isprint —
printing character test (space character inclusive)
Standard C Library (libc, -lc)
#include <ctype.h>
int
  
  isprint(int
    c);
The isprint() function tests for any printing character
  including space (' ').
The isprint() function returns zero if the character
  tests false and returns non-zero if the character tests true.
ctype(3),
  isalnum(3),
  isalpha(3),
  isascii(3),
  isblank(3),
  iscntrl(3),
  isdigit(3),
  isgraph(3),
  islower(3),
  ispunct(3),
  isspace(3),
  isupper(3),
  isxdigit(3),
  stdio(3),
  toascii(3),
  tolower(3),
  toupper(3),
  ascii(7)
The isprint() function conforms to ANSI
  X3.159-1989 (“ANSI C89”).
The argument to isprint() must be
  EOF or representable as an unsigned
  char; otherwise, the behavior is undefined. See the
  CAVEATS section of
  ctype(3) for more details.