| <html lang="en"> |
| <head> |
| <title>Classification of Characters - The GNU C Library</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="The GNU C Library"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="Character-Handling.html#Character-Handling" title="Character Handling"> |
| <link rel="next" href="Case-Conversion.html#Case-Conversion" title="Case Conversion"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| This file documents the GNU C library. |
| |
| This is Edition 0.12, last updated 2007-10-27, |
| of `The GNU C Library Reference Manual', for version |
| 2.8 (Sourcery G++ Lite 2011.03-41). |
| |
| Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002, |
| 2003, 2007, 2008, 2010 Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being ``Free Software Needs Free Documentation'' |
| and ``GNU Lesser General Public License'', the Front-Cover texts being |
| ``A GNU Manual'', and with the Back-Cover Texts as in (a) below. A |
| copy of the license is included in the section entitled "GNU Free |
| Documentation License". |
| |
| (a) The FSF's Back-Cover Text is: ``You have the freedom to |
| copy and modify this GNU manual. Buying copies from the FSF |
| supports it in developing GNU and promoting software freedom.''--> |
| <meta http-equiv="Content-Style-Type" content="text/css"> |
| <style type="text/css"><!-- |
| pre.display { font-family:inherit } |
| pre.format { font-family:inherit } |
| pre.smalldisplay { font-family:inherit; font-size:smaller } |
| pre.smallformat { font-family:inherit; font-size:smaller } |
| pre.smallexample { font-size:smaller } |
| pre.smalllisp { font-size:smaller } |
| span.sc { font-variant:small-caps } |
| span.roman { font-family:serif; font-weight:normal; } |
| span.sansserif { font-family:sans-serif; font-weight:normal; } |
| --></style> |
| <link rel="stylesheet" type="text/css" href="../cs.css"> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="Classification-of-Characters"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="Case-Conversion.html#Case-Conversion">Case Conversion</a>, |
| Up: <a rel="up" accesskey="u" href="Character-Handling.html#Character-Handling">Character Handling</a> |
| <hr> |
| </div> |
| |
| <h3 class="section">4.1 Classification of Characters</h3> |
| |
| <p><a name="index-character-testing-364"></a><a name="index-classification-of-characters-365"></a><a name="index-predicates-on-characters-366"></a><a name="index-character-predicates-367"></a> |
| This section explains the library functions for classifying characters. |
| For example, <code>isalpha</code> is the function to test for an alphabetic |
| character. It takes one argument, the character to test, and returns a |
| nonzero integer if the character is alphabetic, and zero otherwise. You |
| would use it like this: |
| |
| <pre class="smallexample"> if (isalpha (c)) |
| printf ("The character `%c' is alphabetic.\n", c); |
| </pre> |
| <p>Each of the functions in this section tests for membership in a |
| particular class of characters; each has a name starting with ‘<samp><span class="samp">is</span></samp>’. |
| Each of them takes one argument, which is a character to test, and |
| returns an <code>int</code> which is treated as a boolean value. The |
| character argument is passed as an <code>int</code>, and it may be the |
| constant value <code>EOF</code> instead of a real character. |
| |
| <p>The attributes of any given character can vary between locales. |
| See <a href="Locales.html#Locales">Locales</a>, for more information on locales. |
| |
| <p>These functions are declared in the header file <samp><span class="file">ctype.h</span></samp>. |
| <a name="index-ctype_002eh-368"></a> |
| <a name="index-lower_002dcase-character-369"></a><!-- ctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>islower</b> (<var>int c</var>)<var><a name="index-islower-370"></a></var><br> |
| <blockquote><p>Returns true if <var>c</var> is a lower-case letter. The letter need not be |
| from the Latin alphabet, any alphabet representable is valid. |
| </p></blockquote></div> |
| |
| <p><a name="index-upper_002dcase-character-371"></a><!-- ctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>isupper</b> (<var>int c</var>)<var><a name="index-isupper-372"></a></var><br> |
| <blockquote><p>Returns true if <var>c</var> is an upper-case letter. The letter need not be |
| from the Latin alphabet, any alphabet representable is valid. |
| </p></blockquote></div> |
| |
| <p><a name="index-alphabetic-character-373"></a><!-- ctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>isalpha</b> (<var>int c</var>)<var><a name="index-isalpha-374"></a></var><br> |
| <blockquote><p>Returns true if <var>c</var> is an alphabetic character (a letter). If |
| <code>islower</code> or <code>isupper</code> is true of a character, then |
| <code>isalpha</code> is also true. |
| |
| <p>In some locales, there may be additional characters for which |
| <code>isalpha</code> is true—letters which are neither upper case nor lower |
| case. But in the standard <code>"C"</code> locale, there are no such |
| additional characters. |
| </p></blockquote></div> |
| |
| <p><a name="index-digit-character-375"></a><a name="index-decimal-digit-character-376"></a><!-- ctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>isdigit</b> (<var>int c</var>)<var><a name="index-isdigit-377"></a></var><br> |
| <blockquote><p>Returns true if <var>c</var> is a decimal digit (‘<samp><span class="samp">0</span></samp>’ through ‘<samp><span class="samp">9</span></samp>’). |
| </p></blockquote></div> |
| |
| <p><a name="index-alphanumeric-character-378"></a><!-- ctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>isalnum</b> (<var>int c</var>)<var><a name="index-isalnum-379"></a></var><br> |
| <blockquote><p>Returns true if <var>c</var> is an alphanumeric character (a letter or |
| number); in other words, if either <code>isalpha</code> or <code>isdigit</code> is |
| true of a character, then <code>isalnum</code> is also true. |
| </p></blockquote></div> |
| |
| <p><a name="index-hexadecimal-digit-character-380"></a><!-- ctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>isxdigit</b> (<var>int c</var>)<var><a name="index-isxdigit-381"></a></var><br> |
| <blockquote><p>Returns true if <var>c</var> is a hexadecimal digit. |
| Hexadecimal digits include the normal decimal digits ‘<samp><span class="samp">0</span></samp>’ through |
| ‘<samp><span class="samp">9</span></samp>’ and the letters ‘<samp><span class="samp">A</span></samp>’ through ‘<samp><span class="samp">F</span></samp>’ and |
| ‘<samp><span class="samp">a</span></samp>’ through ‘<samp><span class="samp">f</span></samp>’. |
| </p></blockquote></div> |
| |
| <p><a name="index-punctuation-character-382"></a><!-- ctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>ispunct</b> (<var>int c</var>)<var><a name="index-ispunct-383"></a></var><br> |
| <blockquote><p>Returns true if <var>c</var> is a punctuation character. |
| This means any printing character that is not alphanumeric or a space |
| character. |
| </p></blockquote></div> |
| |
| <p><a name="index-whitespace-character-384"></a><!-- ctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>isspace</b> (<var>int c</var>)<var><a name="index-isspace-385"></a></var><br> |
| <blockquote><p>Returns true if <var>c</var> is a <dfn>whitespace</dfn> character. In the standard |
| <code>"C"</code> locale, <code>isspace</code> returns true for only the standard |
| whitespace characters: |
| |
| <dl> |
| <dt><code>' '</code><dd>space |
| |
| <br><dt><code>'\f'</code><dd>formfeed |
| |
| <br><dt><code>'\n'</code><dd>newline |
| |
| <br><dt><code>'\r'</code><dd>carriage return |
| |
| <br><dt><code>'\t'</code><dd>horizontal tab |
| |
| <br><dt><code>'\v'</code><dd>vertical tab |
| </dl> |
| </p></blockquote></div> |
| |
| <p><a name="index-blank-character-386"></a><!-- ctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>isblank</b> (<var>int c</var>)<var><a name="index-isblank-387"></a></var><br> |
| <blockquote><p>Returns true if <var>c</var> is a blank character; that is, a space or a tab. |
| This function was originally a GNU extension, but was added in ISO C99<!-- /@w -->. |
| </p></blockquote></div> |
| |
| <p><a name="index-graphic-character-388"></a><!-- ctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>isgraph</b> (<var>int c</var>)<var><a name="index-isgraph-389"></a></var><br> |
| <blockquote><p>Returns true if <var>c</var> is a graphic character; that is, a character |
| that has a glyph associated with it. The whitespace characters are not |
| considered graphic. |
| </p></blockquote></div> |
| |
| <p><a name="index-printing-character-390"></a><!-- ctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>isprint</b> (<var>int c</var>)<var><a name="index-isprint-391"></a></var><br> |
| <blockquote><p>Returns true if <var>c</var> is a printing character. Printing characters |
| include all the graphic characters, plus the space (‘<samp> </samp>’) character. |
| </p></blockquote></div> |
| |
| <p><a name="index-control-character-392"></a><!-- ctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>iscntrl</b> (<var>int c</var>)<var><a name="index-iscntrl-393"></a></var><br> |
| <blockquote><p>Returns true if <var>c</var> is a control character (that is, a character that |
| is not a printing character). |
| </p></blockquote></div> |
| |
| <p><a name="index-ASCII-character-394"></a><!-- ctype.h --> |
| <!-- SVID, BSD --> |
| |
| <div class="defun"> |
| — Function: int <b>isascii</b> (<var>int c</var>)<var><a name="index-isascii-395"></a></var><br> |
| <blockquote><p>Returns true if <var>c</var> is a 7-bit <code>unsigned char</code> value that fits |
| into the US/UK ASCII character set. This function is a BSD extension |
| and is also an SVID extension. |
| </p></blockquote></div> |
| |
| </body></html> |
| |
