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

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// 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)