;i++)<br>
      if(isascii(i))<br>
      printf("%d is an ascii character:%c\n",i,i);<br>
      else<br>
      printf("%d is not an ascii character\n",i);<br>
      }<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 执行 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> 125 is an ascii character:}<br>
      126 is an ascii character:~<br>
      127 is an ascii character:<br>
      128 is not an ascii character<br>
      129 is not an ascii character<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top">  
      <div align="right"><br>
        <font face='宋体' size='2'><a name=linuxc4></a></font> </div>
    </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> <br>
        </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> <br>
      iscntrl(测试字符是否为ASCII 码的控制字符) </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 相关函数 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> isascii<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 表头文件 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> #include &lt;ctype.h&gt;<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 定义函数 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> int iscntrl(int c);<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 函数说明 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> 检查参数c是否为ASCII控制码,也就是判断c的范围是否在0到30之间。<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 返回值 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> 若参数c为ASCII控制码,则返回TRUE,否则返回NULL(0)。<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 
      <div align="right"><font face='宋体' size='2'> 附加说明 </font> </div>
    </td>
    <td valign="top"> <font face='宋体' size='2'> 此为宏定义,非真正函数。<br>
      </font> </td>
  </tr>
  <tr> 
    <td width="80" valign="top">  
      <div align="right"><br>
        <font face='宋体' size='2'><a name=linuxc5></a></font> </div>
    </td>
  </tr>
  <tr> 
    <td width="80" valign="top"> 

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