isalpha(3) - Linux manual page (original) (raw)
isalpha(3) Library Functions Manual isalpha(3)
NAME top
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, isprint_l, ispunct_l, isspace_l, isupper_l, isxdigit_l
- character classification functionsLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#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_SOURCE
**isblank**():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
**isalnum_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_SOURCE
**isascii_l**():
Since glibc 2.10:
_XOPEN_SOURCE >= 700 && (_SVID_SOURCE || _BSD_SOURCE)
Before glibc 2.10:
_GNU_SOURCEDESCRIPTION top
These 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)](../man3/duplocale.3.html)) 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 VALUE top
The values returned are nonzero if the character _c_ falls into the
tested class, and zero if not.ATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ **Interface** │ **Attribute** │ **Value** │
├──────────────────────────────────────┼───────────────┼─────────┤
│ **isalnum**(), **isalpha**(), **isascii**(), │ Thread safety │ MT-Safe │
│ **isblank**(), **iscntrl**(), **isdigit**(), │ │ │
│ **isgraph**(), **islower**(), **isprint**(), │ │ │
│ **ispunct**(), **isspace**(), **isupper**(), │ │ │
│ **isxdigit**() │ │ │
└──────────────────────────────────────┴───────────────┴─────────┘STANDARDS top
**isalnum**()
**isalpha**()
**iscntrl**()
**isdigit**()
**isgraph**()
**islower**()
**isprint**()
**ispunct**()
**isspace**()
**isupper**()
**isxdigit**()
**isblank**()
C11, POSIX.1-2008.
**isascii**()
**isalnum_l**()
**isalpha_l**()
**isblank_l**()
**iscntrl_l**()
**isdigit_l**()
**isgraph_l**()
**islower_l**()
**isprint_l**()
**ispunct_l**()
**isspace_l**()
**isupper_l**()
**isxdigit_l**()
POSIX.1-2008.
**isascii_l**()
GNU.HISTORY top
**isalnum**()
**isalpha**()
**iscntrl**()
**isdigit**()
**isgraph**()
**islower**()
**isprint**()
**ispunct**()
**isspace**()
**isupper**()
**isxdigit**()
C89, POSIX.1-2001.
**isblank**()
C99, POSIX.1-2001.
**isascii**()
POSIX.1-2001 (XSI).
POSIX.1-2008 marks it as obsolete, noting that it cannot be
used portably in a localized application.
**isalnum_l**()
**isalpha_l**()
**isblank_l**()
**iscntrl_l**()
**isdigit_l**()
**isgraph_l**()
**islower_l**()
**isprint_l**()
**ispunct_l**()
**isspace_l**()
**isupper_l**()
**isxdigit_l**()
glibc 2.3. POSIX.1-2008.
**isascii_l**()
glibc 2.3.CAVEATS top
The standards require that the argument _c_ for these functions is
either **EOF** or a value that is representable in the type _unsigned_
_char_; otherwise, the behavior is undefined. 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 ALSO top
[iswalnum(3)](../man3/iswalnum.3.html), [iswalpha(3)](../man3/iswalpha.3.html), [iswblank(3)](../man3/iswblank.3.html), [iswcntrl(3)](../man3/iswcntrl.3.html), [iswdigit(3)](../man3/iswdigit.3.html),
[iswgraph(3)](../man3/iswgraph.3.html), [iswlower(3)](../man3/iswlower.3.html), [iswprint(3)](../man3/iswprint.3.html), [iswpunct(3)](../man3/iswpunct.3.html), [iswspace(3)](../man3/iswspace.3.html),
[iswupper(3)](../man3/iswupper.3.html), [iswxdigit(3)](../man3/iswxdigit.3.html), [newlocale(3)](../man3/newlocale.3.html), [setlocale(3)](../man3/setlocale.3.html), [toascii(3)](../man3/toascii.3.html),
[tolower(3)](../man3/tolower.3.html), [toupper(3)](../man3/toupper.3.html), [uselocale(3)](../man3/uselocale.3.html), [ascii(7)](../man7/ascii.7.html), [locale(7)](../man7/locale.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-12-11 isalpha(3)
Pages that refer to this page:PR_SET_VMA(2const), getopt(3), iswalnum(3), iswalpha(3), iswblank(3), iswcntrl(3), iswdigit(3), iswgraph(3), iswlower(3), iswprint(3), iswpunct(3), iswspace(3), iswupper(3), iswxdigit(3), localeconv(3), setlocale(3), sscanf(3), strtod(3), strtol(3), strtoul(3), toascii(3), toupper(3), wctype(3), bpf-helpers(7), locale(7), lsof(8)