Command Line Options- getopt

1、command line options: getoptilude getopt .h tern char *optarg ; extern int optind , opterr , optopt ; int getopt_long (int argc , char * const argv , const char *optsing , const struct option *longopts , int *longindex optarg : if an option takes an argument, the pointer will point at that argument.

2、 optind : is the index of the next element to be process in argv . the system initializes this value to 1 . the caller can , the optind value could be equal to argc or than argc . if optind argc, means there are verbose arguments left cannot be parse by getopt (). opterr, optopt : if getopt () does

3、not recognize an option character, it prints an error message to stderr , stores the character in optopt , and returns '? '. the calling program may prevent the error message by setting opterr . parameters argc : the count of input parameters, which passed to the main() function on program i

4、nvoion. argv : the array of input parameters, which passed to the main() function on program invocation. optstring : a character string containing the val short options, each a single letter. an option that requires an argument is followed by a on. for your program, the string ho:v indicates that th

5、e valid options are -h, -o, and -v, with the second of these options followed by an argument. if a character is followed by a colon, means the option requires an argument. for example: ho:v , means option o requires an argument, used as: "-o arg ". if a character is followed by two colons,

6、 means the option takes an optional argument. for example: ho:v , means option o takes an optional argument, used as: "-oarg ", or "-o ". we should notice that if we use "-o arg " under the circumstances, "arg " will not be parsed as the argument of option &qu

7、ot;o ". longopts : a pointer to the first element of an array of struct option declared in getopt.h as struct option const char *name; int has_arg; int *flag; int val; ; the meanings of the erent fields are: name is the name of the long option. has_arg is: no_argument (or 0) if the option does

8、not take an argument; required_argument (or 1) if the option requires an argument; optional_argument (or 2) if the option takes an optional argument. flag specifies how relts are returned for a long option. if flag is null , then getopt_long() returns val. (for example, the calling program may set v

9、al to the equivalent short option character.) otherwise, getopt_long() returns 0, and flag points to a variable which is set to val if the option is found, but left unchanged if the option is not found. val is the value to return, or to load into the variable pointed to by flag. longindex : if it is

10、 not null , it points to a variable which is set to the index of the long option relative to longopts . return value if an option was successfully found, then getopt() returns the option character. if all command-line options have been parsed, then getopt() returns -1 . if getopt() encounters an opt

11、ion character that was not in optstring, then '?' is returned. if getopt() encounters an option with a missing argument, then the return value depends on the first character in optstring: if it is ':', then ':' is returned; otherwise '?' is returned. after all command

12、-line options have been parsed, the optind value could be equal to argc or less than argc . if optind argc, means there are verbose arguments left which cannot be parse by getopt (). under the circumstances, these verbose arguments can be feached from the changed(by getopt() ) array argv from argvin

13、d to argvargc-1 sample code note: the following code is written under the stardard of c99, use blow command to compile: 280047shni145 code $ gcc -wall -std=gnu99 -g getopt.c -o getopt include getopt.h include stdio.h include stdlib.h /* the name of this program. */ const char* program_name; /* print

14、s usage infoation for this program to stream (typically stdout or stderr), * and exit program with exit_code. does not return. */ void print_usage(file* stream, int exit_code, const char* error_message) if(error_message != null) fprintf(stream, "%s n", error_message); fprintf(stream, "

15、;usage: %s options input .n", program_name); fprintf(stream, " -h -help display this usage information. n" " -f file -output filename write output to file. n" " -o arg -optional print optional argument. n"); exit(exit_code); void print_argument(const int option, co

16、nst char* argument) if(argument != null) printf("%c = %s n", option, argument); void print_verbose_arguments(const int argc, char* const* argv) for(int i=optind; i argc; i+) printf("verbose argument: %sn", argvi); void reset_optind(void) optind = 1; void parse_parameters(const in

17、t argc, char* const* argv, const char* const optstring, const struct option* longopts) int next_option = 0; if(argc = 1) print_usage(stdout, 0, null); ee reset_optind(); while(next_option = getopt_long(argc, argv, optstring, longopts, null), next_option != -1) if(next_option = 'h') print_usa

18、ge(stdout, 0, null); else if(next_option = 'f') print_argument(next_option, optarg); else if(next_option = 'o') print_argument(next_option, optarg); else if(next_option = '?') print_usage(stderr, 1, null); print_verbose_arguments(argc, argv); int main(int argc, char* argv) /*

19、 a string listing valid short options letters. */ const char* const short_options = "hf:o:" /* an array descri valid long options. */ const struct option long_options = .name="help", .has_arg=no_argument, .flag=null, .val='h' , .name="output", .has_arg=required_

20、argument, .flag=null, .val='f' , .name="option", .has_arg=optional_argument, .flag=null, .val='o' , .name=null, .has_arg=no_argument, .flag=null, .val=0 ; /* remember the name of the program, to incorporate in messages. * the name is stored in argv0. */ program_name = argv0

21、; parse_parameters(argc, argv, short_options, long_options); return 0; test 280047shni145 code $ ./getopt -h usage: ./getopt options inputfile . -h -help display this usage information. -f file -output filename write output to file. -o arg -optional print optional argument. 280047shni145 code $ ./getopt -f file f = file 280047shni145 code $ ./getopt -oarg o = arg 280047shni145 code $ ./getopt -o arg verbose argument: arg 280047shni145 code $ ./getopt 11 22 33 44 -f 55 -o