C++

Reference

<fstream>

fstream

public member function
<fstream>

std::fstream::is_open

bool is_open();
bool is_open() const;
Check if a file is open
Returns whether the stream is currently associated to a file.

Streams can be associated to files by a successful call to member open or directly on construction, and disassociated by calling close or on destruction.

The file association of a stream is kept by its internal stream buffer:
Internally, the function calls rdbuf()->is_open()

Parameters

none

Return Value

true if a file is open and associated with this stream object.
false otherwise.

Example

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// fstream::is_open
#include <iostream>     // std::cout
#include <fstream>      // std::fstream

int main () {
  std::fstream fs;
  fs.open ("test.txt");
  if (fs.is_open())
  {
    fs << "lorem ipsum";
    std::cout << "Operation successfully performed\n";
    fs.close();
  }
  else
  {
    std::cout << "Error opening file";
  }
  return 0;
}

Possible output:
Operation successfully performed


Data races

Accesses the fstream object.
Concurrent access to the same stream may introduce data races.

Exception safety

Strong guarantee: if an exception is thrown, there are no changes in the stream.

See also

fstream::open
Open file (public member function)
fstream::close
Close file (public member function)
filebuf::is_open
Check if a file is open (public member function)