WideCharToMultiByte

Hvorfor virker nedenstående kode:

void test(){

    TCHAR a[30] = _T("abc");
    char b[30] ="";
    int al, bl, x;
    DWORD y;

    bl = 3;
    al = 3;

    x = WideCharToMultiByte (CP_ACP, WC_DEFAULTCHAR, a, al, b, bl,NULL, NULL);

    y = GetLastError ();

}

y returner  1004 ERROR_INVALID_FLAGS