fstream(C++)

Syntax

#include <fstream.h>

typedef long streamoff, streampos;
class ios {
public:
	enum	seek_dir { beg, cur, end };
	enum	open_mode { in, out, ate, app, trunc, nocreate, noreplace };
	enum	io_state { goodbit=0, eofbit, failbit, badbit };
	// and lots of other stuff, see ios(C++) ...
} ;

class ifstream : istream {
		ifstream() ;
		~ifstream() ;
		ifstream(const char* name, int =ios::in,
			        	int prot =filebuf::openprot) ;
		ifstream(int fd) ;
		ifstream(int fd, char* p, int l) ;

	void	attach(int fd) ;
	int	detach() ;
	void	close() ;
	void	open(char* name, int =ios::in,
			int prot=filebuf::openprot) ;
	filebuf*	rdbuf() ;
	void	setbuf(char* p, int l) ;
};

class ofstream : ostream {
		ofstream() ;
		~ofstream() ;
		ofstream(const char* name, int =ios::out,
			        	int prot =filebuf::openprot) ;
		ofstream(int fd) ;
		ofstream(int fd, char* p, int l) ;

	void	attach(int fd) ;
	int	detach() ;
	void	close() ;
	void	open(char* name, int =ios::out,
					int prot=filebuf::openprot) ;
	filebuf*	rdbuf() ;
	void	setbuf(char* p, int l) ;
};

class fstream : iostream {
		fstream() ;
		~fstream() ;
		fstream(const char* name, int mode,
			        	int prot =filebuf::openprot) ;
		fstream(int fd) ;
		fstream(int fd, char* p, int l) ;

	void	attach(int fd) ;
	int	detach();
	void	close() ;
	void	open(char* name, int mode, int prot=filebuf::openprot) ;
	filebuf*	rdbuf() ;
	void	setbuf(char* p, int l) ;
};

Description

In the following descriptions, assume

• f is any of ifstream, ofstream, or fstream

• pfb is a filebuf*

• psb is a streambuf*

• name and ptr are char*s

• i, fd, len, and prot are ints

• mode is an int representing an open_mode

Constructors

xstream()

Constructs an unopened xstream.

xstream(name, mode, prot)

Constructs an xstream and opens file name using mode as the open mode and prot as the protection mode. By default, prot is filebuf::openprot, which is 0644. The error state (io_state) of the constructed xstream will indicate failure in case the open fails.

xstream(d)

Constructs an xstream connected to file descriptor d, which must be already open.

xstream(d,ptr,len)

Constructs an xstream connected to file descriptor d, and, in addition, initializes the associated filebuf to use the len bytes at ptr as the reserve area. If ptr is null or len is 0, the filebuf will be unbuffered.

Member functions

f.attach(d)

Connects f to the file descriptor d. A failure occurs when f is already connected to a file. A failure sets ios::failbit in f's error state.

d=f.detach()

Disconnects the attached file descriptor from f and returns the file descriptor. Before disconnection, flushes any waiting output to the file associated with the file descriptor.

f.close()

Closes any associated filebuf and thereby breaks the connection of the f to a file. f's error state is cleared except on failure. A failure occurs when the call to f.rdbuf()->close() fails.

f.open(name,mode,prot)

Opens file name and connects f to it. If the file does not already exist, an attempt is made to create it with protection mode prot unless ios::nocreate is set. By default, prot is filebuf::openprot, which is 0644. Failure occurs if f is already open, or the call to f.rdbuf()->open() fails. ios::failbit is set in f's error status on failure. The members of open_mode are bits that may be or'ed together. (Because the or'ing returns an int, open() takes an int rather than an open_mode argument.) The meanings of these bits in mode are:

ios::app

A seek to the end of file is performed. Subsequent data written to the file is always added (appended) at the end of file. On some systems this is implemented in the operating system. In others it is implemented by seeking to the end of the file before each write. ios::app implies ios::out.

ios::ate

A seek to the end of the file is performed during the open(). ios::ate does not imply ios::out.

ios::in

The file is opened for input. ios::in is implied by construction and opens of ifstreams. For fstreams it indicates that input operations should be allowed if possible. It is legal to include ios::in in the modes of an ostream in which case it implies that the original file (if it exists) should not be truncated. If the file being opened for input does not exist, the open will fail.

ios::out

The file is opened for output. ios::out is implied by construction and opens of ofstreams. For fstream it says that output operations are to be allowed. ios::out may be specified even if prot does not permit output.

ios::trunc

If the file already exists, its contents will be truncated (discarded). This mode is implied when ios::out is specified (including implicit specification for ofstream) and neither ios::ate nor ios::app is specified.

ios::nocreate

If the file does not already exist, the open() will fail.

ios::noreplace

If the file already exists, the open() will fail. Only valid with ios::out.

pfb=f.rdbuf()

Returns a pointer to the filebuf associated with f. fstream::rdbuf() has the same meaning as iostream::rdbuf() but is typed differently.

f.setbuf(p,len)

Has the usual effect of a setbuf() (see filebuf(C++)), offering space for a reserve area or requesting unbuffered I/O. Normally the returned psb is f.rdbuf(), but it is 0 on failure. A failure occurs if f is open or the call to f.rdbuf()->setbuf fails.

See also