NAME¶

std::basic_fstream::open - std::basic_fstream::open

Synopsis¶

void open( const char *filename, (1)
ios_base::openmode mode = ios_base::in|ios_base::out );
void open( const std::filesystem::path::value_type *filename, (2) (since C++17)
ios_base::openmode mode = ios_base::in|ios_base::out );
void open( const std::string &filename, (3) (since C++11)
ios_base::openmode mode = ios_base::in|ios_base::out );
void open( const std::filesystem::path &filename, (4) (since C++17)
ios_base::openmode mode = ios_base::in|ios_base::out );

Opens and associates the file with name filename with the file stream.

Calls setstate(failbit) on failure.

Calls clear() on success. (since C++11)

1-2) Effectively calls rdbuf()->open(filename, mode). (see std::basic_filebuf::open
for the details on the effects of that call).
Overload (2) is only provided if std::filesystem::path::value_type is not char.
(since C++17)
3-4) Effectively calls (1-2) as if by open(filename.c_str(), mode).

Parameters¶

filename - the name of the file to be opened
specifies stream open mode. It is bitmask type, the following constants
are defined:

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

Return value¶

(none)

Example¶

// Run this code

#include <string>
#include <fstream>
#include <iostream>

int main()
{
std::string filename = "example.123";

std::fstream fs;

fs.open(filename);

if(!fs.is_open())
{
fs.clear();
fs.open(filename, std::ios::out); //Create file.
fs.close();
fs.open(filename);
}

std::cout << std::boolalpha;
std::cout << "fs.is_open() = " << fs.is_open() << '\n';
std::cout << "fs.good() = " << fs.good() << '\n';
}

See also¶

is_open checks if the stream has an associated file
(public member function)
close closes the associated file
(public member function)
open opens a file and configures it as the associated character sequence
(public member function of std::basic_filebuf<CharT,Traits>)