std::basic_ifstream::basic_ifstream(3)

NAME
std::basic_ifstream::basic_ifstream - std::basic_ifstream::basic_ifstream

Synopsis
   basic_ifstream(); (1)
   explicit basic_ifstream( const char* filename, (2)
   std::ios_base::openmode mode = ios_base::in );
   explicit basic_ifstream( const std::filesystem::path::value_type*
   filename, (3) (since C++17)
   std::ios_base::openmode mode = ios_base::in );
   explicit basic_ifstream( const std::string& filename, (4) (since C++11)
   std::ios_base::openmode mode = ios_base::in );
   template< class FsPath >
   explicit basic_ifstream( const FsPath& filename, (5) (since C++17)
   std::ios_base::openmode mode = ios_base::in );
   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).
   (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
              specifies stream open mode. Following constants and bit-wise OR between
              them may be used:
              Constant Explanation
   mode - 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));
 }
  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 3430 C++17 std::filesystem::path overload led to avoided by making it
                       unwanted conversions 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_istream<CharT,Traits>)