How to Read File into String in C++?

Last Updated : 21 May, 2024

In C++, file handling allows us to read and write data to an external file from our program. In this article, we will learn how to read a file into a string in C++.

Reading Whole File into a C++ String

To read an entire file line by line and save it into std::string, we can use std::ifstream class to create an input file stream for reading from the specified file with a combination of std::getline to extract the lines from the file content that can be concatenated and stored in a string variable.

Approach

Open the file using std::ifstream file(filePath).
Use the is_open() method to check if the file was opened successfully, if not print error message and return.
Use a loop with std::getline(file, line) to read each line of the file into a string and print the populated string.
Close the file stream.

C++ Program to Read a File into String

The below program demonstrates how we can read the content of a file into a std::string line by line in C++.

C++

// C++ Program to demonstrate how to Read a File into String #include <fstream> #include <iostream> #include <string> using namespace std;  int main() {      // get the filepath     string filePath = "myFile.txt";      // Open the file using ifstream     ifstream file(filePath);      // confirm file opening     if (!file.is_open()) {         // print error message and return         cerr << "Failed to open file: " << filePath << endl;          return 1;     }      // Read the file line by line into a string     string line;     while (getline(file, line)) {         cout << line << endl;     }      // Close the file     file.close();      return 0; }

Output

File Content:   Hi, Geek!  Welcome to gfg.  Happy Coding ;)

Time Complexity: O(n), here n is total number of characters in the file.
Auxiliary Space: O(n)

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How to Read File into String in C++?

Reading Whole File into a C++ String

Approach

C++ Program to Read a File into String

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