std::basic_fstream::open

Parameters

filename

String with the name of the file to open.
Specifics about its format and validity depend on the library implementation and running environment.

mode

Flags describing the requested input/output mode for the file.
This is an object of the bitmask member type openmode that consists of a combination of the following member constants:

member constant	stands for	access
in	input	File open for reading: the internal stream buffer supports input operations.
out	output	File open for writing: the internal stream buffer supports output operations.
binary	binary	Operations are performed in binary mode rather than text.
ate	at end	The output position starts at the end of the file.
app	append	All output operations happen at the end of the file, appending to its existing contents.
trunc	truncate	Any contents that existed in the file before it is open are discarded.

These flags can be combined with the bitwise OR operator (|).

If the mode has both trunc and app set, the opening operation fails. It also fails if either is set but out is not, or if both app and in are set.

If the mode has both trunc and app set, the opening operation fails. It also fails if trunc is set but out is not.

Return Value

Example

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// fstream::open / fstream::close
#include <fstream>      // std::fstream
int main () {
  std::fstream fs;
  fs.open ("test.txt", std::fstream::in | std::fstream::out | std::fstream::app);
  fs << " more lorem ipsum";
  fs.close();
  return 0;
}

Data races

Exception safety

See also

basic_fstream::is_open

Check if file is open (public member function)

basic_fstream::close

Close file (public member function)

basic_filebuf::open

Open file (public member function)