What causes "%s: unknown demangling style `%s'\n" in NationalSecurityAgency/ghidra?

Use a valid style name (run `c++filt --help` to see the list)

%s: unknown demangling style `%s'\n

Error message

%s: unknown demangling style `%s'\n

What it means

c++filt's -s option accepts a demangling style name. The name is resolved by cplus_demangle_name_to_style(), which returns unknown_demangling if the string doesn't match any known style. The tool prints the error and returns exit code 1.

Source

Thrown at GPL/DemanglerGnu/src/demangler_gnu_v2_41/c/cxxfilt.c:217

	  break;
	case 't':
	  flags |= DMGL_TYPES;
	  break;
	case 'i':
	  flags &= ~ DMGL_VERBOSE;
	  break;
	case 'v':
	  // print_version ("c++filt");  // Changed 10/31/23
	  printf ("c++filt 2.41\n"); // Changed 10/31/23
	  return 0;
	case '_':
	  strip_underscore = 1;
	  break;
	case 's':
	  style = cplus_demangle_name_to_style (optarg);
	  if (style == unknown_demangling)
	    {
	      fprintf (stderr, "%s: unknown demangling style `%s'\n",
		       program_name, optarg);
	      return 1;
	    }
	  cplus_demangle_set_style (style);
	  break;
	}
    }

  if (optind < argc)
    {
      for ( ; optind < argc; optind++)
	{
	  demangle_it (argv[optind]);
	  putchar ('\n');
	}

      return 0;
    }

View on GitHub (pinned to d5f144c24d)

Solutions

Use a valid style name (run `c++filt --help` to see the list)
Common valid styles: gnu-v3, auto, java, gnat, dlang, rust
Fix the typo in the style name

Example fix

// before
./c++filt -s gnu3
// after
./c++filt -s gnu-v3

Defensive patterns

Strategy: validation

Validate before calling

// Validate the style name before passing to -s
#include <string.h>
static const char *valid_styles[] = {
    "auto", "gnu", "lucid", "arm", "hp", "edg",
    "gnu-v3", "java", "gnat", "dlang", "rust", NULL
};
static int is_valid_style(const char *s) {
    for (int i = 0; valid_styles[i]; i++)
        if (strcmp(valid_styles[i], s) == 0) return 1;
    return 0;
}
// Use before calling the tool or calling cplus_demangle_name_to_style
if (!is_valid_style(optarg)) {
    fprintf(stderr, "Unknown style '%s'. Valid: auto, gnu-v3, java, ...\n", optarg);
    exit(1);
}

Type guard

static int is_known_demangle_style(const char *name) {
    return cplus_demangle_name_to_style(name) != unknown_demangling;
}

Try / catch

enum demangling_styles style = cplus_demangle_name_to_style(optarg);
if (style == unknown_demangling) {
    fprintf(stderr, "Unknown style '%s'. Use --help for valid styles.\n", optarg);
    return EXIT_FAILURE;
}
cplus_demangle_set_style(style);

Prevention

Check style names against a known list before applying
Provide a --help listing of valid styles
Use auto style to let the demangler detect the format automatically

When it happens

Trigger: User passes `-s bogus`; cplus_demangle_name_to_style(optarg) returns unknown_demangling. Valid styles include auto, gnu, lucid, arm, hp, edg, gnu-v3, java, gnat, dlang, rust.

Common situations: Typo in the style name (e.g. `gnu3` instead of `gnu-v3`); using a style name from a different version; misunderstanding the supported style list.

Related errors

AI-assisted analysis of NationalSecurityAgency/ghidra@d5f144c24d (2026-08-14). Data as JSON: /api/errors/141886c6f4a0a37b. Report an issue: GitHub.