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isdigit

Defined in header <ctype.h>
int isdigit( int ch );

Checks if the given character is a numeric character (0123456789).

The behavior is undefined if the value of ch is not representable as unsigned char and is not equal to EOF.

Parameters

ch - character to classify

Return value

Non-zero value if the character is a numeric character, zero otherwise.

Notes

isdigit and isxdigit are the only standard narrow character classification functions that are not affected by the currently installed C locale, although some implementations (e.g. Microsoft in 1252 codepage) may classify additional single-byte characters as digits.

Example

#include <stdio.h>
#include <ctype.h>
#include <limits.h>
 
int main(void)
{
    for (int ndx=0; ndx<=UCHAR_MAX; ndx++)
        if (isdigit(ndx)) printf("%c", ndx);
    printf("\n");
}

Output:

0123456789

References

  • C11 standard (ISO/IEC 9899:2011):
    • 7.4.1.5 The isdigit function (p: 201)
  • C99 standard (ISO/IEC 9899:1999):
    • 7.4.1.5 The isdigit function (p: 182)
  • C89/C90 standard (ISO/IEC 9899:1990):
    • 4.3.1.4 The isdigit function

See also

(C95)
checks if a wide character is a digit
(function)
C++ documentation for isdigit
ASCII values
(hex)
characters

iscntrl
iswcntrl.

isprint
iswprint.

isspace
iswspace.

isblank
iswblank.

isgraph
iswgraph.

ispunct
iswpunct.

isalnum
iswalnum.

isalpha
iswalpha.

isupper
iswupper.

islower
iswlower.

isdigit
iswdigit.

isxdigit
iswxdigit.

0 - 8 0x00-0x08 control codes (NUL, etc.) ≠0 0 0 0 0 0 0 0 0 0 0 0
9 0x09 tab (\t) ≠0 0 ≠0 ≠0 0 0 0 0 0 0 0 0
10 - 13 0x0A-0x0D whitespaces (\n,\v,\f,\r) ≠0 0 ≠0 0 0 0 0 0 0 0 0 0
14 - 31 0x0E-0x1F control codes ≠0 0 0 0 0 0 0 0 0 0 0 0
32 0x20 space 0 ≠0 ≠0 ≠0 0 0 0 0 0 0 0 0
33 - 47 0x21-0x2F !"#$%&'()*+,-./ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
48 - 57 0x30-0x39 0123456789 0 ≠0 0 0 ≠0 0 ≠0 0 0 0 ≠0 ≠0
58 - 64 0x3a-0x40 :;<=>[email protected] 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
65 - 70 0x41-0x46 ABCDEF 0 ≠0 0 0 ≠0 0 ≠0 ≠0 ≠0 0 0 ≠0
71 - 90 0x47-0x5A GHIJKLMNOPQRSTUVWXYZ 0 ≠0 0 0 ≠0 0 ≠0 ≠0 ≠0 0 0 0
91 - 96 0x5B-0x60 [\]^_` 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
97 -102 0x61-0x66 abcdef 0 ≠0 0 0 ≠0 0 ≠0 ≠0 0 ≠0 0 ≠0
103-122 0x67-0x7A ghijklmnopqrstuvwxyz 0 ≠0 0 0 ≠0 0 ≠0 ≠0 0 ≠0 0 0
123-126 0x7B-0x7E {|}~ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
127 0x7F backspace character (DEL) ≠0 0 0 0 0 0 0 0 0 0 0 0

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