std::basic_fstream<CharT,Traits>::basic_fstream

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Input/output library

I/O manipulators

Print functions (C++23)

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

basic_spanbuf (C++23)

strstreambuf (C++98/26*)

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

basic_ispanstream (C++23)

basic_ospanstream (C++23)

basic_spanstream (C++23)

istrstream (C++98/26*)

ostrstream (C++98/26*)

strstream (C++98/26*)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

 

std::basic_fstream

Member functions

basic_fstream::basic_fstream

basic_fstream::operator= (C++11)

basic_fstream::swap (C++11)

basic_fstream::rdbuf

basic_fstream::native_handle (C++26)

File operations

basic_fstream::is_open

basic_fstream::open

basic_fstream::close

Non-member functions

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

 

basic_fstream();	(1)
explicit basic_fstream( const char* filename,                         std::ios_base::openmode mode                             = std::ios_base::in | std::ios_base::out );	(2)
explicit basic_fstream( const std::filesystem::path::value_type* filename,                         std::ios_base::openmode mode                             = std::ios_base::in | std::ios_base::out );	(3)	(since C++17)
explicit basic_fstream( const std::string& filename,                         std::ios_base::openmode mode                             = std::ios_base::in | std::ios_base::out );	(4)	(since C++11)
template< class FsPath > explicit basic_fstream( const FsPath& filename,                         std::ios_base::openmode mode                             = std::ios_base::in | std::ios_base::out );	(5)	(since C++17)
basic_fstream( basic_fstream&& other );	(6)	(since C++11)
basic_fstream( const basic_fstream& rhs ) = delete;	(7)	(since C++11)

Constructs new file stream.

1) Default constructor: constructs a stream that is not associated with a file: default-constructs the std::basic_filebuf and constructs the base with the pointer to this default-constructed std::basic_filebuf member.

2,3) First, performs the same steps as the default constructor, then associates the stream with a file by calling rdbuf()->open(filename, mode) (see std::basic_filebuf::open for the details on the effects of that call). If the open() call returns a null pointer, sets setstate(failbit). Overload (3) is only provided if std::filesystem::path::value_type is not char.(since C++17)

4,5) Same as basic_fstream(filename.c_str(), mode). (5) participates in overload resolution only if FsPath is std::filesystem::path.(since C++17)

6) Move constructor. First, move-constructs the base class from other (which does not affect the rdbuf() pointer), then move-constructs the std::basic_filebuf member, then calls this->set_rdbuf() to install the new basic_filebuf as the rdbuf() pointer in the base class.

7) The copy-constructor is deleted: this class is not copyable.

Parameters

filename	-	the name of the file to be opened
mode	-	specifies stream open mode. Following constants and bit-wise OR between them may be used: Constant Explanation app seek to the end of stream before each write binary open in binary mode in open for reading out open for writing trunc discard the contents of the stream when opening ate seek to the end of stream immediately after open noreplace (C++23) open in exclusive mode
other	-	another file stream to use as source

Example

Run this code

#include <fstream>
#include <string>
#include <utility>
 
int main()
{
    std::fstream f0;
    std::fstream f1("test.bin", std::ios::binary);
    std::string name = "example.txt";
    std::fstream f2(name);
    std::fstream f3(std::move(f1));
}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 460	C++98	the default argument of mode in overload (2) was missing (it is present in the synopsis)	added
LWG 3430	C++17	std::filesystem::path overload led to unwanted conversions	avoided by making it a template

See also

open	opens a file and associates it with the stream (public member function)
open	opens a file and configures it as the associated character sequence (public member function of std::basic_filebuf<CharT,Traits>)
set_rdbuf	replaces the rdbuf without clearing its error state (protected member function)
(constructor)	constructs the object (public member function of std::basic_iostream<CharT,Traits>)