I am trying to use getopt_long_only() with custom error messages. The code is shown below. I tried setting opterr=0 and using a colon at the start of the optstring to disable built-in error messages. I added a block of code controlled with boolean optoptWorks = true to try to customize error messages, for example to print a message when a bad option like -z is used. However optopt is always set to 0 and the ? error message that I am using does not make sense. The ':' (colon case) errors (missing argument such as -d) does work OK for custom messages. Turning built-in error messages off and handling in ? seems to result in optopt always being set to 0 so I can't print the offending option (-z is not recognized). I compiled on Debian Linux gcc 4.9.4 and also Cygwin gcc 7.3.0 and both give the same result. It seems like getopt_long_only() may not set optopt properly or am I missing something? Many examples on the web get around this by either using the built-in error messages or just printing usage without telling the user which option is not recognized.
Here is output with optoptWorks=false:
$ ./testoptget -z
testoptget: unknown option -- z
-d # Set the debug level.
-h, --help Print program usage.
-q Run in quiet mode (log messages to syslog but not console).
-v, --version Print program version.
$ ./testoptget -d
testoptget: option requires an argument -- d
-d # Set the debug level.
-h, --help Print program usage.
-q Run in quiet mode (log messages to syslog but not console).
-v, --version Print program version.
and here is output with optoptWorks=true:
$ ./testoptget -z
[ERROR] Unknown option character '\x0'.
-d # Set the debug level.
-h, --help Print program usage.
-q Run in quiet mode (log messages to syslog but not console).
-v, --version Print program version.
$ ./testoptget -d
[ERROR] Option '-d' is missing argument.
-d # Set the debug level.
-h, --help Print program usage.
-q Run in quiet mode (log messages to syslog but not console).
-v, --version Print program version.
The code follows:
/*
Test program for getopt_long_only
*/
#include <ctype.h>
#include <getopt.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
int debug = 0; /* Default to not debugging */
/**
Print the program usage.
*/
void usage(void)
{
/* Print the program name and version */
printf("\n");
printf("-d # Set the debug level.\n");
printf("-h, --help Print program usage.\n");
printf("-q Run in quiet mode (log messages to syslog but not console).\n");
printf("-v, --version Print program version.\n\n");
exit(0);
}
/**
Parse command line parameters and set data for program.
@param argc number of command line parameters
@param argv list of command line parameters
*/
void parseargs(int argc,char **argv)
{ /*
See: https://www.gnu.org/software/libc/manual/html_node/Getopt.html#Getopt
See: http://man7.org/linux/man-pages/man3/getopt.3.html
Because legacy -version and --version need to be supported, use getopts_long_only.
*/
/*
The meaning of the following is:
name - the name of the long option
has_arg - whether the option has an argument like --arg param or --arg=param
flag - the numeric value to return (set to "opt" below), if NULL or zero, return "val"
val - the value to return (set to "opt" below) if "flag" not set, use the one-character equivalent
*/
static struct option long_options[] = {
{ "help", no_argument, 0, 'h' }, /* returns as if -v, index not needed */
{ "version", no_argument, 0, 'v' }, /* returns as if -h, index not needed */
{ 0, 0, 0, 0 } /* last element of array must be zeros */
};
int long_index = 0;
int opt;
int errorCount = 0;
/* In <unistd.h>: external int optind, opterr, optopt */
bool optoptWorks = false; /* Apparently optopt gets set to 0 for unknown argument so let the getopt_long_only print the error */
char optstring[32] = "d:hqv";
if ( optoptWorks ) {
/*
If getopt_long_only works as it is supposed to...
Set opterr to zero so getopt calls won't print an error - check for errors in '?' return value
Also use : as first character of optstring to cause : to be used for error handling
*/
opterr = 0;
/* Do the following because strcat is not safe on overlapping strings */
char optstring2[32];
strcpy(optstring2,optstring);
strcpy(optstring,":");
strcat(optstring,optstring2);
}
while((opt = getopt_long_only(argc, argv, optstring, long_options, &long_index)) != -1) {
switch (opt) { /* Will match single character option or long_options val or flag */
case 'd':
/* -d #, Set the debug level to the argument value */
debug = atoi(optarg);
break;
case 'h':
/*
-h, print the usage and exit
-help
--help
*/
usage();
exit(0);
break;
case 'q':
/* -q, indicate that messages should not be printed to stdout */
break;
case 'v':
/*
-v, print the version via standard function,
-version
--version
*/
break;
case ':':
/*
This is an error indicator indicated by : at the start of get_opt_long 3rd argument.
Handle missing argument, such as -d but no argument.
*/
fprintf(stderr, "[ERROR] Option '-%c' is missing argument.\n", optopt);
++errorCount;
break;
case '?':
/*
Handle unknown parameters as per getopt man page example.
"optopt" should contain the offending argument, but perhaps matches last long argument (zero record).
Note that legacy ? command line parameter is no longer supported.
*/
if (isprint(optopt)) {
/* Printable character so print it in the warning. */
if ( optoptWorks ) {
fprintf(stderr, "[ERROR] Unknown option '-%c'.\n", optopt);
}
++errorCount;
}
else {
/* Nonprintable character so show escape sequence. */
if ( optoptWorks ) {
fprintf(stderr, "[ERROR] Unknown option character '\\x%x'.\n", optopt);
}
++errorCount;
}
break;
} /* end switch */
} /* end while */
if ( errorCount > 0 ) {
usage();
exit(1);
}
}
/**
Main program.
@param argc number of command line parameters
@param argv list of command line parameters
@param arge list of environment variables
*/
int main(int argc,char **argv,char **arge)
{
/* Parse command arguments */
parseargs(argc,argv);
/* Normal program termination */
return(0);
}
optopt is indeed set to zero when unknown long option is found, see here. However seems to me you can use optind - 1 as the index in argv to print the offending option, as optind is incremented here right before getopt returns '?'.
As far as I understood, your goal is to just specify custom error messages.
Also from man getopt_long:
If the first character (following any optional '+' or '-' described above) of optstring is a colon (':'), then getopt() likewise does not print an error message. In addition, it returns ':' instead of '?' to indicate a missing option argument. This allows the caller to distinguish the two different types of errors.
The documentation you referenced is about getopt not about getopt_long_only. The man getopt_long_only indeed says that getopt_long() function works like getopt() but the optopt is set to the "option character". In case of long options there is no "option character" but an "option string" (as I would call it) - seems to me logical to set optopt as zero.
So depending on the initial character in optstring, the : or ? is returned, as implemented here and here and here.
The following program is your's with comments removed, shorted usage function, substituted exit for return and added printing offending option with just printf("%s", argv[opting - 1]);:
#include <ctype.h>
#include <getopt.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
int debug = 0;
void usage(void) { printf("-- insert usage here --\n"); }
void parseargs(int argc,char **argv)
{
static struct option long_options[] = {
{ "help", no_argument, 0, 'h' },
{ "version", no_argument, 0, 'v' },
{ 0, 0, 0, 0 }
};
int long_index = 0;
int opt;
int errorCount = 0;
optind = 1;
while((opt = getopt_long_only(argc, argv, ":d:hqv", long_options, &long_index)) != -1) {
switch (opt) {
case 'd':
debug = atoi(optarg);
break;
case 'h':
usage();
return;
break;
case 'q':
break;
case 'v':
break;
case ':':
fprintf(stderr, "[ERROR] Option '-%c' is missing argument.\n", optopt);
++errorCount;
break;
case '?':
if (optopt == 0) {
fprintf(stderr, "[ERROR] Unknown option '%s'.\n", argv[optind - 1]);
} else {
fprintf(stderr, "[ERROR] Error parsing option '-%c'\n", optopt);
}
++errorCount;
break;
}
}
if ( errorCount > 0 ) {
usage();
return;
}
}
int main(int argc, char **argv)
{
#define SIZE(x) (sizeof(x)/sizeof(*x))
struct {
int argc;
char **argv;
} tests[] = {
{ 2, (char*[]){ argv[0], (char[]){"-z"}, NULL, } },
{ 2, (char*[]){ argv[0], (char[]){"-d"}, NULL, } },
};
for (int i = 0; i < SIZE(tests); ++i) {
printf("\n## test tests[i].argv[1] = %s\n", tests[i].argv[1]);
parseargs(tests[i].argc, tests[i].argv);
}
return 0;
}
Outputs:
## test tests[i].argv[1] = -z
[ERROR] Unknown option '-z'.
-- insert usage here --
## test tests[i].argv[1] = -d
[ERROR] Option '-d' is missing argument.
-- insert usage here --
If optstring is set to "d:hqv" without the leading :, then it falls into the ? case, ie. then the program returns:
## test tests[i].argv[1] = -z
./a.out: unrecognized option '-z'
[ERROR] Unknown option '-z'.
-- insert usage here --
## test tests[i].argv[1] = -d
./a.out: option requires an argument -- 'd'
[ERROR] Error parsing option '-d'
-- insert usage here --