std::basic_ifstream<CharT,Traits>::basic_ifstream

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms 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 in C++98)

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 in C++98)

ostrstream (deprecated in C++98)

strstream (deprecated in C++98)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

 

std::basic_ifstream

Member functions

basic_ifstream::basic_ifstream

basic_ifstream::operator= (C++11)

basic_ifstream::swap (C++11)

basic_ifstream::rdbuf

File operations

basic_ifstream::is_open

basic_ifstream::open

basic_ifstream::close

Non-member functions

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

 

basic_ifstream();	(1)
explicit basic_ifstream( const char* filename,                 std::ios_base::openmode mode = ios_base::in );	(2)
explicit basic_ifstream( const std::filesystem::path::value_type* filename,                 std::ios_base::openmode mode = ios_base::in );	(3)	(since C++17)
explicit basic_ifstream( const std::string& filename,                 std::ios_base::openmode mode = ios_base::in );	(4)	(since C++11)
explicit basic_ifstream( const std::filesystem::path& filename,                 std::ios_base::openmode mode = ios_base::in );	(5)	(since C++17)
basic_ifstream( basic_ifstream&& other );	(6)	(since C++11)
basic_ifstream( const basic_ifstream& 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 | std::ios_base::in) (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_ifstream(filename.c_str(), mode).

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. It is bitmask type, the following constants are defined: 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
other	-	another file stream to use as source

Example

Run this code

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

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_istream<CharT,Traits>)