std::basic_fstream<CharT,Traits>::open
From cppreference.com
< cpp | io | basic fstream
|
void open(
const
char
* filename,
= std::ios_base::in | std::ios_base::out ) ; |
(1) | |
|
void open(
const std::
filesystem
::
path
::
value_type
* filename,
= std::ios_base::in | std::ios_base::out ) ; |
(2) | (since C++17) |
|
void open(
const
std::string
& filename,
= std::ios_base::in | std::ios_base::out ) ; |
(3) | (since C++11) |
|
void open(
const
std::filesystem::path
& filename,
= std::ios_base::in | std::ios_base::out ) ; |
(4) | (since C++17) |
Opens and associates the file with name filename with the file stream.
Calls clear() on success. Calls setstate(failbit)
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 | ||||||||||||||||
| mode | - | specifies stream open mode. It is a BitmaskType, the following constants are defined:
|
Return value
(none)
Example
Run this code
#include <fstream> #include <iostream> #include <string> 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'; }
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 22 | C++98 | it was unclear how error state changes upon a successful open | the error state is unchanged |
| LWG 409 | C++98 | the error state was unchanged upon a successful open | it is cleared[1] |
| LWG 460 | C++98 | the default argument of mode in overload (1)
was missing (it is present in the synopsis |
added |
- ↑ The resolution of LWG issue #22 is overriden.
See also
| checks if the stream has an associated file (public member function) |
|
| closes the associated file (public member function) |
|
| opens a file and configures it as the associated character sequence (public member function of std::basic_filebuf<CharT,Traits>) |