ISUPPER (man3p)
isupper, isupper_l — test for an uppercase letter
isupper, isupper_l — test for an uppercase letter
statvfs — get file system information
sigaction — examine and change a signal action
gethostid — get an identifier for the current host
getopt, optarg, opterr, optind, optopt — command option parsing
wcpcpy, wcscpy — copy a wide-character string, returning a pointer to its end
strtoimax, strtoumax — convert string to integer type
cimag, cimagf, cimagl — complex imaginary functions
perror — write error messages to standard error
twalk — traverse a binary search tree