ISALPHA(3) Linux Programmer's Manual ISALPHA(3)
NAME
 isalnum, 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, is-
 print_l, ispunct_l, isspace_l, isupper_l, isxdigit_l - character clas-
 sification functions
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 since 2.19: */ _DEFAULT_SOURCE
 || /* Glibc versions <= 2.19: */ _SVID_SOURCE
 isblank():
 _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
 isalnum_l(), isalpha_l(), isblank_l(), iscntrl_l(), isdigit_l(), is-
 graph_l(), islower_l(), isprint_l(), ispunct_l(), isspace_l(), isup-
 per_l(), isxdigit_l():
 Since glibc 2.10:
 _XOPEN_SOURCE >= 700
 Before glibc 2.10:
 _GNU_SOURCE
 isascii_l():
 Since glibc 2.10:
 _XOPEN_SOURCE >= 700 && (_SVID_SOURCE || _BSD_SOURCE)
 Before glibc 2.10:
 _GNU_SOURCE
DESCRIPTION
 These functions check whether c, which must have the value of an un-
 signed 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 lo-
 cale 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 lo-
 cale object locale instead of the current locale.
 isalnum()
 checks for an alphanumeric character; it is equivalent to (isal-
 pha(c) || isdigit(c)).
 isalpha()
 checks for an alphabetic character; in the standard "C" locale,
 it is equivalent to (isupper(c) || islower(c)). In some lo-
 cales, 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" lo-
 cales, these are: space, form-feed ('\f'), newline ('\n'), car-
 riage 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 VALUE
 The values returned are nonzero if the character c falls into the
 tested class, and zero if not.
VERSIONS
 isalnum_l(), isalpha_l(), isblank_l(), iscntrl_l(), isdigit_l(), is-
 graph_l(), islower_l(), isprint_l(), ispunct_l(), isspace_l(), isup-
 per_l(), isxdigit_l(), and isascii_l() are available since glibc 2.3.
ATTRIBUTES
 For an explanation of the terms used in this section, see at-
 tributes(7).
 +---------------------------------+---------------+---------+
 |Interface | Attribute | Value |
 +---------------------------------+---------------+---------+
 |isalnum(), isalpha(), isascii(), | Thread safety | MT-Safe |
 |isblank(), iscntrl(), isdigit(), | | |
 |isgraph(), islower(), isprint(), | | |
 |ispunct(), isspace(), isupper(), | | |
 |isxdigit() | | |
 +---------------------------------+---------------+---------+
CONFORMING TO
 C89 specifies isalnum(), isalpha(), iscntrl(), isdigit(), isgraph(),
 islower(), isprint(), ispunct(), isspace(), isupper(), and isxdigit(),
 but not isascii() and isblank(). POSIX.1-2001 also specifies those
 functions, and also isascii() (as an XSI extension) and isblank(). 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(), iscn-
 trl_l(), isdigit_l(), isgraph_l(), islower_l(), isprint_l(), is-
 punct_l(), isspace_l(), isupper_l(), and isxdigit_l().
 isascii_l() is a GNU extension.
NOTES
 The 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 un-
 signed char.
 The details of what characters belong to which class depend on the lo-
 cale. For example, isupper() will not recognize an A-umlaut (A) as an
 uppercase letter in the default C locale.
SEE ALSO
 iswalnum(3), iswalpha(3), iswblank(3), iswcntrl(3), iswdigit(3), isw-
 graph(3), iswlower(3), iswprint(3), iswpunct(3), iswspace(3), iswup-
 per(3), iswxdigit(3), newlocale(3), setlocale(3), toascii(3),
 tolower(3), toupper(3), uselocale(3), ascii(7), locale(7)
COLOPHON
 This page is part of release 5.10 of the Linux man-pages project. A
 description of the project, information about reporting bugs, and the
 latest version of this page, can be found at
 https://www.kernel.org/doc/man-pages/.
GNU 2017年09月15日 ISALPHA(3)