ANSI 4.3.1 The sets of characters tested for by the isalnum, isalpha, iscntrl, islower, isprint, and isupper functions
The following list describes these functions as they are implemented by the Microsoft C compiler.
| Function | Tests For |
| isalnum | Characters 0 – 9, A–Z, a–z ASCII 48–57, 65–90, 97–122 |
| isalpha | Characters A–Z, a–z ASCII 65–90, 97–122 |
| iscntrl | ASCII 0 –31, 127 |
| islower | Characters a–z ASCII 97–122 |
| isprint | Characters A–Z, a–z, 0 – 9, punctuation, space ASCII 32–126 |
| isupper | Characters A–Z ASCII 65–90 |