Getopt () function

Before we discuss this function, we first understand two concepts: options and their parameters

Gcc-o program PROGRAM.C

In the above command,-O is the option program is the parameter.

Getopt ();

Header file:

#include <unistd.h>

Function Prototypes:

int getopt (int argc,char * CONST argv[],const char * optstring);

ARGC is the number of arguments, and argv is an array of pointers.

External variables

extern char *optarg; The parameter pointer of the option, pointing to the next parameter to be scanned

extern int Optind,//index as subscript for next pointer to be processed

extern int Opterr,//When opterr=0, getopt does not output error messages to stderr, instead of 0, an error message is printed to Sterr

extern int optopt; Used to store incorrect or unknowable information, which is stored in optopt,getopt returns a question mark (?) when the command-line option character is not included in optstring or if the option lacks the necessary parameters.

　　Optstring the specifications of the parameters

1. Single character, indicating options,
2. A single character followed by a colon (:) indicates that the option must follow a parameter. Parameters are immediately followed by options or separated by a space. The pointer to the parameter is assigned to Optarg.
3 A single character followed by a two colon (::), which indicates that the parameter after the option is optional. If so, the parameters must be immediately followed by an option and cannot be separated by a space. The pointer to the parameter is assigned to Optarg.

e.g.

/*getopt.c*/
1#include <stdio.h>2#include <stdlib.h>3#include <unistd.h>4 intMainintargcChar*argv[])5 {6     intopt;7      while(Opt=getopt (ARGC,ARGV,"ab:c::"))!=-1){8         Switch(opt) {9              Case 'a':Tenprintf"option:%c\n", opt); One                  Break; A              Case 'b': -printf"optarg1:%s\n", optarg); -                  Break; the              Case 'C': -printf"optarg2:%s\n", optarg); -                  Break; -              Case '?': +printf"unknown option:%c\n", optopt); -                  Break; +         } A     } at      for(; optind<argc;optind++) -printf"argument:%s\n", Argv[optind]); -Exit0); -}

Compiling Gcc-o getopt getopt.c

Run for the first time./getopt-a-B "I am OK"-C

Results　

　　　　Option:a

Optarg1:i am OK

OPTARG2: (NULL)

Run the second time./getopt-a-B "I am OK"-C "I am OK"

Results

Option:a

Optarg1:i am OK

Optarg2:i AM OK

　　

Getopt () function