1 JMH Associates © 2004, All rights reserved Chapters 2-3 Input/Output With File and Directory Processing

2 JMH Associates © 2004, All rights reserved OBJECTIVES (1 of 2) Upon completion of this Chapter you will be able to:  Describe the Windows file systems  Perform sequential file processing  Perform console I/O and direct access file I/O  Report and analyze system call errors  Describe and use Unicode characters and strings and write generic applications (both Unicode and ASCII characters)  Use Windows mandatory file locking to protect files from concurrent modification by several processes  Perform file and directory management

3 JMH Associates © 2004, All rights reserved OBJECTIVES (2 of 2) You will also be prepared for later Chapters  Memory-mapped files  Process management  Interprocess communication  Threads  Synchronization  Asynchronous I/O

4 JMH Associates © 2004, All rights reserved AGENDAAGENDA Part IFile Systems and Sequential I/O Part IIUnicode and Generic Characters Part IIIConsole I/O Part IVLab 2–A Part VDirect File Access Part VIFile Locking Part VIIFile and Directory Management Lab 3–B

5 JMH Associates © 2004, All rights reserved Part I File Systems and Sequential I/O

6 JMH Associates © 2004, All rights reserved BASIC I/O Basic Windows API file processing functions: CreateFile ReadFile WriteFile CloseHandle We used these, in a very simple program, in Chapter 1

7 JMH Associates © 2004, All rights reserved THE FILE SYSTEMS Windows File Systems  (Virtual) File Allocation Table File System (FAT, VFAT)  The only disk file system for floppies and Windows 9x  NTFS File System (NTFS)  Very large (“huge”) files, secure, robust  Supported on Windows NT (all versions)  CD-ROM File System (CDFS)  Custom file systems  Developed by software vendors

8 JMH Associates © 2004, All rights reserved Windows FILE NAMING (1 of 2) Hierarchical Full pathname can start with a drive name  A:, C:, …  Or with a “share” name  \\servername\sharename Pathname separator is a backslash — \  You can also use / in C

9 JMH Associates © 2004, All rights reserved Windows FILE NAMING (2 of 2) Directory and file names cannot use ASCII 1–31  Or any of : " |  But you can have blanks in file names Case insensitive but case retaining File, directory names up to 255 characters long  250 in Windows 9x A period. separates a file’s name from its extension  The period is in the name; there can be more than one. and.. indicate the current directory and its parent

10 JMH Associates © 2004, All rights reserved CREATING AND OPENING FILES HANDLE CreateFile (LPCTSTR lpName, DWORD dwAccess, DWORD dwShareMode, LPSECURITY_ATTRIBUTES lpsa, DWORD dwCreate, DWORD dwAttrsAndFlags, HANDLE hTemplateFile) Return: A HANDLE to an open file object  INVALID_HANDLE_VALUE in case of failure LPCTSTR will be described in Part II

11 JMH Associates © 2004, All rights reserved CREATING AND OPENING FILES (2 OF 6) Parameters lpName  Pointer to the string naming the file  Length normally limited to 260  \\?\ is an escape prefix allowing long NT path names dwAccess  Access using GENERIC_READ or GENERIC_WRITE  Note: Flags can be combined with |

12 JMH Associates © 2004, All rights reserved CREATING AND OPENING (3 OF 6) dwShareMode  0 — Cannot be shared; not even this process can open another handle  FILE_SHARE_READ — Other processes can read concurrently  FILE_SHARE_WRITE — Other processes can write concurrently lpsa points to a SECURITY_ATTRIBUTES structure  NULL for now

13 JMH Associates © 2004, All rights reserved CREATING AND OPENING (4 OF 6) dwCreate — Create a file, overwrite one, etc.  CREATE_NEW — Fails if the file exists  CREATE_ALWAYS — An existing file will be overwritten  OPEN_EXISTING — Fail if the file does not exist  OPEN_ALWAYS — Open the file or create it if it doesn’t exist  TRUNCATE_EXISTING — File length will be set to zero Note: There is no “open to append” mode  You will need to position to the end of file

14 JMH Associates © 2004, All rights reserved CREATING AND OPENING (5 OF 6) dwAttrsAndFlags — 16 flags and attributes including:  FILE_ATTRIBUTE_NORMAL — No other attributes are set  FILE_ATTRIBUTE_READONLY — Cannot write or delete  FILE_FLAG_OVERLAPPED  FILE_FLAG_SEQUENTIAL_SCAN and FILE_FLAG_RANDOM_ACCESS provide performance hints Attributes are properties of the files themselves Flags are associated with a specific HANDLE  Different HANDLE s to the same file can have different flags  Example: One HANDLE is “overlapped,” another not  Or, one has FILE_FLAG_SEQUENTIAL_SCAN and another FILE_FLAG_RANDOM_ACCESS

15 JMH Associates © 2004, All rights reserved CREATING AND OPENING (6 OF 6) File processing flags include:  FILE_FLAG_WRITE_THROUGH  FILE_FLAG_NO_BUFFERING  FILE_FLAG_DELETE_ON_CLOSE hTemplateFile — Handle of an open GENERIC_READ file  Use the same attributes for the new file

16 JMH Associates © 2004, All rights reserved READING FILES (1 OF 2) BOOL ReadFile (HANDLE hFile, LPVOID lpBuffer, DWORD nNumberOfBytesToRead, LPDWORD lpNumberOfBytesRead, LPOVERLAPPED lpOverlapped) Return: TRUE if the read succeeds  Even if no bytes were read due to an attempt to read past the end of file  FALSE indicates an invalid handle, a handle without GENERIC_READ access, etc.

17 JMH Associates © 2004, All rights reserved READING FILES (2 OF 2) Parameters hFile — File handle with GENERIC_READ access lpBuffer — Me m ory buffer to receive the input data nNumberOfBytesToRead  Number of bytes you expect to read * lpNumberOfBytesRead  Actual number of bytes transferred  Zero indicates end of file lpOverlapped  Points to OVERLAPPED structure ( NULL for now)

18 JMH Associates © 2004, All rights reserved WRITING FILES BOOL WriteFile ( HANDLE hFile, CONST VOID *lpBuffer, DWORD nNumberOfBytesToWrite, LPDWORD lpNumberOfBytesWritten, LPOVERLAPPED lpOverlapped) Return: TRUE if the function succeeds; FALSE otherwise

19 JMH Associates © 2004, All rights reserved CLOSING FILES BOOL CloseHandle (HANDLE hObject) Return: TRUE if the function succeeds; FALSE otherwise This function is general purpose and will be used to close handles to many different object types

20 JMH Associates © 2004, All rights reserved COPYING FILES BOOL CopyFile (LPCTSTR lpExistingFile, LPCTSTR lpNewFile, BOOL fFailIfExists) If a file with the new name already exists, it will be replaced only if fFailIfExists is FALSE This is a “convenience function” and also provides performance

21 JMH Associates © 2004, All rights reserved Part II Unicode and Generic Characters

22 JMH Associates © 2004, All rights reserved UNICODE & GENERIC CHARACTERS Windows NT supports 16-bit characters  WCHAR or wchar_t  To assure maximum flexibility and source portability, define all characters and strings using “generic” type TCHAR  Calculate lengths using sizeof(TCHAR)  Include #define UNICODE (to get WCHAR ) in all source modules (or #undef UNICODE to get CHAR )  Be consistent  Define UNICODE before #include  Also define _ UNICODE consistently for the generic C library

23 JMH Associates © 2004, All rights reserved GENERIC CHARACTERS (2 of 3)  Use the “generic” C library for all string functions  _tprintf in place of printf  _stprintf in place of sprintf  _tcslen in place of strlen  _itot in place of itoa  And MANY more  See the on line help and the lab programs  Generic versions of some functions are not provided  e.g. memchr - Replacements are in the lab solutions

24 JMH Associates © 2004, All rights reserved GENERIC CHARACTERS (3 of 3) Constant strings in one of three forms (first 2 are ANSI C)  The last is a macro "This string uses 8-bit characters" L"This string uses 16-bit characters" _T ("This string uses generic characters")  Expands to “T…” if UNICODE is not defined; L”T…” if it is TEXT macro is the same as _T LPTSTR expands to either char * or wchar_t *

25 JMH Associates © 2004, All rights reserved THE GENERIC C LIBRARY Define _UNICODE consistently with UNICODE  This makes available a wide class of string processing and I/O functions _fgettc, _itot, _ttoi, _totupper, _totlower  And many more — nearly the complete library  Also, locale-specific functions (seven in all): lstrlen, lstrcmp, lstrcpy, lstrcat, …  Be sure to #include after Note: Any _ keyword or function is specific to Microsoft Visual C++ and the Microsoft compiler

26 JMH Associates © 2004, All rights reserved GENERIC CHARACTERS AND THE MAIN PROGRAM Windows main is for ASCII; wmain is for Unicode In place of int main (argc, char * argv[])  or int main (argc, w_char * argv[]) Use #include /* this is after */... int _tmain (int argc, LPTSTR argv[]) The _tmain macro then expands to main or wmain  Depending on definition of _UNICODE This assures correct operation in all circumstances and combinations

27 JMH Associates © 2004, All rights reserved Part III Standard Devices and Console I/O

28 JMH Associates © 2004, All rights reserved STANDARD DEVICES AND CONSOLE I/O (1 of 7) HANDLE GetStdHandle (DWORD dwDevice) Return: A valid handle or INVALID_HANDLE_VALUE for failure BOOL SetStdHandle (DWORD IDStdHandle, HANDLE hHandle) Return: TRUE or FALSE indicating success or failure

29 JMH Associates © 2004, All rights reserved STANDARD DEVICES AND CONSOLE I/O (2 of 7) dwDevice and IDStdHandle  Must have one of these values:  STD_INPUT_HANDLE  STD_OUTPUT_HANDLE  STD_ERROR_HANDLE

30 JMH Associates © 2004, All rights reserved STANDARD DEVICES AND CONSOLE I/O (3 of 7) hHandle  Specifies an open file that is to be the standard device Two reserved pathnames for console input (the keyboard): " CONIN$ " and output (the display): " CONOUT "

31 JMH Associates © 2004, All rights reserved STANDARD DEVICES AND CONSOLE I/O (4 of 7) BOOL SetConsoleMode (HANDLE hConsole, DWORD fdevMode) Return: TRUE if and only if the function succeeds hConsole  Must have GENERIC_WRITE access

32 JMH Associates © 2004, All rights reserved STANDARD DEVICES AND CONSOLE I/O (5 of 7) fDevMode — How characters are processed  ENABLE_WINDOW_INPUT  ENABLE_LINE_INPUT  ENABLE_ECHO_INPUT  ENABLE_PROCESSED_INPUT  ENABLE_PROCESSED_OUTPUT  ENABLE_WRAP_AT_EOL_OUTPUT

33 JMH Associates © 2004, All rights reserved STANDARD DEVICES AND CONSOLE I/O (6 of 7) BOOL ReadConsole (HANDLE hConsoleInput, LPVOID lpvBuffer, DWORD cchToRead, LPDWORD lpcchRead, LPVOID lpvReserved) Return: TRUE if and only if the read succeeds

34 JMH Associates © 2004, All rights reserved STANDARD DEVICES AND CONSOLE I/O (7 of 7) BOOL WriteConsole  Same as ReadConsole BOOL FreeConsole (VOID) BOOL AllocConsole (VOID)

35 JMH Associates © 2004, All rights reserved EXAMPLE: PrintStrings (1 of 3) #include "envirmnt.h" /* UNICODE is defined here */ #include BOOL PrintStrings (HANDLE hOut,...) /* Write the messages to the output handle (hOut) Use WriteConsole (to handle Unicode & console processing) first, as the output will normally be the console. If that fails, use WriteFile. hOut: Handle for output file.... : Variable argument list containing TCHAR strings. The list must be terminated with NULL. */

36 JMH Associates © 2004, All rights reserved PrintStrings (2 of 3) { DWORD MsgLen, Count; BOOL Success = TRUE; LPCTSTR pMsg; va_list pMsgList;/* Current message string */ va_start (pMsgList, hOut); /* Start processing msgs */ while (((pMsg = va_arg (pMsgList, LPCTSTR)) != NULL) && Success) { MsgLen = _tcslen (pMsg); (CONTINUED)

37 JMH Associates © 2004, All rights reserved PrintStrings (3 of 3) /* WriteConsole fails if the handle is associated with a file rather than with a console */ if (!WriteConsole (hOut, pMsg, MsgLen, &Count, NULL) && !WriteFile (hOut, pMsg, MsgLen * sizeof (TCHAR), &Count, NULL)) return FALSE; } /* End of while loop - process next message */ va_end (pMsgList); return TRUE; }

38 JMH Associates © 2004, All rights reserved EXAMPLE: ReportError (1 of 4) OBJECTIVE:  Turn system call errors into meaningful text strings  And print the text  Terminate the program if the error is fatal Similar to perror(), but it works in the multithreaded Windows environment.

39 JMH Associates © 2004, All rights reserved EXAMPLE: ReportError (2 of 4) #include "envirmnt.h" #include #include "support.h" VOID ReportError (LPCTSTR UserMessage, DWORD ExitCode, BOOL PrintErrorMsg) /* General-purpose function to report system errors. Obtain the error number and turn it into the system error message. Display this information and the user specified message to the standard error device. UserMessage: Message to be displayed to standard error device.*/

40 JMH Associates © 2004, All rights reserved ReportError (3 of 4) ExitCode: 0 - Return > 0 - ExitProcess with this code PrintErrorMessage: Display the last system error message if this flag is set. */ { DWORD eMsgLen, ErrNum = GetLastError (); LPVOID lpvSysMsg; HANDLE hStdErr = GetStdHandle (STD_ERROR_HANDLE); PrintMsg (hStdErr, UserMessage); if (PrintErrorMsg) {

41 JMH Associates © 2004, All rights reserved ReportError (4 of 4) eMsgLen = FormatMessage ( FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM, NULL, ErrNum, MAKELANGID (LANG_DFLT, SUBLANG_DFLT), &lpvSysMsg, 0, NULL); PrintStrings (hStdErr, TEXT ("\n"), lpvSysMsg, TEXT ("\n"), NULL); HeapFree (GetProcessHeap (), 0, lpvSysMsg); } if (ExitCode > 0) ExitProcess (ExitCode); else return; }

42 JMH Associates © 2004, All rights reserved LAB 2–A (Option 1) Modify the copy program in Chapter 1 to create the program cpCF which will:  Take the input and output files from the command line  Use the generic macro _tmain  Report all system errors using ReportError ()  Use the CopyFile function  Prompt the user to see if an existing file should be overwritten.

43 JMH Associates © 2004, All rights reserved LAB 2–A (Option 2) Create a program, atou, which behaves just like cp except that the input file is assumed to be in ASCII and the output file will be the Unicode equivalent (and twice as long as the original). Include the asc2un.c source file in your project. We will build several variations of this program during the course to illustrate different file processing techniques.

44 JMH Associates © 2004, All rights reserved LAB 2–A (Option 3) Create a program, cat, that takes multiple file names from the command line and copies them, in order, to standard output. If there are no file names on the command line, use standard input. This program will be required with several future labs. Addtional Note: You will find it convenient to put your working programs (.EXE files) in a common directory, such as RUN (Provided with the solutions).

45 JMH Associates © 2004, All rights reserved Part V Direct File Access

46 JMH Associates © 2004, All rights reserved FILE POINTERS (1 of 4) DWORD SetFilePointer (HANDLE hFile, LONG lDistanceToMove, PLONG lpDistanceToMoveHigh, DWORD dwMoveMethod) Return: The low-order DWORD (unsigned) of the new file pointer. The high-order portion of the new file pointer goes to the DWORD indicated by lpDistanceToMoveHigh (if non- NULL ). In case of error, the return value is OxFFFFFFFF. Note: The file pointer is associated with the HANDLE, not the file. The pointer advances with each read and write.

47 JMH Associates © 2004, All rights reserved FILE POINTERS (2 of 4) Note: NTFS is a 64-bit file system, so file pointers are 64 bits long. The file pointer is specified with two 32-bit parts.  Large files are increasingly important in many applications  But many users will only require “short” (< 4GB) files SetFilePointer Parameters hFile — Handle of an open file with read and/or write access lDistanceToMove — LONG signed distance to move or unsigned file position

48 JMH Associates © 2004, All rights reserved FILE POINTERS (3 of 4) * lpDistanceToMoveHigh  High-order portion of the move distance  Can be NULL for “small” files dwMoveMethod — Specifies one of these modes:  FILE_BEGIN — Position from the start of file  FILE_CURRENT — Move pointer forward or backward  FILE_END — Position backward from end of file SetEndOfFile () function resizes the file based on the current file pointer

49 JMH Associates © 2004, All rights reserved FILE POINTERS (4 of 4) Use the LARGE_INTEGER data type (union) for 64-bit file positions Example coming up Members: LONGLONG Quadpart Do the 64-bit arithmetic here DWORD LowPart LONG HighPart

50 JMH Associates © 2004, All rights reserved Alternative Direct File Access Using the Overlapped Structure (1 of 2) Example: Use the Offset fields in the overlapped structure  OffsetLow order 32 bits  OffsetHighHigh order 32 bits  hEventMust be NULL. This field is used with asynchronous I/O  Two reserved fieldsDo not use!! The example shows how to update a record in a file

51 JMH Associates © 2004, All rights reserved Alternative Direct File Access Using the Overlapped Structure (2 of 2) OVERLAPPED ov = { 0, 0, 0, 0, NULL }; RECORD r; /* Includes “reference count” field */ LONGLONG n; LARGE_INTEGER FilePos; DWORD nRd, nWrt;... /* Update reference count in the n’th record. */ FilePos.QuadPart = n * sizeof (RECORD); ov.Offset = FilePos.LowPart; ov.OffsetHigh = FilePos.HighPart; ReadFile (hFile, &r, sizeof(RECORD), &nRd, &ov); r.RefCount++; /* Update the record. */ WriteFile(hFile, &r, sizeof(RECORD), &nWrt, &ov);

52 JMH Associates © 2004, All rights reserved TOPIC VI File Locking

53 JMH Associates © 2004, All rights reserved FILE LOCKING (1 of 5)  Lock all or part of a file  Lock can be read-only (sharable) or read-write (exclusive)  Lock belongs to a process  Any attempt to access part of a file (using ReadFile or WriteFile ) in violation of a lock will fail  You cannot create conflicting locks on a file  Specify whether you should wait for a lock to become available, or thread can return immediately, indicating whether it obtained the lock

54 JMH Associates © 2004, All rights reserved FILE LOCKING (2 of 5) BOOL LockFileEx (HANDLE hFile, DWORD dwFlags, DWORD dwReserved, DWORD nNumberOfBytesToLockLow, DWORD nNumberOfBytesToLockHigh, LPOVERLAPPED lpOverlapped)  Locks a byte range in an open file for shared (multiple readers) or exclusive (one reader-writer) access

55 JMH Associates © 2004, All rights reserved FILE LOCKING (3 of 5) Parameters  hFile — Handle of an open file which must have at least one of GENERIC_READ or GENERIC_WRITE access  dwFlags — Determines the lock mode and whether to wait for the lock to become available  LOCKFILE_EXCLUSIVE_LOCK, if set, indicates a request for an exclusive, read-write, lock; otherwise, it requests a shared (read only) lock  LOCKFILE_FAIL_IMMEDIATELY, if set, specifies that the function should return immediately with a FALSE if the lock cannot be acquired; otherwise, the call blocks until the lock becomes available

56 JMH Associates © 2004, All rights reserved FILE LOCKING (4 of 5)  dwReserved must be zero  lpOverlapped — Points to an OVERLAPPED data structure containing the start of the byte range  The OVERLAPPED structure contains two data members that must be set (the others are ignored), namely:  DWORD Offset and  DWORD OffsetHigh A file lock is removed with a corresponding UnlockFileEx call, using all the same parameters except for dwFlags

57 JMH Associates © 2004, All rights reserved FILE LOCKING (5 of 5) BOOL UnlockFileEx (HANDLE hFile, DWORD dwReserved, DWORD nNumberOfBytesToLockLow, DWORD nNumberOfBytesToLockHigh, LPOVERLAPPED lpOverlapped)

58 JMH Associates © 2004, All rights reserved FILE LOCKING IN WINDOWS 9x Exclusive locks only BOOL LockFile (HANDLE hFile, DWORD dwOffsetLow, DWORD dwOffsetHigh DWORD nNumberOfBytesToLockLow, DWORD nNumberOfBytesToLockHigh) BOOL UnlockFile (HANDLE hFile, DWORD dwOffsetLow, DWORD dwOffsetHigh DWORD nNumberOfBytesToLockLow, DWORD nNumberOfBytesToLockHigh)

59 JMH Associates © 2004, All rights reserved FILE LOCKING CONSIDERATIONS  The unlock must use exactly the same range as a preceding lock  Locks cannot overlap existing locked regions in a file  You can lock beyond the range of a file’s length  Locks are not inherited by a newly created process

60 JMH Associates © 2004, All rights reserved LOCK REQUEST LOGIC Requested Lock Type Existing LockShared LockExclusive Lock None GrantedGranted Shared Lock GrantedRefused (one or more) Exclusive Lock RefusedRefused

61 JMH Associates © 2004, All rights reserved I/O Operation Existing LockReadWrite None SucceedsSucceeds Shared Lock Succeeds. It is notRefused (one or more) necessary for the calling process to own a lock on the file region. Exclusive Lock Succeeds if the calling process owns the lock. Fails otherwise. LOCKS AND I/O OPERATION

62 JMH Associates © 2004, All rights reserved FILE LOCKS—SUMMARY (1 of 2)  A failed read or write may take the form of a partially complete operation if only a portion of the read or write record is locked  Read and write operations are normally in the form of ReadFile and WriteFile calls, or ReadFileEx and WriteFileEx  Diagnosing a read or write failure requires calling GetLastError  Accessing memory that is mapped to a file is another form of file I/O

63 JMH Associates © 2004, All rights reserved FILE LOCKS—SUMMARY (2 of 2)  Lock conflicts are not detected at the time of memory reference; rather, they are detected at the time MapViewOfFile is called  The LockFile function is a limited, special case which gives exclusive access and returns immediately

64 JMH Associates © 2004, All rights reserved Part VII File and Directory Management

65 JMH Associates © 2004, All rights reserved FILE AND DIRECTORY MANAGEMENT BOOL DeleteFile (LPCTSTR lpFileName) You cannot delete an open file in Windows NT (You can in Windows 9x)

66 JMH Associates © 2004, All rights reserved FILE AND DIRECTORY MANAGEMENT—RENAMING (1 of 2) BOOL MoveFile (LPCTSTR lpExisting, LPCTSTR lpNew)  Source and target files must be on the same drive BOOL MoveFileEx (LPCTSTR lpExisting, LPCTSTR lpNew, DWORD dwFlags)  Source and target files can be on different drives Note: There are no links as in UNIX  Neither soft links nor hard links  Shortcuts are not the same thing; they are only recognized by the visual shell

67 JMH Associates © 2004, All rights reserved FILE AND DIRECTORY MANAGEMENT—RENAMING (2 of 2) Parameters lpExisting — The name of the existing file or directory lpNew — Cannot exist with MoveFile  Must be on same drive dwFlags  MOVEFILE_REPLACE_EXISTING  To replace an existing file  MOVEFILE_COPY_ALLOWED  Copy then delete

68 JMH Associates © 2004, All rights reserved DIRECTORY MANAGEMENT (1 of 4) BOOL CreateDirectory (LPCTSTR lpPath, LPSECURITY_ATTRIBUTES lpsa) BOOL RemoveDirectory (LPCTSTR lpPath) lpPath  Points to a null-terminated string with the directory name

69 JMH Associates © 2004, All rights reserved DIRECTORY MANAGEMENT (2 of 4) BOOL SetCurrentDirectory (LPCTSTR lpCurDir) lpCurDir  The path to the new current directory There is actually a current directory maintained for each drive SetCurrentDirectory (TEXT("C:"));  Will set the C: drive directory to its current value

70 JMH Associates © 2004, All rights reserved DIRECTORY MANAGEMENT (3 of 4) DWORD GetCurrentDirectory (DWORD cchCurDir, LPTSTR lpCurDir) Return:  The string length of the returned pathname  The required buffer size if the buffer is not large enough  This includes the space for the null string terminator  Zero if the function fails

71 JMH Associates © 2004, All rights reserved DIRECTORY MANAGEMENT (4 of 4) Windows uses this technique whenever the result’s length is not known Parameters cchCurDir  Character length of the buffer for the directory name  cch - “Count in characters” lpCurDir  Points to the buffer to receive the pathname string

72 JMH Associates © 2004, All rights reserved TESTING GetCurrentDirectory FOR CORRECT OPERATION /* pwd: Print the working directory. Similar to the UNIX pwd command */ /* This program illustrates: 1. Windows GetCurrentDirectory 2. Testing the length of a returned string */ #include "EvryThng.h" #define DIRNAME_LEN MAX_PATH + 2 int main (int argc, LPCTSTR argv []) { /* Buffer to receive current directory allows CR/LF at the end of the longest possible path. */ TCHAR pwdBuffer [DIRNAME_LEN];

73 JMH Associates © 2004, All rights reserved GetCurrentDirectory (2 of 2) DWORD LenCurDir; LenCurDir = GetCurrentDirectory (DIRNAME_LEN, pwdBuffer); if (LenCurDir == 0) ReportError (TEXT ("Failure getting pathname\n"), 1, TRUE); if (LenCurDir > DIRNAME_LEN) ReportError (TEXT ("Pathname is too long\n"), 2, FALSE); PrintMsg (GetStdHandle (STD_OUTPUT_HANDLE), pwdBuffer); return 0; }

74 JMH Associates © 2004, All rights reserved FILE ATTRIBUTES AND FILE SEARCHING (1 of 2) HANDLE FindFirstFile (LPCTSTR lpSearchFile, LPWIN32_FIND_DATA lpffd) Return: A “search handle”  INVALID_HANDLE_VALUE indicates failure Parameters  lpSearchFile — Points to directory or pathname. Wildcards are OK ( * and ? )  lpffd — Points to a WIN32_FIND_DATA structure

75 JMH Associates © 2004, All rights reserved FILE ATTRIBUTES AND FILE SEARCHING (2 of 2) typedef struct _WIN32_FIND_DATA { DWORD dwFileAttributes; /* see CreateFile */ FILETIME ftCreationTime; /* 64-bit int */ FILETIME ftLastAccessTime; FILETIME ftLastWriteTime; DWORD nFileSizeHigh; DWORD nFileSizeLow; DWORD dwReserved0; DWORD dwReserved1; TCHAR cFileName [MAX_PATH]; /* file name */ TCHAR cAlternateFileName [14]; /* 8.3 name */ } WIN32_FIND_DATA;

76 JMH Associates © 2004, All rights reserved FILES AND DIRECTORIES (1 of 5) BOOL FindNextFile (HANDLE hFindFile, LPWIN32_FIND_DATA lpffd)  FALSE when no more files satisfy the search pattern BOOL FindClose (HANDLE hFindFile)  Exception: This is an example of a HANDLE that is not closed with CloseHandle.

77 JMH Associates © 2004, All rights reserved FILES AND DIRECTORYS (2 of 5) File attributes can be obtained individually  Usually from the HANDLE rather than file name DWORD GetFileSize (HANDLE hFile, LPDWORD lpdwFileSizeHigh) Return: The low-order component of the file size  0xFFFFFFFF indicates a possible error; check GetLastError

78 JMH Associates © 2004, All rights reserved FILES AND DIRECTORYS (3 of 5) DWORD GetFileInformationByHandle (HANDLE hFile) Use GetCompressedFileSize to test for an empty file  if you have the file name but do not have an open handle

79 JMH Associates © 2004, All rights reserved FILES AND DIRECTORYS (4 of 5) BOOL GetFileTime (HANDLE hFile, LPFILETIME lpftCreation, LPFILETIME lpftLastAccess, LPFILETIME lpftLastWrite) BOOL FileTimeToSystemTime( CONST FILETIME * lpFileTime, LPSYSTEMTIME lpSystemTime) LPSYSTEMTIME has WORD members for the time components:  wYear, wMonth, …, wMilliseconds FILETIME (64 bits) is elapsed 100 ns units since Jan 1, 1601  More than 60,000 years can be represented

80 JMH Associates © 2004, All rights reserved FILES AND DIRECTORYS (5 of 5) DWORD GetFileAttributes (LPCTSTR lpFileName) Return: The file attributes or 0xFFFFFFFF in case of failure  The attributes can be tested for the following values:  FILE_ATTRIBUTE_DIRECTORY  FILE_ATTRIBUTE_NORMAL  FILE_ATTRIBUTE_READONLY  FILE_ATTRIBUTE_TEMPORARY SetFileAttributes  Allows you to change attributes in a named file

81 JMH Associates © 2004, All rights reserved TEMPORARY FILE NAMES (1 of 2) UINT GetTempFileName (LPCTSTR lpPath, LPCTSTR lpPrefix, UINT uUnique, LPTSTR lpTempFile) Return: A unique numeric value used to create the file name  uUnique if uUnique is non-zero  On failure, the return value is zero.

82 JMH Associates © 2004, All rights reserved TEMPORARY FILE NAMES (2 of 2) lpPath  Directory where you want the temporary file lpPrefix  Prefix of the temporary name uUnique  Normally zero to generate a unique four-digit suffix lpTempFile  Points to buffer for the temporary file name

83 JMH Associates © 2004, All rights reserved LAB 3–B (Option 1) Option 1 Create a program, pwdA, based on the existing pwd so that you do not need to know the maximum pathname length ahead of time Determine the number of characters in the current directory, allocate the required memory, and then call GetCurrentDirectory () a second time Note: This option is easy; you should select another one as well.

84 JMH Associates © 2004, All rights reserved LAB 3–B (Options 2 and 3) Option 2 (file attributes and directory scanning) Create a program, ls, to list the attributes (size and times) of each file and directory, starting at a specified path Option 3 (direct file access) Write a program, tail, that will display the last ten lines of a text file