How Can I Get a File Size in C++?

Last Updated : 11 Feb, 2026

In C++, we often need to determine the size of a file which is the number of bytes in a file. This is done for various applications, such as file processing or validation. In this article, we will learn how to get the file size in C++.

Example:

Input:
FilePath = "C:/Users/Desktop/myFile.txt"

Output:
5 Bytes // myFile.txt contains "Hello"

How to Get a File's Size in C++?

In C++17 and later, we can use the std::filesystem::file_size() function from the std::filesystem library to get the size of a file. This function returns the size of the file in bytes, which can later be used for processing. It is a standalone function so we can call it directly by passing the path of the file as a parameter to the file_size() function.

C++ Program to Get File Size

The below program demonstrates how we can get a file size in C++.

C++ 
// C++ Program to demonstrate how we can get a file
// size from a file path

#include <filesystem>
#include <iostream>
using namespace std;

int main()
{
    // Define a path object representing the file path.
    filesystem::path filePath
        = "C:/Users/Desktop/myFile.txt";

    // Print the file size using the file_size() function
    // of the filesystem library.
    cout << "File size is: "
         << filesystem::file_size(filePath) << " bytes"
         << endl;
    return 0;
}

Output

File size is: 5 bytes

Note: file_size() is implemented using stat() on POSIX systems and GetFileSizeEx() on Windows, so the returned value reflects the logical file size in bytes, not the on-disk allocated size. Due to filesystem compression, sparse files, or platform/tool differences, this may not always match what some command-line tools report.

Note: The file_size() function works only in C++17 and later. If the file does not exist, it will throw a filesystem::filesystem_error exception.

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