wxFile Class Reference

#include <wx/file.h>

Detailed Description

A wxFile performs raw file I/O.

This is a very small class designed to minimize the overhead of using it - in fact, there is hardly any overhead at all, but using it brings you automatic error checking and hides differences between platforms and compilers. wxFile also automatically closes the file in its destructor so you won't forget to do so. wxFile is a wrapper around file descriptor. - see also wxFFile for a wrapper around FILE structure.

wxFileOffset is used by the wxFile functions which require offsets as parameter or return them. If the platform supports it, wxFileOffset is a typedef for a native 64 bit integer, otherwise a 32 bit integer is used for wxFileOffset.

Library:  wxBase

Category:  File Handling

Public Types
enum	OpenMode {   read,   write,   read_write,   write_append,   write_excl }
	The OpenMode enumeration defines the different modes for opening a file with wxFile. More...
enum	{   fd_invalid = -1,   fd_stdin,   fd_stdout,   fd_stderr }
	Standard file descriptors. More...

Public Member Functions
	wxFile ()
	Default constructor. More...
	wxFile (const wxString &filename, wxFile::OpenMode mode=wxFile::read)
	Opens a file with a filename. More...
	wxFile (int fd)
	Associates the file with the given file descriptor, which has already been opened. More...
	~wxFile ()
	Destructor will close the file. More...
int	GetLastError () const
	Returns the error code for the last unsuccessful operation. More...
void	ClearLastError ()
	Resets the error code. More...
void	Attach (int fd)
	Attaches an existing file descriptor to the wxFile object. More...
bool	Close ()
	Closes the file. More...
bool	Create (const wxString &filename, bool overwrite=false, int access=wxS_DEFAULT)
	Creates a file for writing. More...
int	Detach ()
	Get back a file descriptor from wxFile object - the caller is responsible for closing the file if this descriptor is opened. More...
bool	Eof () const
	Returns true if the end of the file has been reached. More...
bool	Flush ()
	Flushes the file descriptor. More...
wxFileKind	GetKind () const
	Returns the type of the file. More...
bool	IsOpened () const
	Returns true if the file has been opened. More...
wxFileOffset	Length () const
	Returns the length of the file. More...
bool	Open (const wxString &filename, wxFile::OpenMode mode=wxFile::read, int access=wxS_DEFAULT)
	Opens the file, returning true if successful. More...
ssize_t	Read (void *buffer, size_t count)
	Reads from the file into a memory buffer. More...
bool	ReadAll (wxString *str, const wxMBConv &conv=wxConvAuto())
	Reads the entire contents of the file into a string. More...
wxFileOffset	Seek (wxFileOffset ofs, wxSeekMode mode=wxFromStart)
	Seeks to the specified position. More...
wxFileOffset	SeekEnd (wxFileOffset ofs=0)
	Moves the file pointer to the specified number of bytes relative to the end of the file. More...
wxFileOffset	Tell () const
	Returns the current position or wxInvalidOffset if file is not opened or if another error occurred. More...
size_t	Write (const void *buffer, size_t count)
	Write data to the file (descriptor). More...
bool	Write (const wxString &s, const wxMBConv &conv=wxConvUTF8)
	Writes the contents of the string to the file, returns true on success. More...
int	fd () const
	Returns the file descriptor associated with the file. More...

Static Public Member Functions
static bool	Access (const wxString &name, wxFile::OpenMode mode)
	This function verifies if we may access the given file in specified mode. More...
static bool	Exists (const wxString &filename)
	Returns true if the given name specifies an existing regular file (not a directory or a link). More...

Member Enumeration Documentation

anonymous enum

Standard file descriptors.

Enumerator
fd_invalid
fd_stdin
fd_stdout
fd_stderr

enum wxFile::OpenMode

The OpenMode enumeration defines the different modes for opening a file with wxFile.

It is also used with wxFile::Access function.

Enumerator
read	Open file for reading or test if it can be opened for reading with Access()
write	Open file for writing deleting the contents of the file if it already exists or test if it can be opened for writing with Access().
read_write	Open file for reading and writing; cannot be used with Access()
write_append	Open file for appending: the file is opened for writing, but the old contents of the file are not erased and the file pointer is initially placed at the end of the file; cannot be used with Access(). This is the same as OpenMode::write if the file doesn't exist.
write_excl	Open the file securely for writing (Uses O_EXCL | O_CREAT). Will fail if the file already exists, else create and open it atomically. Useful for opening temporary files without being vulnerable to race exploits.

Constructor & Destructor Documentation

wxFile::wxFile

(

)

Default constructor.

wxFile::wxFile	(	const wxString &	filename,
		wxFile::OpenMode	mode = wxFile::read
	)

Opens a file with a filename.

Parameters

filename	The filename.
mode	The mode in which to open the file.

Warning

You should use IsOpened() to verify that the constructor succeeded.

wxFile::wxFile

(

int

fd

)

Associates the file with the given file descriptor, which has already been opened.

See Attach() for the list of predefined descriptors.

Parameters

fd	An existing file descriptor.

wxFile::~wxFile

(

)

Destructor will close the file.

Note

This destructor is not virtual so you should not use wxFile polymorphically.

Member Function Documentation

static bool wxFile::Access ( const wxString &  name, wxFile::OpenMode  mode  )

static

This function verifies if we may access the given file in specified mode.

Only values of wxFile::read or wxFile::write really make sense here.

void wxFile::Attach

(

int

fd

)

Attaches an existing file descriptor to the wxFile object.

Examples of predefined file descriptors are 0, 1 and 2 which correspond to stdin, stdout and stderr (and have symbolic names of wxFile::fd_stdin, wxFile::fd_stdout and wxFile::fd_stderr).

The descriptor should be already opened and it will be closed by wxFile object.

void wxFile::ClearLastError

(

)

Resets the error code.

GetLastError() will return 0 until the next error occurs.

Since

2.9.2

bool wxFile::Close

(

)

Closes the file.

bool wxFile::Create	(	const wxString &	filename,
		bool	overwrite = false,
		int	access = wxS_DEFAULT
	)

Creates a file for writing.

If the file already exists, setting overwrite to true will ensure it is overwritten.

access may be an OR combination of the wxPosixPermissions enumeration values.

int wxFile::Detach

(

)

Get back a file descriptor from wxFile object - the caller is responsible for closing the file if this descriptor is opened.

IsOpened() will return false after call to Detach().

Returns

The file descriptor (this is new since wxWidgets 3.0.0, in the previous versions this method didn't return anything).

bool wxFile::Eof

(

)

const

Returns true if the end of the file has been reached.

Note that the behaviour of the file pointer-based class wxFFile is different as wxFFile::Eof() will return true here only if an attempt has been made to read past the last byte of the file, while wxFile::Eof() will return true even before such attempt is made if the file pointer is at the last position in the file.

Note also that this function doesn't work on unseekable file descriptors (examples include pipes, terminals and sockets under Unix) and an attempt to use it will result in an error message.

So, to read the entire file into memory, you should write a loop which uses Read() repeatedly and tests its return condition instead of using Eof() as this will not work for special files under Unix.

static bool wxFile::Exists ( const wxString &  filename )

static

Returns true if the given name specifies an existing regular file (not a directory or a link).

int wxFile::fd

(

)

const

Returns the file descriptor associated with the file.

bool wxFile::Flush

(

)

Flushes the file descriptor.

Note that Flush() is not implemented on some Windows compilers due to a missing fsync function, which reduces the usefulness of this function (it can still be called but it will do nothing on unsupported compilers).

wxFileKind wxFile::GetKind

(

)

const

Returns the type of the file.

int wxFile::GetLastError

(

)

const

Returns the error code for the last unsuccessful operation.

The error code is system-dependent and corresponds to the value of the standard errno variable when the last error occurred.

Notice that only simple accessors such as IsOpened() and Eof() (and this method itself) don't modify the last error value, all other methods can potentially change it if an error occurs, including the const ones such as Tell() or Length().

Since

2.9.2

See also

ClearLastError()

bool wxFile::IsOpened

(

)

const

Returns true if the file has been opened.

wxFileOffset wxFile::Length

(

)

const

Returns the length of the file.

bool wxFile::Open	(	const wxString &	filename,
		wxFile::OpenMode	mode = wxFile::read,
		int	access = wxS_DEFAULT
	)

Opens the file, returning true if successful.

Parameters

filename	The filename.
mode	The mode in which to open the file.
access	An OR-combination of wxPosixPermissions enumeration values.

ssize_t wxFile::Read	(	void *	buffer,
		size_t	count
	)

Reads from the file into a memory buffer.

Parameters

buffer	Buffer to write in
count	Bytes to read

Returns

The number of bytes read, or the symbol wxInvalidOffset.

bool wxFile::ReadAll	(	wxString *	str,
		const wxMBConv &	conv = wxConvAuto()
	)

Reads the entire contents of the file into a string.

Parameters

str	Non-NULL pointer to a string to read data into.
conv	Conversion object to use in Unicode build; by default supposes that file contents is encoded in UTF-8 but falls back to the current locale encoding (or Latin-1 if it is UTF-8 too) if it is not.

Returns

true if file was read successfully, false otherwise.

Since

2.9.5

wxFileOffset wxFile::Seek	(	wxFileOffset	ofs,
		wxSeekMode	mode = wxFromStart
	)

Seeks to the specified position.

Parameters

ofs	Offset to seek to.
mode	One of wxFromStart, wxFromEnd, wxFromCurrent.

Returns

The actual offset position achieved, or wxInvalidOffset on failure.

wxFileOffset wxFile::SeekEnd

(

wxFileOffset

ofs = 0

)

Moves the file pointer to the specified number of bytes relative to the end of the file.

For example, SeekEnd(-5) would position the pointer 5 bytes before the end.

Parameters

ofs	Number of bytes before the end of the file.

Returns

The actual offset position achieved, or wxInvalidOffset on failure.

wxFileOffset wxFile::Tell

(

)

const

Returns the current position or wxInvalidOffset if file is not opened or if another error occurred.

size_t wxFile::Write	(	const void *	buffer,
		size_t	count
	)

Write data to the file (descriptor).

Parameters

buffer	Buffer from which to read data
count	Number of bytes to write

Returns

The number of bytes written.

bool wxFile::Write	(	const wxString &	s,
		const wxMBConv &	conv = wxConvUTF8
	)

Writes the contents of the string to the file, returns true on success.

The second argument is only meaningful in Unicode build of wxWidgets when conv is used to convert s to a multibyte representation.

Note that this method only works with NUL-terminated strings, if you want to write data with embedded NULs to the file you should use the other Write() overload.