#include <ctype.h> int isprint(int c);
C/C++ function that returns true if c is classified as a printable character.
In a locale-specific class, no character for the class cntrl can be specified as class print character. Characters specified for the classes upper, lower, alpha, digit, xdigit, punct and the space character are automatically included in the class print.
In the C locale, all characters in class graph are included in the class print; no characters in class cntrl are included.
For the moment this is copied from man pages. I'll re-word in language for mortals just as soon as I have time.