toascii —
convert a byte to 7-bit ASCII
Standard C Library (libc, -lc)
#include <ctype.h>
int
  
  toascii(int
    c);
The toascii() function returns the argument with all but
  the lower 7 bits cleared.
The toascii() function always returns a valid ASCII
  character. The result is a non-negative integer in the range from 0 to 127,
  inclusive.
ctype(3),
  isalnum(3),
  isalpha(3),
  isascii(3),
  iscntrl(3),
  isdigit(3),
  isgraph(3),
  islower(3),
  isprint(3),
  ispunct(3),
  isspace(3),
  isupper(3),
  isxdigit(3),
  stdio(3),
  tolower(3),
  toupper(3),
  ascii(7)
The toascii() function conforms to
  X/Open Portability Guide Issue 4
  (“XPG4”) and IEEE Std 1003.1-2001
  (“POSIX.1”). The IEEE Std 1003.1-2008
  (“POSIX.1”) revision however marked it as obsolete,
  noting that toascii() cannot be used portably in a
  localized application.