How to Read Whole ASCII File Into C++ std::string?

An ASCII file is a text file that has a standardized format so that information can be recognized and read easily by any platform or operating system. In C++, we represent the textual data as std::string objects. In this article, we will learn how to read a whole ASCII File into std::string in C++.

Read Whole ASCII File into C++ std::string

To read an entire ASCII file and save it into std::string, we can use the std::ifstream class to open and read the file with a combination of std::istreambuf_iterator to read the whole file content into a string.

Approach

1. First, open the file using std::ifstream file(filePath) that creates an input file stream for reading from the specified file.
2. Next, check if the file was opened successfully using the is_open() method. If the opening fails, print an error and return from the function.
3. Then, read the whole file into a string using std::istreambuf_iterator<char>(file) that creates an iterator to read characters from file from the beginning of the file.
4. Finally, close the file stream and print the populated string.

C++ Program to Read the Content of ASCII File into std::string

The below example demonstrates how we can read the content of an ASCII File into a std::string in C++.

C++

// C++ Program to read whole ASCII file into C++ std::string

#include <fstream>
#include <iostream>
#include <string>
using namespace std;

int main()
{
    // Replace "example.txt" with the path to your actual
    // file
    string filePath = "ascFile.txt";

    // Open the file using ifstream
    ifstream file(filePath);

    // Check if the file was opened successfully
    if (!file.is_open()) {
        cerr << "Failed to open file: " << filePath << endl;
        return 1; // Exit with error code if the file cannot
                  // be opened
    }

    // Read the whole file into a string
    string fileContent((istreambuf_iterator<char>(file)),
                       istreambuf_iterator<char>());

    // Close the file (optional here since the file will be
    // closed automatically when file goes out of scope)
    file.close();

    // Output the file content to the console
    cout << "File content:\n" << fileContent << endl;

    return 0;
}

Output

File content:
"New England", "Massachusetts", "Boston", "SuperMart",
"Feb" , 2000000"New England", "Massachusetts", "Springfield", "SuperMart",
"Feb" , 1400000"New England", "Massachusetts", "Worcester", "SuperMart",
"Feb" , 2200000

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