std::basic_fstream<CharT,Traits>::is_open (3) - Linux Manuals

std::basic_fstream<CharT,Traits>::is_open: std::basic_fstream<CharT,Traits>::is_open

NAME

std::basic_fstream<CharT,Traits>::is_open - std::basic_fstream<CharT,Traits>::is_open

Synopsis

bool is_open(); (until C++11)
bool is_open() const; (since C++11)

Checks if the file stream has an associated file.
Effectively calls rdbuf()->is_open().

Parameters

(none)

Return value

true if the file stream has an associated file, false otherwise

Example

// Run this code

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

  int main()
  {
      std::string filename = "some_file";

      std::fstream fs(filename, std::ios::in);

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

      if(!fs.is_open())
      {
         fs.clear();
         fs.open(filename, std::ios::out);
         std::cout << "fs.is_open() = " << fs.is_open() << '\n';
      }
  }

Possible output:

  fs.is_open() = false
  fs.is_open() = true