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Ref-docs/c_lib_guide/2.2.html
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Ref-docs/c_lib_guide/2.2.html
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<html>
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<head>
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<title>
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C Guide--2.2 ctype.h
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</title>
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<!-- Changed by: eric huss, 12-Mar-1997 -->
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</head>
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<body text="#000000" bgcolor="#FFFFFF">
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<center>
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<table border=0 width=100%>
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<tr>
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<td align=left width=20% valign=top>
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<a href="2.1.html">
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<img src="left.gif" border=0>
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Previous Section<br>
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2.1 assert.h</a></td>
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<td align=center width=60% valign=top>
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| <a href="index.html">Table of Contents</a> |
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<a href="index2.html">Index</a> |</td>
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<td align=right width=20% valign=top>
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<a href="2.3.html">
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Next Section
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<img src="right.gif" border=0><br>
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2.3 errno.h</a></td>
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</tr>
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</table>
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</center>
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<hr>
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<h1>2.2 ctype.h</h1>
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<p>
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The ctype header is used for testing and converting characters. A control character refers
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to a character that is not part of the normal printing set. In the ASCII character set, the control
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characters are the characters from 0 (NUL) through 0x1F (US), and the character 0x7F (DEL).
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Printable characters are those from 0x20 (space) to 0x7E (tilde).
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<p>
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Functions:
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<blockquote><code><b>
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isalnum();<br>
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isalpha();<br>
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iscntrl();<br>
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isdigit();<br>
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isgraph();<br>
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islower();<br>
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isprint();<br>
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ispunct();<br>
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isspace();<br>
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isupper();<br>
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isxdigit();<br>
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tolower();<br>
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toupper();<br>
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</b></code></blockquote>
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<a name="is"></a>
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<h2>2.2.1 is... Functions</h2>
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<p>
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Declarations:
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<blockquote><code><b>
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int isalnum(int</b></code> <i>character</i><code><b>);<br>
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int isalpha(int</b></code> <i>character</i><code><b>);<br>
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int iscntrl(int</b></code> <i>character</i><code><b>);<br>
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int isdigit(int</b></code> <i>character</i><code><b>);<br>
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int isgraph(int</b></code> <i>character</i><code><b>);<br>
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int islower(int</b></code> <i>character</i><code><b>);<br>
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int isprint(int</b></code> <i>character</i><code><b>);<br>
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int ispunct(int</b></code> <i>character</i><code><b>);<br>
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int isspace(int</b></code> <i>character</i><code><b>);<br>
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int isupper(int</b></code> <i>character</i><code><b>);<br>
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int isxdigit(int</b></code><i> character</i><code><b>);<br>
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</b></code></blockquote>
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The is... functions test the given character and return a nonzero (true) result if it satisfies
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the following conditions. If not, then 0 (false) is returned.
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<p>
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Conditions:
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<table border=0>
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<tr>
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<td valign=top><code><b>isalnum</b></code></td>
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<td>a letter (A to Z or a to z) or a digit (0 to 9)</td>
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</tr>
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<tr>
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<td valign=top><code><b>isalpha</b></code></td>
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<td valign=top>a letter (A to Z or a to z)</td>
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</tr>
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<tr>
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<td valign=top><code><b>iscntrl</b></code></td>
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<td valign=top>any control character (0x00 to 0x1F or 0x7F)</td>
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</tr>
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<tr>
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<td valign=top><code><b>isdigit</b></code></td>
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<td valign=top>a digit (0 to 9)</td>
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</tr>
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<tr>
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<td valign=top><code><b>isgraph</b></code></td>
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<td valign=top>any printing character except for the space character (0x21 to 0x7E)</td>
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</tr>
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<tr>
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<td valign=top><code><b>islower</b></code></td>
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<td valign=top>a lowercase letter (a to z)</td>
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</tr>
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<tr>
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<td valign=top><code><b>isprint</b></code></td>
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<td valign=top>any printing character (0x20 to 0x7E)</td>
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</tr>
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<tr>
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<td valign=top><code><b>ispunct</b></code></td>
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<td valign=top>any punctuation character (any printing character except for space
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character or isalnum)</td>
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</tr>
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<tr>
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<td valign=top><code><b>isspace</b></code></td>
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<td valign=top>a whitespace character (space, tab, carriage return, new line, vertical tab,
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or formfeed)</td>
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</tr>
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<tr>
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<td valign=top><code><b>isupper</b></code></td>
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<td valign=top>an uppercase letter (A to Z)</td>
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</tr>
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<tr>
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<td valign=top><code><b>isxdigit</b></code></td>
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<td valign=top>a hexadecimal digit (0 to 9, A to F, or a to f)</td>
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</tr>
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</table>
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<a name="to"></a>
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<h2>2.2.2 to... Functions</h2>
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<p>
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Declarations:
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<blockquote><code><b>
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int tolower(int </b></code><i>character</i><code><b>);<br>
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int toupper(int </b></code><i>character</i><code><b>);<br>
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</b></code></blockquote>
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The to... functions provide a means to convert a single character. If the character
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matches the appropriate condition, then it is converted. Otherwise the character is returned
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unchanged.
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<p>
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Conditions:
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<table border=0>
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<tr>
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<td valign=top><code><b>tolower</b></code></td>
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<td valign=top>If the character is an uppercase character (A to Z), then it is converted to
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lowercase (a to z)</td>
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</tr>
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<tr>
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<td valign=top><code><b>toupper</b></code></td>
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<td valign=top>If the character is a lowercase character (a to z), then it is converted to
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uppercase (A to Z)</td>
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</tr>
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</table>
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Example:
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<blockquote><code><b><pre>
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#include<ctype.h>
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#include<stdio.h>
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#include<string.h>
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int main(void)
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{
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int loop;
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char string[]="THIS IS A TEST";
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for(loop=0;loop<strlen(string);loop++)
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string[loop]=tolower(string[loop]);
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printf("%s\n",string);
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return 0;
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}
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</pre></b></code></blockquote>
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<hr>
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<center>
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<table border=0 width=100%>
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<tr>
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<td align=left width=20% valign=top>
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<a href="2.1.html">
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||||
<img src="left.gif" border=0>
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Previous Section<br>
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2.1 assert.h</a></td>
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<td align=center width=60% valign=top>
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||||
| <a href="index.html">Table of Contents</a> |
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||||
<a href="index2.html">Index</a> |</td>
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<td align=right width=20% valign=top>
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<a href="2.3.html">
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||||
Next Section
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||||
<img src="right.gif" border=0><br>
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2.3 errno.h</a></td>
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</tr>
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</table>
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</center>
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</body>
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||||
</html>
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