The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.
A newer edition of this document exists here


getsubopt - parse suboption arguments from a string


[XSI] [Option Start] #include <stdlib.h>

int getsubopt(char **
optionp, char * const *keylistp, char **valuep); [Option End]


The getsubopt() function shall parse suboption arguments in a flag argument. Such options often result from the use of getopt().

The getsubopt() argument optionp is a pointer to a pointer to the option argument string. The suboption arguments shall be separated by commas and each may consist of either a single token, or a token-value pair separated by an equal sign.

The keylistp argument shall be a pointer to a vector of strings. The end of the vector is identified by a null pointer. Each entry in the vector is one of the possible tokens that might be found in *optionp. Since commas delimit suboption arguments in optionp, they should not appear in any of the strings pointed to by keylistp. Similarly, because an equal sign separates a token from its value, the application should not include an equal sign in any of the strings pointed to by keylistp.

The valuep argument is the address of a value string pointer.

If a comma appears in optionp, it shall be interpreted as a suboption separator. After commas have been processed, if there are one or more equal signs in a suboption string, the first equal sign in any suboption string shall be interpreted as a separator between a token and a value. Subsequent equal signs in a suboption string shall be interpreted as part of the value.

If the string at *optionp contains only one suboption argument (equivalently, no commas), getsubopt() shall update *optionp to point to the null character at the end of the string. Otherwise, it shall isolate the suboption argument by replacing the comma separator with a null character, and shall update *optionp to point to the start of the next suboption argument. If the suboption argument has an associated value (equivalently, contains an equal sign), getsubopt() shall update *valuep to point to the value's first character. Otherwise, it shall set *valuep to a null pointer. The calling application may use this information to determine whether the presence or absence of a value for the suboption is an error.

Additionally, when getsubopt() fails to match the suboption argument with a token in the keylistp array, the calling application should decide if this is an error, or if the unrecognized option should be processed in another way.


The getsubopt() function shall return the index of the matched token string, or -1 if no token strings were matched.


No errors are defined.

The following sections are informative.


#include <stdio.h>
#include <stdlib.h>

int do_all; const char *type; int read_size; int write_size; int read_only;
const char *mount_opts[] = { [RO_OPTION] = "ro", [RW_OPTION] = "rw", [READ_SIZE_OPTION] = "rsize", [WRITE_SIZE_OPTION] = "wsize", NULL };
int main(int argc, char *argv[]) { char *subopts, *value; int opt;
while ((opt = getopt(argc, argv, "at:o:")) != -1) switch(opt) { case 'a': do_all = 1; break; case 't': type = optarg; break; case 'o': subopts = optarg; while (*subopts != '\0') switch(getsubopt(&subopts, mount_opts, &value)) { case RO_OPTION: read_only = 1; break; case RW_OPTION: read_only = 0; break; case READ_SIZE_OPTION: if (value == NULL) abort(); read_size = atoi(value); break; case WRITE_SIZE_OPTION: if (value == NULL) abort(); write_size = atoi(value); break; default: /* Unknown suboption. */ printf("Unknown suboption `%s'\n", value); break; } break; default: abort(); }
/* Do the real work. */
return 0; }
Parsing Suboptions

The following example uses the getsubopt() function to parse a value argument in the optarg external variable returned by a call to getopt().

#include <stdlib.h>
char *tokens[] = {"HOME", "PATH", "LOGNAME", (char *) NULL };
char *value;
int opt, index;

while ((opt = getopt(argc, argv, "e:")) != -1) { switch(opt) { case 'e' : while ((index = getsubopt(&optarg, tokens, &value)) != -1) { switch(index) { ... } break; ... } } ...








getopt(), the Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h>


First released in Issue 4, Version 2.

Issue 5

Moved from X/OPEN UNIX extension to BASE.

Issue 6

IEEE Std 1003.1-2001/Cor 1-2002, item XSH/TC1/D6/26 is applied, correcting an editorial error in the SYNOPSIS.

End of informative text.

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