Check valid filename Win32 API

Question

Hi
Is there a Win32 API to check filename validity (for illegal chars and names) or I have to implement it?

Thanks

Answer 1

Finally I implement it:

// This function replaces illegal chars in file name by _
// pstrOut must point to a buffer with MAX_PATH size
void MakeLegalFileName(LPCTSTR pstrIn, LPTSTR pstrOut)
{
    ASSERT(pstrIn);
    ASSERT(pstrOut);

    LPCTSTR pIn = pstrIn;
    LPTSTR pOut = pstrOut;
    LPTSTR pRightTrimPos = pstrOut;
    int nLen = 0;
    *pstrOut = _T('\0');

    while (*pIn != _T('\0') && nLen++ < MAX_PATH)
    {
        if (*pIn > 31)
        {
            switch (*pIn)
            {
            case _T('<'):
            case _T('>'):
            case _T(':'):
            case _T('"'):
            case _T('/'):
            case _T('\\'):
            case _T('|'):
            case _T('?'):
            case _T('*'):
                *pOut = _T('_');
                pOut++;
                break;

            default:
                if (*pIn != _T(' ') || *pstrOut != _T('\0')) // trim left spaces
                {
                    *pOut = *pIn;
                    if (*pOut != _T('.') && *pOut != _T(' ')) // trim right spaces & dots
                        pRightTrimPos = pOut + 1;

                    pOut++;
                }
                break;
            }
        }
        else
        {
            *pOut = _T('_');
            pOut++;
        }
        pIn++;
    }

    *pRightTrimPos = _T('\0');


    static const TCHAR* szSpecialNames[22] = {
         _T("CON"), _T("PRN"), _T("AUX"), _T("NUL"),
         _T("COM1"), _T("COM2"), _T("COM3"), _T("COM4"), _T("COM5"), _T("COM6"), _T("COM7"), _T("COM8"), _T("COM9"),
         _T("LPT1"), _T("LPT2"), _T("LPT3"), _T("LPT4"), _T("LPT5"), _T("LPT6"), _T("LPT7"), _T("LPT8"), _T("LPT9")
    };

    int nOutStrLen = pRightTrimPos - pstrOut;
    if (nOutStrLen == 3)
    {
        for (int i = 0; i < 4; i++)
        {
            if (_tcsicmp(pstrOut, szSpecialNames[i]) == 0)
            {
                pstrOut[2] = _T('_');
                return;
            }
        }
    }
    else if (nOutStrLen == 4)
    {
        for (int i = 4; i < 22; i++)
        {
            if (_tcsicmp(pstrOut, szSpecialNames[i]) == 0)
            {
                pstrOut[3] = _T('_');
                return;
            }
        }
    }
}

Answer 2

There is an API called PathCleanupSpec that will attempt to remove illegal characters,
You don't have to use resultant path, because your goal is to determine if anything was removed
which means you know the path was bad.

You know the path was bad trough return value of PCS_REMOVEDCHAR which means "Removed one or more invalid characters."
Other return values need to be handled as well to get correct result.

https://learn.microsoft.com/en-us/windows/win32/api/shlobj_core/nf-shlobj_core-pathcleanupspec

Answer 3

Unless someone knows of or finds something better, you can use a regular expression. You do not specify a language; the vs-general tag is neither a language nor an API. There are some possible regexes in Regular Expression Library. In C# you can use the Path.GetInvalidPathChars Method in a regex, something like:

Regex containsABadCharacter = new Regex("[" + Regex.Escape(System.IO.Path.InvalidPathChars) + "]");