isdigit

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

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");
}

0123456789

References

• C17 standard (ISO/IEC 9899:2018):
• 7.4.1.5 The isdigit function (p: 146)
• 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