NationalSecurityAgency/ghidra · error

%s: option `--%s' doesn't allow an argument\n

Error message

%s: option `--%s' doesn't allow an argument\n

What it means

A long option was found (pfound != NULL) but it takes no argument (pfound->has_arg is false). The user attached a value via `--option=value` (nameend is non-empty). The double-dash form is confirmed by argv[optind-1][1] == '-'. opterr is non-zero.

Source

Thrown at GPL/DemanglerGnu/src/demangler_gnu_v2_41/c/getopt.c:710

	}

      if (pfound != NULL)
	{
	  option_index = indfound;
	  optind++;
	  if (*nameend)
	    {
	      /* Don't test has_arg with >, because some C compilers don't
		 allow it to be used on enums.  */
	      if (pfound->has_arg)
		optarg = nameend + 1;
	      else
		{
		  if (opterr)
		    {
		      if (argv[optind - 1][1] == '-')
			/* --option */
			fprintf (stderr,
				 _("%s: option `--%s' doesn't allow an argument\n"),
				 argv[0], pfound->name);
		      else
			/* +option or -option */
			fprintf (stderr,
				 _("%s: option `%c%s' doesn't allow an argument\n"),
				 argv[0], argv[optind - 1][0], pfound->name);

		      nextchar += strlen (nextchar);

		      optopt = pfound->val;
		      return '?';
		    }
		}
	    }
	  else if (pfound->has_arg == 1)
	    {
	      if (optind < argc)

View on GitHub (pinned to d5f144c24d)

Solutions

  1. Remove the `=value` from the flag option
  2. Check `--help` to see which options accept arguments
  3. If you need to set a value, use the correct option that takes one

Example fix

// before
./c++filt --strip-underscore=true
// after
./c++filt --strip-underscore
Defensive patterns

Strategy: validation

Validate before calling

// Verify that a long option accepting an argument is not given one via =value
static int validate_no_arg_attached(int argc, char *const argv[], const struct option *longopts) {
    for (int i = 1; i < argc; i++) {
        if (argv[i][0] != '-' || argv[i][1] != '-') continue;
        char *eq = strchr(argv[i], '=');
        if (!eq) continue;
        size_t len = eq - argv[i] - 2;
        for (const struct option *o = longopts; o->name; o++) {
            if (strncmp(o->name, argv[i] + 2, len) == 0 && strlen(o->name) == len) {
                if (o->has_arg == 0) {
                    fprintf(stderr, "--%s does not accept an argument\n", o->name);
                    return 0;
                }
            }
        }
    }
    return 1;
}

Try / catch

int c;
while ((c = getopt_long(argc, argv, optstring, longopts, NULL)) != -1) {
    if (c == '?') { exit(EXIT_FAILURE); }
}

Prevention

When it happens

Trigger: User passes `--flag=value` where `flag` has has_arg == 0 (no_argument). nameend points to the '=' and is non-empty.

Common situations: Passing `=value` to a boolean/flag option; copy-pasting from a command for a different option that does accept arguments; misunderstanding which options are flags.

Related errors

AI-assisted analysis of NationalSecurityAgency/ghidra@d5f144c24d (2026-08-14). Data as JSON: /api/errors/8ffaad0168f0aff3. Report an issue: GitHub.