How to Read File into String in C++?
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++ 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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