Section : 3 Updated : 2023-02-05 Source : Linux man-pages 6.03 NAMEisalnum, isalpha, isascii, isblank, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, isxdigit, isalnum_l, isalpha_l, isascii_l, isblank_l, iscntrl_l, isdigit_l, isgraph_l, islower_l, isprint_l, ispunct_l, isspace_l, isupper_l, isxdigit_l − character classification functions LIBRARYStandard C library (libc, −lc)SYNOPSIS#include <ctype.h>int isalnum(int c);
int isalpha(int c);
int iscntrl(int c);
int isdigit(int c);
int isgraph(int c);
int islower(int c);
int isprint(int c);
int ispunct(int c);
int isspace(int c);
int isupper(int c);
int isxdigit(int c);int isascii(int c);
int isblank(int c);int isalnum_l(int c, locale_t locale);
int isalpha_l(int c, locale_t locale);
int isblank_l(int c, locale_t locale);
int iscntrl_l(int c, locale_t locale);
int isdigit_l(int c, locale_t locale);
int isgraph_l(int c, locale_t locale);
int islower_l(int c, locale_t locale);
int isprint_l(int c, locale_t locale);
int ispunct_l(int c, locale_t locale);
int isspace_l(int c, locale_t locale);
int isupper_l(int c, locale_t locale);
int isxdigit_l(int c, locale_t locale);int isascii_l(int c, locale_t locale);Feature Test Macro Requirements for glibc (see feature_test_macros(7)):isascii(): _XOPEN_SOURCE
|| /* glibc >= 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _SVID_SOURCEisblank(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112Lisalnum_l(),isalpha_l(),isblank_l(),iscntrl_l(),isdigit_l(),isgraph_l(),islower_l(),isprint_l(),ispunct_l(),isspace_l(),isupper_l(),isxdigit_l(): Since glibc 2.10:
_XOPEN_SOURCE >= 700
Before glibc 2.10:
_GNU_SOURCEisascii_l(): Since glibc 2.10:
_XOPEN_SOURCE >= 700 && (_SVID_SOURCE || _BSD_SOURCE)
Before glibc 2.10:
_GNU_SOURCEDESCRIPTIONThese functions check whether c, which must have the value of an unsigned char or EOF, falls into a certain character class according to the specified locale. The functions without the "_l" suffix perform the check based on the current locale. The functions with the "_l" suffix perform the check based on the locale specified by the locale object locale. The behavior of these functions is undefined if locale is the special locale object LC_GLOBAL_LOCALE (see duplocale(3)) or is not a valid locale object handle. The list below explains the operation of the functions without the "_l" suffix; the functions with the "_l" suffix differ only in using the locale object locale instead of the current locale. isalnum()checks for an alphanumeric character; it is equivalent to (isalpha(c) || isdigit(c)).isalpha()checks for an alphabetic character; in the standard "C" locale, it is equivalent to (isupper(c) || islower(c)). In some locales, there may be additional characters for which isalpha() is true—letters which are neither uppercase nor lowercase. isascii()checks whether c is a 7-bit unsigned char value that fits into the ASCII character set. isblank()checks for a blank character; that is, a space or a tab. iscntrl()checks for a control character. isdigit()checks for a digit (0 through 9). isgraph()checks for any printable character except space. islower()checks for a lowercase character. isprint()checks for any printable character including space. ispunct()checks for any printable character which is not a space or an alphanumeric character. isspace()checks for white-space characters. In the """C"""and """POSIX"""locales, these are: space, form-feed ('\f'), newline ('\n'), carriage return ('\r'), horizontal tab ('\t'), and vertical tab ('\v').isupper()checks for an uppercase letter. isxdigit()checks for hexadecimal digits, that is, one of 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F.RETURN VALUEThe values returned are nonzero if the character c falls into the tested class, and zero if not. VERSIONSisalnum_l(),isalpha_l(),isblank_l(),iscntrl_l(),isdigit_l(),isgraph_l(),islower_l(),isprint_l(),ispunct_l(),isspace_l(),isupper_l(),isxdigit_l(), and isascii_l() are available since glibc 2.3. ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
STANDARDSPOSIX.1-2001 specifies isalnum(),isalpha(),isblank(),iscntrl(),isdigit(),isgraph(),islower(),isprint(),ispunct(),isspace(),isupper(), and isxdigit(), and also isascii()(as an XSI extension). C99 specifies all of the preceding functions, except isascii().POSIX.1-2008 marks isascii() as obsolete, noting that it cannot be used portably in a localized application. POSIX.1-2008 specifies isalnum_l(),isalpha_l(),isblank_l(),iscntrl_l(),isdigit_l(),isgraph_l(),islower_l(),isprint_l(),ispunct_l(),isspace_l(),isupper_l(), and isxdigit_l().isascii_l() is a GNU extension. NOTESThe standards require that the argument c for these functions is either EOF or a value that is representable in the type unsigned char. If the argument c is of type char, it must be cast to unsigned char, as in the following example: char c;
...
res = toupper((unsigned char) c);This is necessary because char may be the equivalent of signed char, in which case a byte where the top bit is set would be sign extended when converting to int, yielding a value that is outside the range of unsigned char.The details of what characters belong to which class depend on the locale. For example, isupper() will not recognize an A-umlaut (Ä) as an uppercase letter in the default C"locale. SEE ALSOiswalnum(3),iswalpha(3),iswblank(3),iswcntrl(3),iswdigit(3),iswgraph(3),iswlower(3),iswprint(3),iswpunct(3),iswspace(3),iswupper(3),iswxdigit(3),newlocale(3),setlocale(3),toascii(3),tolower(3),toupper(3),uselocale(3),ascii(7),locale(7)0 Johanes Gumabo Data Size : 35,817 byte man-isblank.3Build : 2025-03-22, 13:26 : Visitor Screen : x Visitor Counter ( page / site ) : 30 / 2,230,589 Visitor ID : : Visitor IP : 216.73.216.247 : Visitor Provider : AMAZON-02 : Provider Position ( lat x lon ) : 39.962500 x -83.006100 : x Provider Accuracy Radius ( km ) : 20 : Provider City : Columbus : Provider Province : Ohio , : , Provider Country : United States : Provider Continent : North America : Visitor Recorder : Version : Visitor Recorder : Library : Online Linux Manual Page : Version : Online Linux Manual Page - Fedora.40 - march=x86-64 - mtune=generic - 25.03.22 Online Linux Manual Page : Library : lib_c - 24.10.03 - march=x86-64 - mtune=generic - Fedora.40 Online Linux Manual Page : Library : lib_m - 24.10.03 - march=x86-64 - mtune=generic - Fedora.40 Data Base : Version : Online Linux Manual Page Database - 24.04.13 - march=x86-64 - mtune=generic - fedora-38 Data Base : Library : lib_c - 23.02.07 - march=x86-64 - mtune=generic - fedora.36
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