getsubopt(3C)

getsubopt -- parse suboptions from a string

Synopsis

   #include <stdlib.h>
   
   int getsubopt (char optionp, char const tokens, char valuep);

Description

getsubopt parses suboptions in a flag argument that was initially parsed by getopt. These suboptions are separated by commas and may consist of either a single token or a token-value pair separated by an equal sign. Since commas delimit suboptions in the option string, they are not allowed to be part of the suboption or the value of a suboption. A command that uses this syntax is mount(1M), which allows the user to specify mount parameters with the -o option as follows:

   mount -o rw,hard,bg,wsize=1024 speed:/home /home

In this example there are four suboptions: rw, hard, bg, and wsize, the last of which has an associated value of 1024.

getsubopt takes the address of a pointer to the option string, a vector of possible tokens, and the address of a value string pointer. It returns the index of the token that matched the suboption in the input string or -1 if there was no match. If the option string at optionp contains only one suboption, getsubopt updates optionp to point to the null character at the end of the string; otherwise it isolates the suboption by replacing the comma separator with a null character, and updates optionp to point to the start of the next suboption. If the suboption has an associated value, getsubopt updates valuep to point to the value's first character. Otherwise it sets valuep to NULL.

The token vector is organized as a series of pointers to null terminated strings. The end of the token vector is identified by a null pointer.

When getsubopt returns, if valuep is not NULL, then the suboption processed included a value. The calling program may use this information to determine if the presence or lack of a value for this subobtion is an error.

Additionally, when getsubopt fails to match the suboption with the tokens in the tokens array, the calling program should decide if this is an error, or if the unrecognized option should be passed to another program.

Return values

getsubopt returns -1 when the token it is scanning is not in the token vector. The variable addressed by valuep contains a pointer to the first character of the token that was not recognized rather than a pointer to a value for that token.

The variable addressed by optionp points to the next option to be parsed, or a null character if there are no more options.

Usage

The following code fragment shows how to process options to the mount command using getsubopt.

   #include <stdlib.h>
   char myopts[] = {
   #define READONLY 	0
   			"ro",
   #define READWRITE	1
   			"rw",
   #define WRITESIZE	2
   			"wsize",
   #define READSIZE 	3
   			"rsize",
   			NULL};
   
   main(argc, argv)
   	int  argc;
   	char argv;
   {
   	int sc, c, errflag;
   	char options, value;
   	extern char optarg;
   	extern int optind;
   	.
   	.
   	.
   	while((c = getopt(argc, argv, "abf:o:")) != -1) {
   		switch (c) {
   		case 'a': / process a option /
   			break;
   		case 'b': / process b option /
   			break;
   		case 'f':
   			ofile = optarg;
   			break;
   		case '?':
   			errflag++;
   			break;
   		case 'o':
   			options = optarg;
   			while (options != '\0') {
   				switch(getsubopt(&options,myopts,&value) {
   				case READONLY : / process ro option /
   					break;
   				case READWRITE : / process rw option /
   					break;
   				case WRITESIZE : / process wsize option /
   					if (value == NULL) {
   						error_no_arg();
   						errflag++;
   					} else
   						write_size = atoi(value);
   					break;
   				case READSIZE : / process rsize option /
   					if (value == NULL) {
   						error_no_arg();
   						errflag++;
   					} else
   						read_size = atoi(value);
   					break;
   				default :
   					/ process unknown token /
   					error_bad_token(value);
   					errflag++;
   					break;
   			   	}
   			}
   		  	break;
   		}
   	}
   	if (errflag) {
   		/ print usage instructions etc. /
   	}
   	for (; optind<argc; optind++) {
   		/ process remaining arguments /
   	}
   	.
   	.
   	.
   }

References

getopt(3C)

Notices

During parsing, commas in the option input string are changed to null characters. White space in tokens or token-value pairs must be protected from the shell by quotes.