DosOpen

This call opens a new file, an existing file, a replacement for an existing file, a named pipe, or a device.

DosOpen (FileName, FileHandle, ActionTaken,
          FileSize, FileAttribute, OpenFlag, OpenMode, Reserved)

• FileName (PSZ) - input : Address of the ASCIIZ path name of the file, named pipe, or device to be opened.
• FileHandle (PHFILE) - output : Address of the handle for the file, named pipe, or device.
• ActionTaken (PUSHORT) - output : Address of the action taken as a result of DosOpen.

• FileSize (ULONG) - input : File's new logical size (EOD), in bytes. This parameter is significant only when creating a new file or replacing an existing file. Otherwise, it is ignored.
• FileAttribute (USHORT) - input : File attribute bits.

Defined below:

These bits may be set individually or in combination. For example, an attribute value of 0021H (bits 5 and 0 set to 1) indicates a read-only file that should be archived.

• OpenFlag (USHORT) - input : One-word field indicates the action to be taken if the file exists or does not exist.

• OpenMode (USHORT) - input : The OpenMode parameter contains the following bit flags:

Any other value is invalid.

Any other combinations are invalid.

File sharing requires the cooperation of sharing processes. This cooperation is communicated through sharing and access modes. Any sharing restrictions placed on a file opened by a process are removed when the process closes the file with a DosClose request.

Specify the type of access other processes may have to the file (sharing mode). For example, if it is permissible for other processes to continue reading the file while your process is operating on it, specify Deny Write. This sharing mode prevents other processes from writing to the file but still allows them to read it.

Specify the type of access to the file needed by your process (access mode).

For example, if your process requires Read/Write access, and another process has already opened the file with a sharing mode of Deny None, your DosOpen request succeeds. However, if the file is open with a sharing mode of Deny Write, your process is denied access.

If the file is inherited by a child process, all sharing and access restrictions are also inherited.

If an open file handle is duplicated by a call to DosDupHandle, all sharing and access restrictions are also duplicated.

• Reserved (ULONG) - input : Reserved and must be set to zero.

rc (USHORT) - return

Return code descriptions are:

• 0 NO_ERROR
• 2 ERROR_FILE_NOT_FOUND
• 3 ERROR_PATH_NOT_FOUND
• 4 ERROR_TOO_MANY_OPEN_FILES
• 5 ERROR_ACCESS_DENIED
• 12 ERROR_INVALID_ACCESS
• 26 ERROR_NOT_DOS_DISK
• 32 ERROR_SHARING_VIOLATION
• 36 ERROR_SHARING_BUFFER_EXCEEDED
• 82 ERROR_CANNOT_MAKE
• 87 ERROR_INVALID_PARAMETER
• 108 ERROR_DRIVE_LOCKED
• 110 ERROR_OPEN_FAILED
• 112 ERROR_DISK_FULL
• 206 ERROR_FILENAME_EXCED_RANGE
• 231 ERROR_PIPE_BUSY
• 99 ERROR_DEVICE_IN_USE

A successful DosOpen request for a file returns a handle to access the file. The read/write pointer is set at the first byte of the file. The pointer's position may be changed by a DosChgFilePtr request or by read and write operations on the file.

The file's date and time can be queried by calling DosQFileInfo, and set by calling DosSetFileInfo.

FileAttribute sets attribute bits for the file object. Attributes of an existing file can be queried and set by DosQFileMode and DosSetFileMode. A file's read-only attribute may also be set with the OS/2 ATTRIB command.

FileAttribute cannot be set to Volume Label. Volume labels cannot be opened. DosSetFSInfo may be issued with a logical drive number to set volume label information.

The FileSize parameter affects the size of the file only when the file is a new file or a replacement for an existing one. If an existing file is simply opened, FileSize is ignored. DosNewSize may be called to change the existing file's size.

The value in FileSize is a recommended size for the file. If allocation of the full size fails, the open may still succeed. The file system makes a reasonable attempt to allocate the new size in as nearly contiguous an area as possible on the medium. When the file size is extended, the value of the new bytes is undefined.

The DASD Open bit provides direct access to an entire disk or diskette volume, independent of the file system. This mode of opening the volume currently mounted on the drive returns a handle to the caller, which represents the logical volume as a single file. The caller specifies this handle with a DosDevIOCtl Category 8 Function 0 request to block other processes from accessing the logical volume.

The file handle state bits can be set by the DosOpen and DosSetFHandState requests. An application can query the file handle state bits as well as the rest of the Open Mode field, by calling DosQFHandState. If a program running with the NEWFILES bit set tries to create or replace a file with blanks immediately preceding the dot on a FAT drive, the system rejects the name. For example, if c: is a FAT drive, the name “file .txt” is rejected and the name “file.txt” is accepted.

Some options operate differently in the DOS mode than in the OS/2 mode. Therefore, the following restrictions apply to DosOpen when coding for the DOS mode:

OpenMode restrictions:

• Handles returned in response to DASD open are valid only for DosDevIOCtl.
• Inheritance flag is not supported in DOS 2.X.
• Write-Through flag must be set to zero.
• Fail-errors flag must be set to zero.
• Sharing mode field has meaning only if Sharing is loaded in DOS 3.X, ignored if Sharing is not loaded. Sharing mode is not supported in DOS 2.X.
• Access mode field has meaning only if Sharing is loaded in DOS 3.X, ignored if Sharing is not loaded. Access mode field is not supported in DOS 2.X.
• Access mode is valid only if Sharing is loaded.

DosOpen opens the client end of a pipe by name and returns a handle. The open succeeds only if the pipe is in a listening state; otherwise, the open returns with ERROR_PIPE_BUSY. The pipe can be busy because of the following reasons: * All instances of the pipe are already open. * The pipe is closed but is not yet disconnected by the serving end. * No DosConnectNmPipe is issued against the pipe after it is disconnected.

Once a given instance has been opened by a client, that same instance cannot be opened by another client at the same time. Pipes can only be two-ended; however, the opening process can duplicate the open handle as many times as desired.

Pipes are always opened with the pipe-specific states set to B = 0 (to block reads/writes) and RR = 00 (read the pipe as a byte stream). The client can change these modes by calling DosSetNmPHandState if desired.

The access and sharing modes specified on the open must be consistent with those specified on the DosMakeNmPipe request.

#define INCL_DOSFILEMGR
 
USHORT  rc = DosOpen(FileName, FileHandle, ActionTaken, FileSize,
                             FileAttribute, OpenFlag, OpenMode, Reserved);
 
PSZ              FileName;      /* File path name string */
PHFILE           FileHandle;    /* File handle (returned) */
PUSHORT          ActionTaken;   /* Action taken (returned) */
ULONG            FileSize;      /* File primary allocation */
USHORT           FileAttribute; /* File Attribute */
USHORT           OpenFlag;      /* Open function type */
USHORT           OpenMode;      /* Open mode of the file */
ULONG            0;             /* Reserved (must be zero) */
 
USHORT           rc;            /* return code */

EXTRN  DosOpen:FAR
INCL_DOSFILEMGR     EQU 1
 
PUSH@  ASCIIZ  FileName      ;File path name string
PUSH@  WORD    FileHandle    ;File handle (returned)
PUSH@  WORD    ActionTaken   ;Action taken (returned)
PUSH   DWORD   FileSize      ;File primary allocation
PUSH   WORD    FileAttribute ;File Attribute
PUSH   WORD    OpenFlag      ;Open function type
PUSH   WORD    OpenMode      ;Open mode of the file
PUSH   DWORD   0             ;Reserved (must be zero)
CALL   DosOpen
 
Returns WORD

This example opens a file.

#define INCL_DOSFILEMGR
 
#define OPEN_FILE 0x01
#define CREATE_FILE 0x10
#define FILE_ARCHIVE 0x20
#define FILE_EXISTS OPEN_FILE
#define FILE_NOEXISTS CREATE_FILE
#define DASD_FLAG 0
#define INHERIT 0x80
#define WRITE_THRU 0
#define FAIL_FLAG 0
#define SHARE_FLAG 0x10
#define ACCESS_FLAG 0x02
 
#define FILE_NAME "test.dat"
#define FILE_SIZE 800L
#define FILE_ATTRIBUTE FILE_ARCHIVE
#define RESERVED 0L
 
HFILE   FileHandle;
USHORT  Wrote;
USHORT  Action;
PSZ     FileData[100];
USHORT  rc;
 
   Action = 2;
   strcpy(FileData, "Data...");
   rc = DosOpen(FILE_NAME,               /* File path name */
                &FileHandle,             /* File handle */
                &Action,                 /* Action taken */
                FILE_SIZE,               /* File primary allocation */
                FILE_ATTRIBUTE,          /* File attribute */
                FILE_EXISTS | FILE_NOEXISTS,     /* Open Function type */
                DASD_FLAG | INHERIT |            /* Open mode of the file */
                WRITE_THRU | FAIL_FLAG |
                SHARE_FLAG | ACCESS_FLAG,
                RESERVED);               /* Reserved (must be zero) */

Text based on http://www.edm2.com/index.php/DosOpen_(FAPI)