basic_filebuf

Overview

basic_filebuf is a template based class used for read from or/and write to files in the file system.

Details

ifstream, ofstream and fstream classes uses a basic_filebuf to read from or/and write to files. It's derived from basic_streambuf class.

Syntax

template<class CharT, class Traits = char_traits<CharT>> 
class basic_filebuf:public basic_streambuf<CharT,Traits> 

where CharT can be char or wchar_t.

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. These are used in calls such as fopen(). These are bitmask type flags that can be ORed. The following describes different values.

Name	Description
in	Open file for reading.
out	Open file for writing.
ate	Set the stream's position indicator to the end of the stream on opening.
app	Set the stream's position indicator to the end of the stream before each output operation.
trunc	Any current content is discarded, assuming a length of zero on opening.
binary	Consider stream as binary rather than text.

Note it's possible to have multiple flags set. i.e., in | out set at the same time.
Note that in case of ate, writes can be on done anywhere in the stream. For example, begin or middle. In case of app, writes can be done only in the end.
Note that difference between text and binary files is that in a text file individual lines are demarcated by a newline character \n or \r\n. In case of binary files there are no such demarcation.

Methods

These are the public functions available for the clients like ifstream, ofstream and fstream classes.

Name
Description
bool is_open()
Checks if the file stream has an associated file.
Returns true if it's open. Otherwise, false.
basic_filebuf* open
(const char* filename, 
ios_base::openmode mode)
basic_filebuf* open
(const string& filename, 
ios_base::openmode mode)
Opens and associates the file with name filename with the file stream.
If the call fails, returns nullptr, otherwise returns this.
Calls the first version with open(filename.c_str(),mode)
The mode constants are defined in ios_base class. 
If the mode has both ios_base::trunc and ios_base::app set, the opening operation fails. It also fails if ios_base::trunc is set but ios_base::out is not.
void close()
Closes the file currently associated with the object, disassociating it from the stream.
Any pending output sequence is written to the file.
Example
filebuf file;
    
file.open("/usr/share/dict/words",ios_base::in);
bool bsuccess = file.is_open();
file.close();

file.open("test.txt",ios_base::out);
bsuccess = file.is_open();
file.close();