arduino/Arduino · error · IOException

No valid code files found

Error message

No valid code files found

What it means

listSketchFiles scans the sketch folder for valid source files (.ino/.pde/.c/.cpp/.h etc.) and throws IOException when it finds none. It guarantees a Sketch is never built from an empty or all-invalid directory.

Source

Thrown at arduino-core/src/processing/app/Sketch.java:117

   * part of this sketch. Doesn't modify this SketchData instance, just
   * returns a filtered and sorted list of File objects ready to be
   * passed to the SketchFile constructor.
   *
   * @param showWarnings
   *          When true, any invalid filenames will show a warning.
   */
  private List<SketchFile> listSketchFiles(boolean showWarnings) throws IOException {
    Set<SketchFile> result = new TreeSet<>(CODE_DOCS_COMPARATOR);
    for (File file : FileUtils.listFiles(folder, false, EXTENSIONS)) {
      if (BaseNoGui.isSanitaryName(FileUtils.splitFilename(file).basename)) {
        result.add(new SketchFile(this, file));
      } else if (showWarnings) {
        System.err.println(I18n.format(tr("File name {0} is invalid: ignored"), file.getName()));
      }
    }

    if (result.size() == 0)
      throw new IOException(tr("No valid code files found"));

    return new ArrayList<>(result);
  }

  /**
   * Create the data folder if it does not exist already. As a
   * convenience, it also returns the data folder, since it's likely
   * about to be used.
   */
  public File prepareDataFolder() {
    File dataFolder = getDataFolder();
    if (!dataFolder.exists()) {
      dataFolder.mkdirs();
    }
    return dataFolder;
  }

  public void save() throws IOException {

View on GitHub (pinned to a0df6e0e83)

Solutions

1. Put at least one valid .ino/.pde source file (with a valid file name) in the sketch folder
2. Rename files to valid names (alphanumeric + underscore, starting with a letter)
3. Open the correct folder — the one containing the code, not its parent
4. Create a new sketch via File > New instead of opening the empty folder

Example fix

// before
new Sketch(new File("emptySketch"), main);
// after
File dir = new File("emptySketch");
File[] entries = dir.listFiles((d, n) -> n.endsWith(".ino"));
if (entries == null || entries.length == 0) {
  System.err.println("Not a sketch folder: no .ino files");
  return;
}
new Sketch(dir, main);

File[] sources = dir.listFiles((d, n) -> n.matches("[A-Za-z0-9_]+\\.(ino|pde|c|cpp|h)") );
if (sources == null || sources.length == 0) {
  throw new IllegalArgumentException("No valid sketch sources in " + dir);
}

static boolean isValidSketchFolder(File dir) {
  File[] f = dir.listFiles((d, n) -> n.toLowerCase().endsWith(".ino") || n.toLowerCase().endsWith(".pde"));
  return dir.isDirectory() && f != null && f.length > 0;
}

try {
  sketch.load();
} catch (IOException e) {
  if ("No valid code files found".equals(e.getMessage())) {
    System.err.println(dir + " has no valid sketch files");
  }
}

When it happens

Trigger: Opening/saving a sketch whose folder contains zero files with a valid sketch extension — e.g. an empty folder, or a folder whose only files have invalid names that were skipped (with warnings when showWarnings is set).

Common situations: Pointing the IDE at an empty directory; a sketch moved from Windows where files got stripped; files with illegal characters in names silently ignored.

Understand the failure class

Background: EmptyResultError / "no results found": when an API or scraper succeeds but returns zero rows — this error's family across 9 libraries.

Related errors

• The sketch already contains a file named "{0}"
• no headers files (.h) found in {0}
• 'Missing '' + p + '' from library'

AI-assisted analysis of arduino/Arduino@a0df6e0e83 (2026-09-06). Data as JSON: /api/errors/4430471ba7066011. Report an issue: GitHub.