Remarks
These routines test characters for specified conditions.
The is routines produce meaningful results for any integer argument from –1 (EOF) to UCHAR_MAX (0xFF), inclusive. The expected argument type is int.
Warning For the is routines, passing an argument of type char may yield unpredictable results. An SBCS or MBCS single-byte character of type char with a value greater than 0x7F is negative. If a char is passed, the compiler may convert the value to a signed int or a signed long. This value may be sign-extended by the compiler, with unexpected results.
The isw routines produce meaningful results for any integer value from – 1 (WEOF) to 0xFFFF, inclusive. The wint_t data type is defined in WCHAR.H as an unsigned short; it can hold any wide character or the wide-character end-of-file (WEOF) value.
For each of the is routines, the result of the test for the specified condition depends on the LC_CTYPE category setting of the current locale; see setlocale for more information. In the “C” locale, the test conditions for the is routines are as follows:
isalnum
Alphanumeric (A – Z, a – z, or 0 – 9)
isalpha
Alphabetic (A – Z or a – z)
__isascii
ASCII character (0x00 – 0x7F)
iscntrl
Control character (0x00 – 0x1F or 0x7F)
__iscsym
Letter, underscore, or digit
__iscsymf
Letter or underscore
isdigit
Decimal digit (0 – 9)
isgraph
Printable character except space ( )
islower
Lowercase letter (a – z)
isprint
Printable character including space (0x20 – 0x7E)
ispunct
Punctuation character
isspace
White-space character (0x09 – 0x0D or 0x20)
isupper
Uppercase letter (A – Z)
isxdigit
Hexadecimal digit (A – F, a – f, or 0 – 9)
For the isw routines, the result of the test for the specified condition is independent of locale. The test conditions for the isw functions are as follows:
iswalnum
iswalpha or iswdigit
iswalpha
Any wide character that is one of an implementation-defined set for which none of iswcntrl, iswdigit, iswpunct, or iswspace is true. iswalpha returns true only for wide characters for which iswupper or iswlower is true.
iswascii
Wide-character representation of ASCII character (0x0000 – 0x007F).
iswcntrl
Control wide character.
iswctype
Character has property specified by the desc argument. For each valid value of the desc argument of iswctype, there is an equivalent wide-character classification routine, as shown in the following table:
Equivalence of iswctype( c, desc ) to Other isw Testing Routines
| Value of desc Argument | iswctype( c, desc ) Equivalent |
| _ALPHA | iswalpha( c ) |
| _ALPHA | _DIGIT | iswalnum( c ) |
| _CONTROL | iswcntrl( c ) |
| _DIGIT | iswdigit( c ) |
| _ALPHA | _DIGIT | _PUNCT | iswgraph( c ) |
| _LOWER | iswlower( c ) |
| _ALPHA | _BLANK | _DIGIT | _PUNCT | iswprint( c ) |
| _PUNCT | iswpunct( c ) |
| _SPACE | iswspace( c ) |
| _UPPER | iswupper( c ) |
| _HEX | iswxdigit( c ) |
iswdigit
Wide character corresponding to a decimal-digit character.
iswgraph
Printable wide character except space wide character (L' ').
iswlower
Lowercase letter, or one of implementation-defined set of wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspace is true. iswlower returns true only for wide characters that correspond to lowercase letters.
iswprint
Printable wide character, including space wide character (L' ').
iswpunct
Printable wide character that is neither space wide character (L' ') nor wide character for which iswalnum is true.
iswspace
Wide character that corresponds to standard white-space character or is one of implementation-defined set of wide characters for which iswalnum is false. Standard white-space characters are: space (L' '), formfeed (L'\f'), newline (L'\n'), carriage return (L'\r'), horizontal tab (L'\t'), and vertical tab (L'\v').
iswupper
Wide character that is uppercase or is one of an implementation-defined set of wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspace is true. iswupper returns true only for wide characters that correspond to uppercase characters.
iswxdigit
Wide character that corresponds to a hexadecimal-digit character.
Example
/* ISFAM.C: This program tests all characters between 0x0
* and 0x7F, then displays each character with abbreviations
* for the character-type codes that apply.
* Editor's note: the following output is significantly
* shortened with the use of ellipses. This full output
* is too long and repetitive.
*/
#include <stdio.h>
#include <ctype.h>
void main( void )
{
int ch;
for( ch = 0; ch <= 0x7F; ch++ )
{
printf( "%.2x ", ch );
printf( " %c", isprint( ch ) ? ch : '\0' );
printf( "%4s", isalnum( ch ) ? "AN" : "" );
printf( "%3s", isalpha( ch ) ? "A" : "" );
printf( "%3s", __isascii( ch ) ? "AS" : "" );
printf( "%3s", iscntrl( ch ) ? "C" : "" );
printf( "%3s", __iscsym( ch ) ? "CS " : "" );
printf( "%3s", __iscsymf( ch ) ? "CSF" : "" );
printf( "%3s", isdigit( ch ) ? "D" : "" );
printf( "%3s", isgraph( ch ) ? "G" : "" );
printf( "%3s", islower( ch ) ? "L" : "" );
printf( "%3s", ispunct( ch ) ? "PU" : "" );
printf( "%3s", isspace( ch ) ? "S" : "" );
printf( "%3s", isprint( ch ) ? "PR" : "" );
printf( "%3s", isupper( ch ) ? "U" : "" );
printf( "%3s", isxdigit( ch ) ? "X" : "" );
printf( "\n" );
}
}
Output
00
01
02
03
04
05
06
07
08
09
0a
0b
0c
0d
0e
0f
10
11
12
13
14
15
16
17
18
19
1a
1b
1c
1d
1e
1f
20 AS S PR
21 ! AS G PU PR
22 " AS G PU PR
23 # AS G PU PR
24 $ AS G PU PR
25 % AS G PU PR
26 & AS G PU PR
27 ' AS G PU PR
28 ( AS G PU PR
29 ) AS G PU PR
2a * AS G PU PR
2b + AS G PU PR
2c , AS G PU PR
2d - AS G PU PR
2e . AS G PU PR
2f / AS G PU PR
30 0 AN AS CS D G PR X
31 1 AN AS CS D G PR X
32 2 AN AS CS D G PR X
33 3 AN AS CS D G PR X
34 4 AN AS CS D G PR X
35 5 AN AS CS D G PR X
36 6 AN AS CS D G PR X
37 7 AN AS CS D G PR X
38 8 AN AS CS D G PR X
.
.
.
39 9 AN AS CS D G PR X
3a : AS G PU PR
3b ; AS G PU PR
3c < AS G PU PR
3d = AS G PU PR
.
.
.
3e > AS G PU PR
3f ? AS G PU PR
40 @ AS G PU PR
41 A AN A AS CS CSF G PR U X
42 B AN A AS CS CSF G PR U X
43 C AN A AS CS CSF G PR U X
44 D AN A AS CS CSF G PR U X
45 E AN A AS CS CSF G PR U X
46 F AN A AS CS CSF G PR U X
47 G AN A AS CS CSF G PR U
48 H AN A AS CS CSF G PR U
49 I AN A AS CS CSF G PR U
4a J AN A AS CS CSF G PR U
4b K AN A AS CS CSF G PR U
4c L AN A AS CS CSF G PR U
4d M AN A AS CS CSF G PR U
4e N AN A AS CS CSF G PR U
4f O AN A AS CS CSF G PR U
50 P AN A AS CS CSF G PR U
51 Q AN A AS CS CSF G PR U
52 R AN A AS CS CSF G PR U
53 S AN A AS CS CSF G PR U
54 T AN A AS CS CSF G PR U
55 U AN A AS CS CSF G PR U
56 V AN A AS CS CSF G PR U
57 W AN A AS CS CSF G PR U
58 X AN A AS CS CSF G PR U
59 Y AN A AS CS CSF G PR U
5a Z AN A AS CS CSF G PR U
5b [ AS G PU PR
5c \ AS G PU PR
5d ] AS G PU PR
5e ^ AS G PU PR
5f _ AS CS CSF G PU PR
60 ` AS G PU PR
61 a AN A AS CS CSF G L PR X
62 b AN A AS CS CSF G L PR X
63 c AN A AS CS CSF G L PR X
64 d AN A AS CS CSF G L PR X
65 e AN A AS CS CSF G L PR X
66 f AN A AS CS CSF G L PR X
67 g AN A AS CS CSF G L PR
68 h AN A AS CS CSF G L PR
69 i AN A AS CS CSF G L PR
6a j AN A AS CS CSF G L PR
6b k AN A AS CS CSF G L PR
6c l AN A AS CS CSF G L PR
6d m AN A AS CS CSF G L PR
6e n AN A AS CS CSF G L PR
6f o AN A AS CS CSF G L PR
70 p AN A AS CS CSF G L PR
71 q AN A AS CS CSF G L PR
72 r AN A AS CS CSF G L PR
73 s AN A AS CS CSF G L PR
74 t AN A AS CS CSF G L PR
75 u AN A AS CS CSF G L PR
76 v AN A AS CS CSF G L PR
77 w AN A AS CS CSF G L PR
78 x AN A AS CS CSF G L PR
79 y AN A AS CS CSF G L PR
7a z AN A AS CS CSF G L PR
7b { AS G PU PR
7c | AS G PU PR
7d } AS G PU PR
7e ~ AS G PU PR
7f
Character Classification Routines | Locale Routines
See Also setlocale, to Function Overview