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Describes an object that controls extraction of elements and encoded objects from a stream buffer of class basic_filebuf<Elem, Tr> , with elements of type Elem , whose character traits are determined by the class Tr .

For more information, see basic_filebuf .

Syntax

template <class Elem, class Tr = char_traits<Elem>>
class basic_ifstream : public basic_istream<Elem, Tr>
Parameters
The basic element of the file buffer.

The traits of the basic element of the file buffer (usually char_traits<Elem>).

Remarks
The object stores an object of class basic_filebuf<Elem, Tr>.
Example
The following example shows how to read in text from a file.
// basic_ifstream_class.cpp
// compile with: /EHsc
#include <fstream>
#include <iostream>
using namespace std;
int main(int argc, char **argv)
    ifstream ifs("basic_ifstream_class.txt");
    if (!ifs.bad())
        // Dump the contents of the file to cout.
        cout << ifs.rdbuf();
        ifs.close();
Input: basic_ifstream_class.txt
This is the contents of basic_ifstream_class.txt.
Output
This is the contents of basic_ifstream_class.txt.
Constructors
Constructor
Description
Namespace: std
 basic_ifstream::basic_ifstream
Constructs an object of type basic_ifstream.
basic_ifstream();
explicit basic_ifstream(
    const char* _Filename,
    ios_base::openmode _Mode = ios_base::in,
    int _Prot = (int)ios_base::_Openprot);
explicit basic_ifstream(
    const wchar_t* _Filename,
    ios_base::openmode _Mode = ios_base::in,
    int _Prot = (int)ios_base::_Openprot);
basic_ifstream(basic_ifstream&& right);
Parameters
_Filename

The name of the file to open.
_Mode

One of the enumerations in ios_base::openmode.
_Prot

The default file opening protection, equivalent to the shflag parameter in _fsopen, _wfsopen.
Remarks
The first constructor initializes the base class by calling basic_istream(sb), where sb is the stored object of class basic_filebuf<Elem, Tr>. It also initializes sb by calling basic_filebuf<Elem, Tr>.
The second and third constructors initialize the base class by calling basic_istream(sb). It also initializes sb by calling basic_filebuf<Elem, Tr>, then sb.open(_Filename, _Mode | ios_base::in). If the latter function returns a null pointer, the constructor calls setstate(failbit).
The fourth constructor initializes the object with the contents of right, treated as an rvalue reference.
For more information, see basic_istream, basic_filebuf, setstate, and open.
Example
The following example shows how to read in text from a file. To create the file, see the example for basic_ofstream::basic_ofstream.
// basic_ifstream_ctor.cpp
// compile with: /EHsc
#include <fstream>
#include <iostream>
using namespace std;
int main(int argc, char **argv)
    ifstream ifs("basic_ifstream_ctor.txt");
    if (!ifs.bad())
        // Dump the contents of the file to cout.
        cout << ifs.rdbuf();
        ifs.close();
 basic_ifstream::close
Closes a file.
void close();
Remarks
The member function calls rdbuf -> close.
Example
See basic_filebuf::close for an example that uses close.
 basic_ifstream::is_open
Determines if a file is open.
bool is_open() const;
Return Value
true if the file is open, false otherwise.
Remarks
The member function returns rdbuf -> is_open.
Example
See basic_filebuf::is_open for an example that uses is_open.
 basic_ifstream::open
Opens a file.
void open(
    const char* _Filename,
    ios_base::openmode _Mode = ios_base::in,
    int _Prot = (int)ios_base::_Openprot);
void open(
    const char* _Filename,
    ios_base::openmode _Mode);
void open(
    const wchar_t* _Filename,
    ios_base::openmode _Mode = ios_base::in,
    int _Prot = (int)ios_base::_Openprot);
void open(
    const wchar_t* _Filename,
    ios_base::openmode _Mode);
Parameters
_Filename

The name of the file to open.
_Mode

One of the enumerations in ios_base::openmode.
_Prot

The default file opening protection, equivalent to the shflag parameter in _fsopen, _wfsopen.
Remarks
The member function calls rdbuf->open(_Filename, _Mode | ios_base::in). For more information, see rdbuf and basic_filebuf::open. If open fails, the function calls setstate(failbit), which may throw an ios_base::failure exception. For more information, see setstate.
Example
See basic_filebuf::open for an example that uses open.
 basic_ifstream::operator=
Assigns the content of this stream object. This is a move assignment involving an rvalue that doesn't leave a copy behind.
basic_ifstream& operator=(basic_ifstream&& right);
Parameters
right

An rvalue reference to a basic_ifstream object.
Return Value
Returns *this.
Remarks
The member operator replaces the contents of the object by using the contents of right, treated as an rvalue reference. For more information, see Lvalues and Rvalues.
 basic_ifstream::rdbuf
Returns the address of the stored stream buffer.
basic_filebuf<Elem, Tr> *rdbuf() const
Return Value
A pointer to a basic_filebuf object representing the stored stream buffer.
Example
See basic_filebuf::close for an example that uses rdbuf.
 basic_ifstream::swap
Exchanges the contents of two basic_ifstream objects.
void swap(basic_ifstream& right);
Parameters
right

A reference to another stream buffer.
Remarks
The member function exchanges the contents of this object for the contents of right.
See also
Thread Safety in the C++ Standard Library

iostream Programming

iostreams Conventions