Check if character is alphanumeric
Checks whether c is either a decimal digit or an uppercase or lowercase letter.
The result is true if either isalpha or isdigit would also return true.
Notice that what is considered a letter may depend on the locale being used; In the default "C" locale, what constitutes a letter is what returns true by either isupper or islower.
For a detailed chart on what the different ctype functions return for each character of the standard ANSII character set, see the reference for the <cctype> header.
In C++, a locale-specific template version of this function (isalnum) exists in header <locale>.
- Character to be checked, casted as an int, or EOF.
A value different from zero (i.e., true) if indeed c is either a digit or a letter. Zero (i.e., false) otherwise.
/* isalnum example */
int main ()
while (isalnum(str[i])) i++;
printf ("The first %d characters are alphanumeric.\n",i);
The first 4 characters are alphanumeric.
- Check if character is alphabetic (function)
- Check if character is decimal digit (function)