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1JMH Associates © 2004, All rights reserved
Chapters 2-3Chapters 2-3Chapters 2-3Chapters 2-3
Input/Output
With File and Directory Processing
2JMH Associates © 2004, All rights reserved
OBJECTIVES (1 of 2)OBJECTIVES (1 of 2)OBJECTIVES (1 of 2)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
3JMH Associates © 2004, All rights reserved
OBJECTIVES (2 of 2)OBJECTIVES (2 of 2)OBJECTIVES (2 of 2)OBJECTIVES (2 of 2)
You will also be prepared for later Chapters Memory-mapped files Process management Interprocess communication Threads Synchronization Asynchronous I/O
4JMH Associates © 2004, All rights reserved
AGENDAAGENDAAGENDAAGENDA
Part I File Systems and Sequential I/O
Part II Unicode and Generic Characters
Part III Console I/O
Part IV Lab 2–A
Part V Direct File Access
Part VI File Locking
Part VII File and Directory ManagementLab 3–B
5JMH Associates © 2004, All rights reserved
Part IPart IPart IPart I
File Systems and Sequential I/O
6JMH Associates © 2004, All rights reserved
BASIC I/OBASIC I/OBASIC I/OBASIC I/O
Basic Windows API file processing functions:
CreateFile
ReadFile
WriteFile
CloseHandle
We used these, in a very simple program, in Chapter 1
7JMH Associates © 2004, All rights reserved
THE FILE SYSTEMSTHE FILE SYSTEMSTHE FILE SYSTEMSTHE 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
8JMH Associates © 2004, All rights reserved
Windows FILE NAMING (1 of 2)Windows FILE NAMING (1 of 2)Windows FILE NAMING (1 of 2)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
9JMH Associates © 2004, All rights reserved
Windows FILE NAMING (2 of 2)Windows FILE NAMING (2 of 2)Windows FILE NAMING (2 of 2)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
10JMH Associates © 2004, All rights reserved
CREATING AND OPENING FILESCREATING AND OPENING FILESCREATING AND OPENING FILESCREATING 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
11JMH Associates © 2004, All rights reserved
CREATING AND OPENING FILESCREATING AND OPENING FILES(2 OF 6)(2 OF 6)
CREATING AND OPENING FILESCREATING AND OPENING FILES(2 OF 6)(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 |
12JMH Associates © 2004, All rights reserved
CREATING AND OPENING (3 OF 6)CREATING AND OPENING (3 OF 6)CREATING AND OPENING (3 OF 6)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
13JMH Associates © 2004, All rights reserved
CREATING AND OPENING (4 OF 6)CREATING AND OPENING (4 OF 6)CREATING AND OPENING (4 OF 6)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
14JMH Associates © 2004, All rights reserved
CREATING AND OPENING (5 OF 6)CREATING AND OPENING (5 OF 6)CREATING AND OPENING (5 OF 6)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 themselvesFlags are associated with a specific HANDLE
Different HANDLEs 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
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CREATING AND OPENING (6 OF 6)CREATING AND OPENING (6 OF 6)CREATING AND OPENING (6 OF 6)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
16JMH Associates © 2004, All rights reserved
READING FILES (1 OF 2)READING FILES (1 OF 2)READING FILES (1 OF 2)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.
17JMH Associates © 2004, All rights reserved
READING FILES (2 OF 2)READING FILES (2 OF 2)READING FILES (2 OF 2)READING FILES (2 OF 2)
Parameters
hFile — File handle with GENERIC_READ access
lpBuffer — Memory 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)
18JMH Associates © 2004, All rights reserved
WRITING FILESWRITING FILESWRITING FILESWRITING FILES
BOOL WriteFile (HANDLE hFile, CONST VOID *lpBuffer,DWORD nNumberOfBytesToWrite,LPDWORD lpNumberOfBytesWritten,LPOVERLAPPED lpOverlapped)
Return: TRUE if the function succeeds; FALSE otherwise
19JMH Associates © 2004, All rights reserved
CLOSING FILESCLOSING FILESCLOSING FILESCLOSING 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
20JMH Associates © 2004, All rights reserved
COPYING FILESCOPYING FILESCOPYING FILESCOPYING 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
21JMH Associates © 2004, All rights reserved
Part IIPart IIPart IIPart II
Unicode and Generic Characters
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UNICODE & GENERIC CHARACTERSUNICODE & GENERIC CHARACTERSUNICODE & GENERIC CHARACTERSUNICODE & 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” typeTCHAR
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 <windows.h>
Also define _UNICODE consistently for the generic C library
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GENERIC CHARACTERS (2 of 3)GENERIC CHARACTERS (2 of 3)GENERIC CHARACTERS (2 of 3)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
24JMH Associates © 2004, All rights reserved
GENERIC CHARACTERS (3 of 3)GENERIC CHARACTERS (3 of 3)GENERIC CHARACTERS (3 of 3)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 *
25JMH Associates © 2004, All rights reserved
THE GENERIC C LIBRARYTHE GENERIC C LIBRARYTHE GENERIC C LIBRARYTHE 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 <tchar.h> after <windows.h>
Note: Any _ keyword or function is specific to Microsoft Visual C++ and the Microsoft compiler
26JMH Associates © 2004, All rights reserved
GENERIC CHARACTERS AND THE GENERIC CHARACTERS AND THE MAIN PROGRAMMAIN PROGRAM
GENERIC CHARACTERS AND THE GENERIC CHARACTERS AND THE MAIN PROGRAMMAIN 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 <tchar.h>
/* this is after <windows.h> */
... 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
27JMH Associates © 2004, All rights reserved
Part IIIPart IIIPart IIIPart III
Standard Devices and Console I/O
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STANDARD DEVICESSTANDARD DEVICESAND CONSOLE I/O (1 of 7)AND CONSOLE I/O (1 of 7)
STANDARD DEVICESSTANDARD DEVICESAND CONSOLE I/O (1 of 7)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
29JMH Associates © 2004, All rights reserved
STANDARD DEVICESSTANDARD DEVICESAND CONSOLE I/O (2 of 7)AND CONSOLE I/O (2 of 7)
STANDARD DEVICESSTANDARD DEVICESAND CONSOLE I/O (2 of 7)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
30JMH Associates © 2004, All rights reserved
STANDARD DEVICESSTANDARD DEVICESAND CONSOLE I/O (3 of 7)AND CONSOLE I/O (3 of 7)
STANDARD DEVICESSTANDARD DEVICESAND CONSOLE I/O (3 of 7)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"
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STANDARD DEVICESSTANDARD DEVICESAND CONSOLE I/O (4 of 7)AND CONSOLE I/O (4 of 7)
STANDARD DEVICESSTANDARD DEVICESAND CONSOLE I/O (4 of 7)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
32JMH Associates © 2004, All rights reserved
STANDARD DEVICESSTANDARD DEVICESAND CONSOLE I/O (5 of 7)AND CONSOLE I/O (5 of 7)
STANDARD DEVICESSTANDARD DEVICESAND CONSOLE I/O (5 of 7)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
33JMH Associates © 2004, All rights reserved
STANDARD DEVICESSTANDARD DEVICESAND CONSOLE I/O (6 of 7)AND CONSOLE I/O (6 of 7)
STANDARD DEVICESSTANDARD DEVICESAND CONSOLE I/O (6 of 7)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
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STANDARD DEVICESSTANDARD DEVICESAND CONSOLE I/O (7 of 7)AND CONSOLE I/O (7 of 7)
STANDARD DEVICESSTANDARD DEVICESAND CONSOLE I/O (7 of 7)AND CONSOLE I/O (7 of 7)
BOOL WriteConsole Same as ReadConsole
BOOL FreeConsole (VOID)
BOOL AllocConsole (VOID)
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EXAMPLE: EXAMPLE: PrintStringsPrintStrings (1 of 3) (1 of 3)EXAMPLE: EXAMPLE: PrintStringsPrintStrings (1 of 3) (1 of 3)
#include "envirmnt.h" /* UNICODE is defined here */#include <windows.h>
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. */
36JMH Associates © 2004, All rights reserved
PrintStringsPrintStrings (2 of 3) (2 of 3)PrintStringsPrintStrings (2 of 3) (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)
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PrintStringsPrintStrings (3 of 3) (3 of 3)PrintStringsPrintStrings (3 of 3) (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;}
38JMH Associates © 2004, All rights reserved
EXAMPLE: EXAMPLE: ReportErrorReportError (1 of 4) (1 of 4)EXAMPLE: EXAMPLE: ReportErrorReportError (1 of 4) (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.
39JMH Associates © 2004, All rights reserved
EXAMPLE: EXAMPLE: ReportErrorReportError (2 of 4) (2 of 4)EXAMPLE: EXAMPLE: ReportErrorReportError (2 of 4) (2 of 4)
#include "envirmnt.h"#include <windows.h>#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. */
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ReportErrorReportError (3 of 4) (3 of 4)ReportErrorReportError (3 of 4) (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) {
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ReportErrorReportError (4 of 4) (4 of 4)ReportErrorReportError (4 of 4) (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;}
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LAB 2–A (Option 1)LAB 2–A (Option 1)LAB 2–A (Option 1)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.
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LAB 2–A (Option 2)LAB 2–A (Option 2)LAB 2–A (Option 2)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.
44JMH Associates © 2004, All rights reserved
LAB 2–A (Option 3)LAB 2–A (Option 3)LAB 2–A (Option 3)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).
45JMH Associates © 2004, All rights reserved
Part VPart VPart VPart V
Direct File Access
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FILE POINTERS (1 of 4)FILE POINTERS (1 of 4)FILE POINTERS (1 of 4)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.
47JMH Associates © 2004, All rights reserved
FILE POINTERS (2 of 4)FILE POINTERS (2 of 4)FILE POINTERS (2 of 4)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
48JMH Associates © 2004, All rights reserved
FILE POINTERS (3 of 4)FILE POINTERS (3 of 4)FILE POINTERS (3 of 4)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
49JMH Associates © 2004, All rights reserved
FILE POINTERS (4 of 4)FILE POINTERS (4 of 4)FILE POINTERS (4 of 4)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 hereDWORD LowPartLONG HighPart
50JMH Associates © 2004, All rights reserved
Alternative Direct File Access Using Alternative Direct File Access Using the Overlapped Structure (1 of 2)the Overlapped Structure (1 of 2)
Alternative Direct File Access Using Alternative Direct File Access Using the Overlapped Structure (1 of 2)the Overlapped Structure (1 of 2)
Example: Use the Offset fields in the overlapped structure Offset Low order 32 bits OffsetHigh High order 32 bits hEvent Must be NULL. This field is
used with asynchronous I/O
Two reserved fields Do not use!!
The example shows how to update a record in a file
51JMH Associates © 2004, All rights reserved
Alternative Direct File Access Using Alternative Direct File Access Using the Overlapped Structure (2 of 2)the Overlapped Structure (2 of 2)
Alternative Direct File Access Using Alternative Direct File Access Using the Overlapped Structure (2 of 2)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);
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TOPIC VITOPIC VITOPIC VITOPIC VI
File Locking
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FILE LOCKING (1 of 5)FILE LOCKING (1 of 5)FILE LOCKING (1 of 5)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
54JMH Associates © 2004, All rights reserved
FILE LOCKING (2 of 5)FILE LOCKING (2 of 5)FILE LOCKING (2 of 5)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
55JMH Associates © 2004, All rights reserved
FILE LOCKING (3 of 5)FILE LOCKING (3 of 5)FILE LOCKING (3 of 5)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
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FILE LOCKING (4 of 5)FILE LOCKING (4 of 5)FILE LOCKING (4 of 5)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
57JMH Associates © 2004, All rights reserved
FILE LOCKING (5 of 5)FILE LOCKING (5 of 5)FILE LOCKING (5 of 5)FILE LOCKING (5 of 5)
BOOL UnlockFileEx (HANDLE hFile,DWORD dwReserved,DWORD nNumberOfBytesToLockLow,DWORD nNumberOfBytesToLockHigh,LPOVERLAPPED lpOverlapped)
58JMH Associates © 2004, All rights reserved
FILE LOCKING IN WINDOWS 9xFILE LOCKING IN WINDOWS 9xFILE LOCKING IN WINDOWS 9xFILE LOCKING IN WINDOWS 9x
Exclusive locks only
BOOL LockFile (HANDLE hFile,DWORD dwOffsetLow, DWORD dwOffsetHighDWORD nNumberOfBytesToLockLow,DWORD nNumberOfBytesToLockHigh)
BOOL UnlockFile (HANDLE hFile,DWORD dwOffsetLow, DWORD dwOffsetHighDWORD nNumberOfBytesToLockLow,DWORD nNumberOfBytesToLockHigh)
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FILE LOCKING CONSIDERATIONSFILE LOCKING CONSIDERATIONSFILE LOCKING CONSIDERATIONSFILE 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
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LOCK REQUEST LOGICLOCK REQUEST LOGICLOCK REQUEST LOGICLOCK REQUEST LOGIC
Requested Lock Type
Existing Lock Shared LockExclusive Lock
None Granted Granted
Shared LockGranted Refused(one or more)
Exclusive Lock Refused Refused
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I/O Operation
Existing Lock Read Write
None Succeeds Succeeds
Shared LockSucceeds. It is not Refused(one or more) necessary for the calling
process to own a lockon the file region.
Exclusive Lock Succeeds if the calling process owns thelock. Fails otherwise.
LOCKS AND I/O OPERATIONLOCKS AND I/O OPERATIONLOCKS AND I/O OPERATIONLOCKS AND I/O OPERATION
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FILE LOCKS—SUMMARY (1 of 2)FILE LOCKS—SUMMARY (1 of 2)FILE LOCKS—SUMMARY (1 of 2)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
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FILE LOCKS—SUMMARY (2 of 2)FILE LOCKS—SUMMARY (2 of 2)FILE LOCKS—SUMMARY (2 of 2)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
64JMH Associates © 2004, All rights reserved
Part VIIPart VIIPart VIIPart VII
File and Directory Management
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FILE AND DIRECTORY MANAGEMENTFILE AND DIRECTORY MANAGEMENTFILE AND DIRECTORY MANAGEMENTFILE AND DIRECTORY MANAGEMENT
BOOL DeleteFile (LPCTSTR lpFileName)
You cannot delete an open file in Windows NT
(You can in Windows 9x)
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FILE AND DIRECTORY MANAGEMENTFILE AND DIRECTORY MANAGEMENT—RENAMING (1 of 2)—RENAMING (1 of 2)
FILE AND DIRECTORY MANAGEMENTFILE AND DIRECTORY MANAGEMENT—RENAMING (1 of 2)—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
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FILE AND DIRECTORY MANAGEMENTFILE AND DIRECTORY MANAGEMENT—RENAMING (2 of 2)—RENAMING (2 of 2)
FILE AND DIRECTORY MANAGEMENTFILE AND DIRECTORY MANAGEMENT—RENAMING (2 of 2)—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
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DIRECTORY MANAGEMENT (1 of 4)DIRECTORY MANAGEMENT (1 of 4)DIRECTORY MANAGEMENT (1 of 4)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
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DIRECTORY MANAGEMENT (2 of 4)DIRECTORY MANAGEMENT (2 of 4)DIRECTORY MANAGEMENT (2 of 4)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
70JMH Associates © 2004, All rights reserved
DIRECTORY MANAGEMENT (3 of 4)DIRECTORY MANAGEMENT (3 of 4)DIRECTORY MANAGEMENT (3 of 4)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
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DIRECTORY MANAGEMENT (4 of 4)DIRECTORY MANAGEMENT (4 of 4)DIRECTORY MANAGEMENT (4 of 4)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
72JMH Associates © 2004, All rights reserved
TESTING TESTING GetCurrentDirectoryGetCurrentDirectory FOR FOR CORRECT OPERATIONCORRECT OPERATION
TESTING TESTING GetCurrentDirectoryGetCurrentDirectory FOR FOR CORRECT OPERATIONCORRECT 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 + 2int 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];
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GetCurrentDirectoryGetCurrentDirectory (2 of 2) (2 of 2)GetCurrentDirectoryGetCurrentDirectory (2 of 2) (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;}
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FILE ATTRIBUTES ANDFILE ATTRIBUTES ANDFILE SEARCHING (1 of 2)FILE SEARCHING (1 of 2)FILE ATTRIBUTES ANDFILE ATTRIBUTES AND
FILE SEARCHING (1 of 2)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
75JMH Associates © 2004, All rights reserved
FILE ATTRIBUTES ANDFILE ATTRIBUTES ANDFILE SEARCHING (2 of 2)FILE SEARCHING (2 of 2)FILE ATTRIBUTES ANDFILE ATTRIBUTES AND
FILE SEARCHING (2 of 2)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;
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FILES AND DIRECTORIES (1 of 5)FILES AND DIRECTORIES (1 of 5)FILES AND DIRECTORIES (1 of 5)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.
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FILES AND DIRECTORYS (2 of 5)FILES AND DIRECTORYS (2 of 5)FILES AND DIRECTORYS (2 of 5)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
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FILES AND DIRECTORYS (3 of 5)FILES AND DIRECTORYS (3 of 5)FILES AND DIRECTORYS (3 of 5)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
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FILES AND DIRECTORYS (4 of 5)FILES AND DIRECTORYS (4 of 5)FILES AND DIRECTORYS (4 of 5)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
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FILES AND DIRECTORYS (5 of 5)FILES AND DIRECTORYS (5 of 5)FILES AND DIRECTORYS (5 of 5)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
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TEMPORARY FILE NAMES (1 of 2)TEMPORARY FILE NAMES (1 of 2)TEMPORARY FILE NAMES (1 of 2)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.
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TEMPORARY FILE NAMES (2 of 2)TEMPORARY FILE NAMES (2 of 2)TEMPORARY FILE NAMES (2 of 2)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
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LAB 3–B (Option 1)LAB 3–B (Option 1)LAB 3–B (Option 1)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.
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LAB 3–B (Options 2 and 3)LAB 3–B (Options 2 and 3)LAB 3–B (Options 2 and 3)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