21.5 Null-terminated sequence utilities [c.strings]
namespace std {
  int isalnum(int c);
  int isalpha(int c);
  int isblank(int c);
  int iscntrl(int c);
  int isdigit(int c);
  int isgraph(int c);
  int islower(int c);
  int isprint(int c);
  int ispunct(int c);
  int isspace(int c);
  int isupper(int c);
  int isxdigit(int c);
  int tolower(int c);
  int toupper(int c);
}
The contents and meaning of the header 
are the same as the C standard library header 
.