std::ifstream::is_open() in C++ Last Updated : 22 Aug, 2024 Comments Improve Suggest changes Like Article Like Report The std::ifstream::is_open() function in C++ is a member function of the std::ifstream class, which is used to check if a file stream object has successfully opened a file for reading or not. This function returns a boolean value, true if the file stream is open and ready for I/O operations, and false otherwise.In this article, we will learn the std::ifstream::is_open() function, its syntax, how it works, and provide practical example to demonstrate its use in C++ file handling.Syntax of std::ifstream::is_open() in C++fileStream.is_open();Here, fileStream is an object of the std::ifstream class.Parameters of std::ifstream::is_open()The std::ifstream::is_open() function does not take any parameters.Return Value of std::ifstream::is_open()The return value of the std::ifstream::is_open() function indicates whether the file stream is open or not.It returns true if the file is successfully opened.It returns false if the file stream has not successfully opened a fileExample of std::ifstream::is_open() in C++The example below demonstrates how to use std::ifstream::is_open() in C++ to check if a file was successfully opened. After attempting to open a file with std::ifstream, we use is_open() to verify the success of the operation. Depending on the result, we can proceed with file operations or handle any errors. C++ // C++ program to use std::ifstream::is_open() in C++ to check if a file was successfully opened. #include <fstream> #include <iostream> using namespace std; int main(){ // Attempt to open the file "example.txt" for reading ifstream file("example.txt"); // Check if the file was successfully opened if (file.is_open()) { cout << "File opened successfully!" << endl; // Perform file operations here (e.g., reading from the file) } else { cout << "Failed to open file." << endl; } // Close the file to release resources file.close(); return 0; } OutputFile opened successfully!Time Complexity: O(1) as std::ifstream::is_open() simply checks the state of the file stream.Auxiliary Space: O(1), as it does not require any additional memory allocation. 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