C++

Reference

<fstream>

basic_ifstream

public member function
<fstream>

std::basic_ifstream::is_open

bool is_open();
bool is_open() const;
Check if 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

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
 
// ifstream::is_open
#include <iostream>     // std::cout
#include <fstream>      // std::ifstream

int main () {
  std::ifstream ifs ("test.txt");

  if (ifs.is_open()) {
    // print file:
    char c = ifs.get();
    while (ifs.good()) {
      std::cout << c;
      c = ifs.get();
    }
  }
  else {
    // show message:
    std::cout << "Error opening file";
  }

  return 0;
}

Data races

Accesses the basic_ifstream 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

basic_ifstream::open
Open file (public member function)
basic_ifstream::close
Close file (public member function)
basic_filebuf::is_open
Check if file is open (public member function)