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35    File Streaming

Palm OS® Programmer's API Reference

Palm OS® 68K SDK

     

This chapter provides reference material for the file streaming API.

The header file FileStream.h declares the API that this chapter describes. For more information on file streaming, see the chapter "Files and Databases" in the Palm OS Programmer's Companion, vol. I.

File Streaming Constants ^TOP^

Primary Open Mode Constants ^TOP^

This section lists constants passed in the openMode parameter to the FileOpen() function. These constants specify the mode in which a file stream is opened.

For each file stream, you must pass to the FileOpen() function only one of the primary mode selectors listed.

fileModeReadOnly
Open for read-only access
fileModeReadWrite
Open/create for read/write access, discarding any previous version of stream
fileModeUpdate
Open/create for read/write, preserving previous version of stream if it exists
fileModeAppend
Open/create for read/write, always writing to the end of the stream

Secondary Open Mode Constants ^TOP^

You can use the | operator (bitwise inclusive OR) to append to a primary mode selector one or more of the secondary mode selectors listed below.

fileModeDontOverwrite
Prevents fileModeReadWrite from discarding an existing stream having the same name; may only be specified together with fileModeReadWrite
fileModeLeaveOpen
Leave stream open when application quits. Most applications should not use this option.
fileModeExclusive
No other application can open the stream until the application that opened it in this mode closes it.
fileModeAnyTypeCreator
Accept any type/creator when opening or replacing an existing stream. Normally, the FileOpen() function opens only streams having the specified creator and type. Setting this option enables the FileOpen function to open streams having a type or creator other than those specified.
fileModeTemporary
Delete the stream automatically when it is closed. For more information, see Comment section of FileOpen() function description.

File Streaming Functions ^TOP^

FileClearerr Function ^TOP^

Purpose

Clear I/O error status, end of file error status, and last error.

Declared In

FileStream.h

Prototype

Err FileClearerr (
   FileHandstream
) 

Parameters

stream
Handle to open stream.

Returns

0 if no error, or a fileErr code if an error occurs. See the section "File Streaming Error Codes" for more information.

Compatibility

Implemented only if 3.0 New Feature Set is present.

See Also

FileGetLastError(), FileRewind()

FileClose Function ^TOP^

Purpose

Close the file stream and destroy its handle. If the stream was opened with fileModeTemporary, it is deleted upon closing.

Declared In

FileStream.h

Prototype

Err FileClose (
   FileHandstream
)

Parameters

stream
Handle to open stream.

Returns

0 if no error, or a fileErr code if an error occurs. See the section "File Streaming Error Codes" for more information.

Compatibility

Implemented only if 3.0 New Feature Set is present.

FileControl Function ^TOP^

Purpose

Perform the operation specified by the op parameter on the stream file stream.

Declared In

FileStream.h

Prototype

Err FileControl (
   FileOpEnumop,
   FileHandstream,
   void*valueP,
   Int32*valueLenP
)

Parameters

op
The operation to perform, and its associated formal parameters. See the Comments section for a list of possible values.
stream
Open stream handle if required for file stream operation.
valueP
Pointer to value or buffer, as required. This parameter is defined by the selector passed as the value of the op parameter. For details, see the Comments section.
valueLenP
Pointer to value or buffer, as required. This parameter is defined by the selector passed as the value of the op parameter. For details, see the Comments section.

Returns

Returns either a value defined by the selector passed as the argument to the op parameter, or an error code resulting from the requested operation. For details, see the Comments section.

Comments

Normally, you do not call the FileControl() function yourself; it is called for you by most of the other file streaming functions and macros to perform common file streaming operations. You can call FileControl() yourself to enable specialized read modes.

fileOpNone
No-op.
fileOpDestructiveReadMode
Enter destructive read mode, and rewind stream to its beginning. Once in this mode, there is no turning back: stream's contents after closing (or crash) are undefined.
Destructive read mode deletes blocks as data are read, thus freeing storage automatically. Once in destructive read mode, you cannot re-use the file stream—the contents of the stream are undefined after it is closed or after a crash.
Writing to files opened without write access or those that are in destructive read state is not allowed; thus, you cannot call the FileWrite(), FileSeek(), or FileTruncate() functions on a stream that is in destructive read mode. One exception to this rule applies to streams that were opened in "write + append" mode and then switched into destructive read state. In this case, the FileWrite() function can append data to the stream, but it also preserves the current stream position so that subsequent reads pick up where they left off (you can think of this as a pseudo-pipe).
ARGUMENTS:
stream = open stream handle
valueP = NULL
valueLenP = NULL
RETURNS:
zero on success;
fileErr... on error
fileOpGetEOFStatus
Get end-of-file status (like C runtime's feof) (err = fileErrEOF). Indicates end of file condition. Use FileClearerr() to clear this error status.
ARGUMENTS:
stream = open stream handle
valueP = NULL
valueLenP = NULL
RETURNS:
zero if not end of file;
non-zero if end of file
fileOpGetLastError
Get error code from last operation on stream, and clear the last error code value. Doesn't change status of EOF or I/O errors —use FileClearerr() to reset all error codes.
ARGUMENTS:
stream = open stream handle
valueP = NULL
valueLenP = NULL
RETURNS:
Error code from last file stream operation
fileOpClearError
Clear I/O and EOF error status and last error.
ARGUMENTS:
stream = open stream handle
valueP = NULL
valueLenP = NULL
RETURNS:
zero on success; fileErr... on error
fileOpGetIOErrorStatus
Get I/O error status (like C runtime's ferror). Use FileClearerr() to clear this error status.
ARGUMENTS:
stream = open stream handle
valueP = NULL
valueLenP = NULL
RETURNS:
zero if not I/O error;
non-zero if I/O error is pending.
fileOpGetCreatedStatus
Find out whether file was created by FileOpen() function
ARGUMENTS:
stream = open stream handle
valueP = Pointer to Boolean
valueLenP = Pointer to Int32 variable set to sizeof(Boolean)
RETURNS:
zero on success; fileErr... on error. The Boolean variable will be set to non-zero if the file was created.
fileOpGetOpenDbRef
Get the open database reference (handle) of the underlying database that implements the stream (NULL if none); this is needed for performing Palm OS-specific operations on the underlying database, such as changing or getting creator and type, version, backup/reset bits, and so on.
ARGUMENTS:
stream = open stream handle
valueP = Pointer to DmOpenRef variable
valueLenP = Pointer to Int32 variable set to sizeof(DmOpenRef)
RETURNS:
zero on success; fileErr... on error. The DmOpenRef variable will be set to the file's open db reference that may be passed to Data Manager calls;
WARNING: Do not make any changes to the data of the underlying database -- doing so will corrupt the file stream.
fileOpFlush
Flush any cached data to storage.
ARGUMENTS:
stream = open stream handle
valueP = NULL
valueLenP = NULL
RETURNS:
zero on success; fileErr... on error;

Compatibility

Implemented only if 3.0 New Feature Set is present.

See Also

FileClearerr(), FileEOF(), FileError(), FileFlush(), FileGetLastError(), FileRewind()

FileDelete Function ^TOP^

Purpose

Deletes the specified file stream from the specified card. Only a closed stream may be passed to this function.

Declared In

FileStream.h

Prototype

Err FileDelete (
   UInt16cardNo,
   constChar*nameP
)

Parameters

cardNo
Card on which the file stream to delete resides. Currently, no Palm OS® devices support multiple cards, so this value must be 0.
nameP
String that is the name of the stream to delete.

Returns

0 if no error, or a fileErr code if an error occurs. See the section "File Streaming Error Codes" for more information.

Compatibility

Implemented only if 3.0 New Feature Set is present.

See Also

FileOpen()

FileDmRead Macro ^TOP^

Purpose

Reads data from a file stream into a chunk, record, or resource residing in a database.

Declared In

FileStream.h

Prototype

#define FileDmRead(
   stream,
   startOfDmChunkP,
   destOffset,
   objSize,
   numObj,
   errP
)

Parameters

stream
Handle to open stream.
startOfDmChunkP
Pointer to beginning of chunk, record or resource residing in a database.
destOffset
Offset from startOfDmChunkP (base pointer) to the destination area (must be >= 0).
objSize
Size of each stream object to read.
numObj
Number of stream objects to read.
errP
Pointer to variable that is to hold the error code returned by this function. Pass NULL to ignore. See the section "File Streaming Error Codes" for more information.

Returns

The number of whole objects that were read—note that the number of objects actually read may be less than the number requested.

Comments

When the number of objects actually read is less than the number requested, you may be able to determine the cause of this result by examining the return value of the errP parameter or by calling the FileGetLastError() function. If the cause is insufficient data in the stream to satisfy the full request, the current stream position is at end-of-file and the "end of file" indicator is set. If a non-NULL pointer was passed as the value of the errP parameter when the FileDmRead function was called and an error was encountered, *errP holds a non-zero error code when the function returns. In addition, the FileError() and FileEOF() functions may be used to check for I/O errors.

Compatibility

Implemented only if 3.0 New Feature Set is present.

See Also

FileRead(), FileError(), FileEOF()

FileEOF Function ^TOP^

Purpose

Get end-of-file status (err = fileErrEOF indicates end of file condition).

Declared In

FileStream.h

Prototype

Err FileEOF (
   FileHandstream
) 

Parameters

stream
Handle to open stream.

Returns

0 if not end of file; non-zero if end of file. See the section "File Streaming Error Codes" for more information.

Comments

This function's behavior is similar to that of the feof function provided by the C programming language runtime library.

Use FileClearerr() to clear the I/O error status.

Compatibility

Implemented only if 3.0 New Feature Set is present.

See Also

FileClearerr(), FileGetLastError(), FileRewind()

FileError Function ^TOP^

Purpose

Get I/O error status.

Declared In

FileStream.h

Prototype

Err FileError (
   FileHandstream
) 

Parameters

stream
Handle to open stream.

Returns

0 if no error, and non-zero if an I/O error indicator has been set for this stream. See the section "File Streaming Error Codes" for more information.

Comments

This function's behavior is similar to that of the C programming language's ferror runtime function.

Use FileClearerr() to clear the I/O error status.

Compatibility

Implemented only if 3.0 New Feature Set is present.

See Also

FileClearerr(), FileGetLastError(), FileRewind()

FileFlush Function ^TOP^

Purpose

Flush cached data to storage.

Declared In

FileStream.h

Prototype

Err FileFlush (
   FileHandstream
) 

Parameters

stream
Handle to open stream.

Returns

0 if no error, or a fileErr code if an error occurs. See the section "File Streaming Error Codes" for more information.

Comments

It is not always necessary to call this function explicitly—certain operations flush the contents of a stream automatically; for example, streams are flushed when they are closed. Because this function's behavior is similar to that of the fflush function provided by the C programming language runtime library, you only need to call it explicitly under circumstances similar to those in which you would call fflush explicitly.

Compatibility

Implemented only if 3.0 New Feature Set is present.

FileGetLastError Function ^TOP^

Purpose

Get error code from last operation on file stream, and clear the last error code value (will not change end of file or I/O error status -- use FileClearerr() to reset all error codes)

Declared In

FileStream.h

Prototype

Err FileGetLastError (
   FileHandstream
) 

Parameters

stream
Handle to open stream.

Returns

Error code returned by the last file stream operation. See the section "File Streaming Error Codes" for more information.

Compatibility

Implemented only if 3.0 New Feature Set is present.

See Also

FileClearerr(), FileEOF(), FileError()

FileOpen Function ^TOP^

Purpose

Open existing file stream or create an open file stream for I/O in the mode specified by the openMode parameter.

Declared In

FileStream.h

Prototype

FileHand FileOpen (
   UInt16cardNo,
   constChar*nameP,
   UInt32type,
   UInt32creator,
   UInt32openMode,
   Err*errP
)

Parameters

cardNo
Card on which the file stream to open resides. Currently, no Palm Powered devices support multiple cards, so this value must be 0.
nameP
Pointer to text string that is the name of the file stream to open or create. This value must be a valid name—no wildcards allowed, must not be NULL.
type
File type of stream to open or create. Pass 0 for wildcard, in which case sysFileTFileStream is used if the stream needs to be created and fileModeTemporary is not specified. If type is 0 and fileModeTemporary is specified, then sysFileTTemp is used for the file type of the stream this function creates.
creator
Creator of stream to open or create. Pass 0 for wildcard, in which case the current application's creator ID is used for the creator of the stream this function creates.
openMode
Mode in which to open the file stream. You must specify only one primary mode selector. Additionally, you can use the | operator (bitwise inclusive OR) to append one or more secondary mode selectors to the primary mode selector. See "Primary Open Mode Constants" and "Secondary Open Mode Constants" for the list of possible values.
errP
Pointer to variable that is to hold the error code returned by this function. Pass NULL to ignore. See the section "File Streaming Error Codes" for a list of error codes.

Returns

If successful, returns a handle to an open file stream; otherwise, returns 0.

In some cases, on some platforms, FileOpen() returns a non-zero value when it has failed to open a file; thus, it is always a good idea to check the errP parameter value to determine if an error has occurred.

Comments

The fileModeReadOnly, fileModeReadWrite, fileModeUpdate, and fileModeAppend modes are mutually exclusive—pass only one of them to the FileOpen function!

When the fileModeTemporary open mode is used and the file type passed to FileOpen is 0, the FileOpen function uses sysFileTTemp (defined in SystemMgr.rh) for the file type, as recommended. In future versions of Palm OS, this configuration will enable the automatic cleanup of undeleted temporary files after a system crash. Automatic post-crash cleanup is not implemented in current versions of Palm OS.

To open a file stream even if it has a different type and creator than specified, pass the fileModeAnyTypeCreator selector as a flag in the openMode parameter to the FileOpen() function.

The fileModeLeaveOpen mode is an esoteric option that most applications should not use. It may be useful for a library that needs to open a stream from the current application's context and keep it open even after the current application quits. By default, Palm OS automatically closes all databases that were opened in a particular application's context when that application quits. The fileModeLeaveOpen option overrides this default behavior.

Compatibility

Implemented only if 3.0 New Feature Set is present.

FileRead Macro ^TOP^

Purpose

Reads data from a stream into a buffer. Do not use this macro to read data into a chunk, record or resource residing in a database—you must use the FileDmRead() macro for such operations.

Declared In

FileStream.h

Prototype

#define FileRead(
   stream,
   bufP,
   objSize,
   numObj,
   errP
)

Parameters

stream
Handle to open stream.
bufP
Pointer to beginning of buffer into which data is read
objSize
Size of each stream object to read.
numObj
Number of stream objects to read.
errP
Pointer to variable that is to hold the error code returned by this function. Pass NULL to ignore. See the section "File Streaming Error Codes" for a list of error codes.

Returns

The number of whole objects that were read—note that the number of objects actually read may be less than the number requested.

Comments

Do not use this macro to read data into a chunk, record or resource residing in a database—you must use the FileDmRead() macro for such operations.

When the number of objects actually read is fewer than the number requested, you may be able to determine the cause of this result by examining the return value of the errP parameter or by calling the FileGetLastError() function. If the cause is insufficient data in the stream to satisfy the full request, the current stream position is at end-of-file and the "end of file" indicator is set. If a non-NULL pointer was passed as the value of the errP parameter when the FileRead function was called and an error was encountered, *errP holds a non-zero error code when the function returns. In addition, the FileError() and FileEOF() functions may be used to check for I/O errors.

Compatibility

Implemented only if 3.0 New Feature Set is present.

See Also

FileDmRead()

FileRewind Function ^TOP^

Purpose

Reset position marker to beginning of stream and clear all error codes.

Declared In

FileStream.h

Prototype

Err FileRewind (
   FileHandstream
) 

Parameters

stream
Handle to open stream.

Returns

0 if no error, or a fileErr code if an error occurs. See the section "File Streaming Error Codes" for more information.

Compatibility

Implemented only if 3.0 New Feature Set is present.

See Also

FileSeek(), FileTell(), FileClearerr(), FileEOF(), FileError(), FileGetLastError()

FileSeek Function ^TOP^

Purpose

Set current position within a file stream, extending the stream as necessary if it was opened with write access.

Declared In

FileStream.h

Prototype

Err FileSeek (
   FileHandstream,
   Int32offset,
   FileOriginEnumorigin
) 

Parameters

stream
Handle to open stream.
offset
Position to set, expressed as the number of bytes from origin. This value may be positive, negative, or 0.
origin
Describes the origin of the position change. Possible values are:
fileOriginBeginning
From the beginning (first data byte of file).
fileOriginCurrent
From the current position.
fileOriginEnd
From the end of file (one position beyond last data byte).

Returns

0 if no error, or a fileErr code if an error occurs. See the section "File Streaming Error Codes" for more information.

Comments

Attempting to seek beyond end-of-file in a read-only stream results in an I/O error.

This function's behavior is similar to that of the fseek function provided by the C programming language runtime library.

Compatibility

Implemented only if 3.0 New Feature Set is present.

See Also

FileRewind(), FileTell()

FileTell Function ^TOP^

Purpose

Retrieves the current position and, optionally, file size, of a stream.

Declared In

FileStream.h

Prototype

Int32 FileTell (
   FileHandstream,
   Int32*fileSizeP,
   Err*errP
) 

Parameters

stream
Handle to open stream.
fileSizeP
Pointer to variable that holds value describing size of stream in bytes when this function returns. Pass NULL to ignore.
errP
Pointer to variable that is to hold the error code returned by this function. Pass NULL to ignore. See the section "File Streaming Error Codes" for a list of possible error codes.

Returns

If successful, returns current position, expressed as an offset in bytes from the beginning of the stream. If an error was encountered, returns -1 as a signed long integer.

Comments

The FileTell function can return the size of the input stream; as such, it provides some of the functionality of the standard C library stat function. Note, however, that unlike the stat function, FileTell requires that the file be open.

Compatibility

Implemented only if 3.0 New Feature Set is present.

See Also

FileRewind(), FileSeek()

FileTruncate Function ^TOP^

Purpose

Truncate the file stream to a specified size; not allowed on streams open in destructive read mode or read-only mode.

Declared In

FileStream.h

Prototype

Err FileTruncate (
   FileHandstream,
   Int32newSize
) 

Parameters

stream
Handle of open stream.
newSize
New size; must not exceed current stream size.

Returns

0 if no error, or a fileErr code if an error occurs. See the section "File Streaming Error Codes" for a list of possible error codes.

Compatibility

Implemented only if 3.0 New Feature Set is present.

See Also

FileTell()

FileWrite Function ^TOP^

Purpose

Write data to a stream.

Declared In

FileStream.h

Prototype

Int32 FileWrite (
   FileHandstream,
   constvoid*dataP,
   Int32objSize,
   Int32numObj,
   Err*errP
) 

Parameters

stream
Handle to open stream.
dataP
Pointer to buffer holding data to write.
objSize
Size of each stream object to write; must be 0.
numObj
Number of stream objects to write.
errP
Optional pointer to variable that holds the error code returned by this function. Pass NULL to ignore. See the section "File Streaming Error Codes" for a list of possible error codes.

Returns

The number of whole objects that were written—note that the number of objects actually written may be less than the number requested. Should available storage be insufficient to satisfy the entire request, as much of the requested data as possible is written to the stream, which may result in the last object in the stream being incomplete.

Comments

Writing to files opened without write access or those that are in destructive read state is not allowed; thus, you cannot call the FileWrite(), FileSeek(), or FileTruncate() functions on a stream that is in destructive read mode. One exception to this rule applies to streams that were opened in "write + append" mode and then switched into destructive read state. In this case, the FileWrite function can append data to the stream, but it also preserves the current stream position so that subsequent reads pick up where they left off (you can think of this as a pseudo-pipe).

Compatibility

Implemented only if 3.0 New Feature Set is present.

File Streaming Error Codes ^TOP^

This section lists all error codes returned by the file streaming functions.

Error Code

Value

Meaning

fileErrMemErr

(fileErrorClass|1)

Out of memory error

fileErrInvalidParam

(fileErrorClass|2)

Invalid parameter value passed

fileErrCorruptFile

(fileErrorClass|3)

Alleged stream is corrupted, invalid, or not a stream

fileErrNotFound

(fileErrorClass|4)

Couldn't find the stream

fileErrTypeCreatorMismatch

(fileErrorClass|5)

Type and/or creator not what was specified

fileErrReplaceError

(fileErrorClass|6)

Couldn't replace existing stream

fileErrCreateError

(fileErrorClass|7)

Couldn't create new stream

fileErrOpenError

(fileErrorClass|8)

Generic open error

fileErrInUse

(fileErrorClass|9)

Stream couldn't be opened or deleted because it is in use

fileErrReadOnly

(fileErrorClass|10)

Couldn't open in write mode because existing stream is read-only

fileErrInvalidDescriptor

(fileErrorClass|11)

Invalid file descriptor (FileHandle)

fileErrCloseError

(fileErrorClass|12)

Error closing the stream

fileErrOutOfBounds

(fileErrorClass|13)

Attempted operation went out of bounds of the stream

fileErrPermissionDenied

(fileErrorClass|14)

Couldn't write to a stream open for read-only access

fileErrIOError

(fileErrorClass|15)

Generic I/O error

fileErrEOF

(fileErrorClass|16)

End-of-File error

fileErrNotStream

(fileErrorClass|17)

Attempted to open an entity that is not a stream