Requirements

Implement your own light-weight wc utility, called lwc.c, in C (not C++)

lwc only supports three options -l, -w, and –c; lwc assumes at least one option is provided; lwc only process files (ignore stdin)
lwc supports multiple options; lwc ignore the order of options. The no. lines is always printed first, followed by the no. words and characters. run wc on Ubuntu to make sure that your outputs are identical to it!
If an invalid option or filename is given, lwc prints the same error message wc would print to stderr, and return the same non-zero exit status

Implementation

SYNOPSIS

1 2	#include <unistd.h> int getopt(int argc, char * const argv[],const char *optstring);

另外有些 extern 的變數

optind : The variable optind is the index of the next element to be processed in argv.
opterr : The calling program may prevent the error message by setting opterr to 0.(defualt value is 1)
optopt : The variable optopt is set to the actual option character.