What causes "%s: missing argument for dc-scan-opt " in DrKLO/Telegram?

Supply an integer mode value, e.g. `cjpeg -dc-scan-opt 1 ...`.

%s: missing argument for dc-scan-opt

Error message

%s: missing argument for dc-scan-opt

What it means

The -dc-scan-opt switch requires a following integer argument (the DC scan optimization mode, passed to jpeg_c_set_int_param with JINT_DC_SCAN_OPT_MODE via atoi). cjpeg finds no token after -dc-scan-opt, prints this message, and calls usage() which exits.

Source

Thrown at TMessagesProj/jni/mozjpeg/cjpeg.c:404

        usage();
      icc_filename = argv[argn];

    } else if (keymatch(arg, "maxmemory", 3)) {
      /* Maximum memory in Kb (or Mb with 'm'). */
      long lval;
      char ch = 'x';

      if (++argn >= argc)       /* advance to next argument */
        usage();
      if (sscanf(argv[argn], "%ld%c", &lval, &ch) < 1)
        usage();
      if (ch == 'm' || ch == 'M')
        lval *= 1000L;
      cinfo->mem->max_memory_to_use = lval * 1000L;

    } else if (keymatch(arg, "dc-scan-opt", 3)) {
      if (++argn >= argc) {      /* advance to next argument */
        fprintf(stderr, "%s: missing argument for dc-scan-opt\n", progname);
        usage();
      }
      jpeg_c_set_int_param(cinfo, JINT_DC_SCAN_OPT_MODE, atoi(argv[argn]));

    } else if (keymatch(arg, "optimize", 1) || keymatch(arg, "optimise", 1)) {
      /* Enable entropy parm optimization. */
#ifdef ENTROPY_OPT_SUPPORTED
      cinfo->optimize_coding = TRUE;
#else
      fprintf(stderr, "%s: sorry, entropy optimization was not compiled in\n",
              progname);
      exit(EXIT_FAILURE);
#endif

    } else if (keymatch(arg, "outfile", 4)) {
      /* Set output file name. */
      if (++argn >= argc) {      /* advance to next argument */
        fprintf(stderr, "%s: missing argument for outfile\n", progname);

View on GitHub (pinned to 45ab8f4308)

Solutions

Supply an integer mode value, e.g. `cjpeg -dc-scan-opt 1 ...`.
Ensure the variable holding the mode is non-empty before invoking cjpeg.

Example fix

# before
cjpeg -dc-scan-opt in.ppm > out.jpg

# after
cjpeg -dc-scan-opt 1 in.ppm > out.jpg

Defensive patterns

Strategy: validation

Validate before calling

# Ensure -dc-scan-opt has a non-empty integer argument.
case "$DCSCAN" in ''|*[!0-9-]*) DCSCAN=1 ;; esac
cjpeg -dc-scan-opt "$DCSCAN" in.ppm > out.jpg

Prevention

Always pass an integer after -dc-scan-opt.
Default the mode variable to a sane value.

When it happens

Trigger: Running `cjpeg -dc-scan-opt` with no value following, or as the last token.

Common situations: Truncated command line; a shell variable for the mode that expanded to nothing.

Related errors

AI-assisted analysis of DrKLO/Telegram@45ab8f4308 (2026-08-14). Data as JSON: /api/errors/adaa786f94df20b4. Report an issue: GitHub.