Syntax highlight markdown change

.cpp

#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <algorithm>
#include <numeric>

using buffer_t = std::vector<char>;
using lines_t = std::vector<std::string>;

buffer_t read_file(const char* filepath)
{
	std::ifstream file(filepath);
	if (file.fail())
	{
		std::cout << "File not found: " << filepath << '\n';
		return {};
	}

	file.seekg(0, std::ios::end); // seek to the end

	int filesize = file.tellg(); // get the file size
	file.seekg(0, std::ios::beg);

	filesize -= file.tellg(); // reduce filesize by any header bytes

	buffer_t buffer;
	buffer.resize(filesize);

	file.read(buffer.data(), filesize);
	file.close();

	return buffer;
}

void write_file(const char* filepath, const std::string& data)
{
	static std::ofstream file;

	file.open(filepath);

	if (file.fail())
	{
		std::cout << "File not found: " << filepath << '\n';
		return;
	}

	file << data;
	file.close();
}

lines_t convert_to_lines(const buffer_t& buffer)
{
	lines_t lines;

	std::string line;
	line.reserve(100);

	std::for_each(
		std::cbegin(buffer), std::cend(buffer),
		[&line, &lines](const auto element) -> void
		{
			if (element != '\n')
				line += element;
			else
			{
				lines.push_back(line + element);
				line = "";
			}
		}
	);

	return lines;
}

std::string convert_to_string(const lines_t& lines, size_t size)
{
	std::string res;
	res.reserve(size);

	std::accumulate(
		std::cbegin(lines), std::cend(lines),
		false,
		[&res](const bool is_code, const auto& line) -> bool
		{
			if (line.size() >= 4 && line.substr(0, 4) == "    ")
			{
				if (!is_code)
					res += "```cpp\n";

				res += line.substr(4);
				return true;
			}
			else if (is_code && line == "\n")
			{
				res += line;
				return true;
			}
			else if (is_code)
				res += "```\n\n";

			res += line;
			return false;
		}
	);

	return res;
}

void update_syntax()
{
	const char* filepath = "E://Desktop//C--//C++//zz_Else//CppCoreGuidelines//CppCoreGuidelines.md";

	auto buffer = read_file(filepath);
	auto lines = convert_to_lines(buffer);
	auto s = convert_to_string(lines, buffer.size());

	write_file(filepath, s);
}

int main()
{
	update_syntax();

	return 0;
}