basic_fstream

Overview

basic_fstream class is designed to read from and write to streams such as  files.

Details

The class template basic_fstream provides support for high level input and output operations on file streams. The supported operations include formatted input and output (e.g. integer values or whitespace-separated characters and characters strings) and unformatted input and output(e.g. raw characters and character arrays). 

basic_fstream class is basically derived class of  basic_ifstream and basic_ofstream. It has no additional functionality other than constructor. 

Syntax

template<class CharT, class Traits = char_traits<CharT>> 
class basic_fstream: public basic_iostream<CharT,Traits>

where CharT can be char or wchar_t. It's derived from basic_ios class.

member types
Following properties are defined.

Name	Definition
char_type	char,wchar_t
traits_type	char_traits<char_type>
int_type	char_traits<char_type>::int_type
pos_type	char_traits<char_type>::pos_type
off_type	char_traits<char_type>::off_type

openmode➹

The openmode flags indicate how the streams such as disk files or memory streams can be opened for IO operations such as read, write or append.

Constructor

Name

Description

basic_fstream (const char* filename, ios_base::openmode mode = ios_base::in|ios_base::out) basic_ifstream (const string& filename, ios_base::openmode mode = ios_base::in|ios_base::out) basic_fstream( basic_fstream&& other)

Constructs a basic_fstream object, initially associated with the file identified by its first argument (filename), open with the mode specified by mode. Internally, its basic_istream base constructor is passed a pointer to a newly constructed basic_filebuf object.  Then, basic_filebuf::open(filename,mode)  is called. If the call fails, the stream's failbit flag is set. Calls the first version with basic_fstream(filename.c_str(),mode) move constructor The mode constants are defined in ios_base class.

Methods

Name
Description
basic_streambuf* rdbuf()
Returns pointer to the underlying raw file device object.

Example
ifstream file("/usr/share/dict/words");
auto sb = file.rdbuf();
bool is_open()
Checks if the file stream has an associated file.
Effectively calls rdbuf()->is_open().

Example
ifstream file("/usr/share/dict/words");
bool bsuccess = file.is_open();
void open
(const char* filename, 
ios_base::openmode mode = ios_base::in)
void  open
(const string& filename, 
ios_base::openmode mode = ios_base::in)
Opens and associates the file with name filename with the file stream.
Internally, calls rdbuf()->open(filename,mode).
If the call fails, the stream's failbit flag is set. If the stream is already associated with a file (i.e., it is already open), calling this function fails.
Calls the first version with open(filename.c_str(),mode)
The mode constants are defined in ios_base class.

Example
ifstream file;
file.open("/usr/share/dict/words");
void close()
Closes the file currently associated with the object, disassociating it from the stream.
Any pending output sequence is written to the file.
Effectively calls rdbuf()->close(). If an error occurs during operation, setstate(failbit) is called.

Example
ifstream file;
file.open("/usr/share/dict/words");
file.close();