c++11 standard template (STL) (std::basic_ifstream) (2)

defined in the header file <fstream>

template<     class CharT,     class Traits = std::char_traits<CharT> > class basic_ifstream : public std::basic_istream<CharT, Traits>

The class template basic_ifstream implements high-level input operations on file streams. It gives the high-level interface of std::basic_istream to a file-based stream buffer ( std::basic_filebuf ).

A typical implementation of std::basic_ifstream only holds one non-exported data member: an instance of std::basic_filebuf<CharT, Traits> .

 

Also defines two specializations for common character types:

type	definition
ifstream	basic_ifstream<char>
wifstream	basic_ifstream<wchar_t>

member function

construct file stream

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

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 a new file stream.

1) Default constructor: constructs a stream that is not associated with a file: constructs a std::basic_filebuf by default and constructs a base class that has members pointing to this default-constructed std::basic_filebuf.

2-3) First, perform the same steps as the default constructor, and then call rdbuf()->open(filename, mode | std::ios_base::in) (see std::basic_filebuf:: open ) to associate a stream with a file. If the open() call returns a null pointer, setstate(failbit) is set. Overload (3) is provided only if std::filesystem::path::value_type is not char. (since C++17)

4-5) 同 basic_ifstream(filename.c_str(), mode) 。

6) Move constructor: firstly, othermove to construct the base class from (this does not affect rdbuf()the pointer), then move to construct the std::basic_filebuf member, and then call this->set_rdbuf() to install a new as the basic_filebufrdbuf() pointer in the base class.

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

parameter

filename	-	filename to open
mode	-	Specifies the open mode. It is a bitmask type and defines the following constants: constant explain app Seek to end of stream before each write binary open in binary mode in open for reading out open for writing trunk Discards the contents of the stream on open ate Seeks to end of stream immediately after opening
other	-	Another file stream to use as source

call example

#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));
    return 0;
}

 

Destroy basic_ifstream and associated buffers, and close the file

The default destructor generated by basic_fstream will call the close method indirectly by calling the destructor of basic_filebuf. That is, the file is automatically closed on destruction.