Check whether a string is a valid filename with Qt

Question

Is there a way with Qt 4.6 to check if a given QString is a valid filename (or directory name) on the current operating system ? I want to check for th

Answer 1

Based on User7116's answer here:

How do I check if a given string is a legal / valid file name under Windows?

I quit being lazy - looking for elegant solutions, and just coded it. I got:

bool isLegalFilePath(QString path)
{
    // Anything following the raw filename prefix should be legal.
    if (path.left(4)=="\\\\?\\")
        return true;

    // Windows filenames are not case sensitive.
    path = path.toUpper();

    // Trim the drive letter off
    if (path[1]==':' && (path[0]>='A' && path[0]<='Z'))
        path = path.right(path.length()-2);

    QString illegal="<>:\"|?*";

    foreach (const QChar& c, path)
    {
        // Check for control characters
         if (c.toLatin1() > 0 && c.toLatin1() < 32)
            return false;

        // Check for illegal characters
        if (illegal.contains(c))
            return false;
    }

    // Check for device names in filenames
    static QStringList devices;

    if (!devices.count())
        devices << "CON" << "PRN" << "AUX" << "NUL" << "COM0" << "COM1" << "COM2"
                << "COM3" << "COM4" << "COM5" << "COM6" << "COM7" << "COM8" << "COM9" << "LPT0"
                << "LPT1" << "LPT2" << "LPT3" << "LPT4" << "LPT5" << "LPT6" << "LPT7" << "LPT8"
                << "LPT9";

    const QFileInfo fi(path);
    const QString basename = fi.baseName();

    foreach (const QString& s, devices)
        if (basename == s)
            return false;

    // Check for trailing periods or spaces
    if (path.right(1)=="." || path.right(1)==" ")
        return false;

    // Check for pathnames that are too long (disregarding raw pathnames)
    if (path.length()>260)
        return false;

    // Exclude raw device names
    if (path.left(4)=="\\\\.\\")
        return false;

    // Since we are checking for a filename, it mustn't be a directory
    if (path.right(1)=="\\")
        return false;

    return true;
}

Features:

• Probably faster than using regexes
• Checks for illegal characters and excludes device names (note that '\' is not illegal, since it can be in path names)
• Allows drive letters
• Allows full path names
• Allows network path names
• Allows anything after \\?\ (raw file names)
• Disallows anything starting with \\.\ (raw device names)
• Disallows names ending in "\" (i.e. directory names)
• Disallows names longer than 260 characters not starting with \\?\
• Disallows trailing spaces and periods

Note that it does not check the length of filenames starting with \\?\, since that is not a hard and fast rule. Also note, as pointed out here, names containing multiple backslashes and forward slashes are NOT rejected by the win32 API.