std::basic_filebuf::open

C++

Language

Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

Input/output library

I/O manipulators

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

strstreambuf (deprecated)

basic_syncbuf (C++20)

Streams

Abstractions

ios_base

basic_ios

basic_istream

basic_ostream

basic_iostream

File I/O

basic_ifstream

basic_ofstream

basic_fstream

String I/O

basic_istringstream

basic_ostringstream

basic_stringstream

Array I/O

istrstream (deprecated)

ostrstream (deprecated)

strstream (deprecated)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

std::basic_filebuf

Public member functions

basic_filebuf::basic_filebuf

basic_filebuf::~basic_filebuf

basic_filebuf::operator= (C++11)

basic_filebuf::swap (C++11)

basic_filebuf::is_open

basic_filebuf::open

basic_filebuf::close

Protected member functions

basic_filebuf::showmanyc

basic_filebuf::underflow

basic_filebuf::uflow

basic_filebuf::pbackfail

basic_filebuf::overflow

basic_filebuf::setbuf

basic_filebuf::seekoff

basic_filebuf::seekpos

basic_filebuf::sync

basic_filebuf::imbue

Non-member functions

swap(std::basic_filebuf) (C++11)

std::basic_filebuf<CharT, Traits>* open( const char* s, std::ios_base::openmode mode )	(1)
std::basic_filebuf<CharT, Traits>* open( const std::string& str, std::ios_base::openmode mode )	(2)	(since C++11)
std::basic_filebuf<CharT, Traits>* open( const std::filesystem::path& p, std::ios_base::openmode mode )	(3)	(since C++17)
std::basic_filebuf<CharT, Traits>* open( const std::filesystem::path::value_type* s, std::ios_base::openmode mode )	(4)	(since C++17)

Opens the file with the given name (s, p.c_str() (since C++17) or str.c_str(), depending on the overload).

Overload (4) is only provided if std::filesystem::path::value_type is not char.

(since C++17)

The file is opened as if by calling std::fopen(s, modestring), where modestring is determined as follows:

modestring	openmode & ~ate	Action if file already exists	Action if file does not exist
"r"	in	Read from start	Failure to open
"w"	out, out|trunc	Destroy contents	Create new
"a"	app, out|app	Append to file	Create new
"r+"	out|in	Read from start	Error
"w+"	out|in|trunc	Destroy contents	Create new
"a+"	out|in|app, in|app	Write to end	Create new
"rb"	binary|in	Read from start	Failure to open
"wb"	binary|out, binary|out|trunc	Destroy contents	Create new
"ab"	binary|app, binary|out|app	Write to end	Create new
"r+b"	binary|out|in	Read from start	Error
"w+b"	binary|out|in|trunc	Destroy contents	Create new
"a+b"	binary|out|in|app, binary|in|app	Write to end	Create new

If openmode is not one of the modes listed, the open() fails.

If the open operation succeeds and openmode & std::ios_base::ate != 0 (the ate bit is set), repositions the file position to the end of file, as if by calling std::fseek(file, 0, SEEK_END). If the repositioning fails, calls close() and returns a null pointer to indicate failure.

If the associated file was already open, returns a null pointer right away.

Parameters

s, str, p	-	the file name to open
openmode	-	the file opening mode, a binary OR of the std::ios_base modes

Return value

this on success, a null pointer on failure.

Notes

open() is typically called through the constructor or the open() member function of std::basic_fstream.

See also

is_open	checks if the associated file is open (public member function)
close	flushes the put area buffer and closes the associated file (public member function)