MNIST C++ IO Helper Header

mnist.h

#pragma once
#include <string>
#include <opencv/cv.hpp>
using namespace cv;
using namespace std; 
uchar** read_mnist_images(string full_path, int& number_of_images, int& image_size) {
	auto reverseInt = [](int i) {
		unsigned char c1, c2, c3, c4;
		c1 = i & 255, c2 = (i >> 8) & 255, c3 = (i >> 16) & 255, c4 = (i >> 24) & 255;
		return ((int)c1 << 24) + ((int)c2 << 16) + ((int)c3 << 8) + c4;
	};
	typedef unsigned char uchar;
	ifstream file(full_path, ios::binary);
	if (file.is_open()) {
		int magic_number = 0, n_rows = 0, n_cols = 0;
		file.read((char *)&magic_number, sizeof(magic_number));
		magic_number = reverseInt(magic_number);
		if (magic_number != 2051) throw runtime_error("Invalid MNIST image file!");
		file.read((char *)&number_of_images, sizeof(number_of_images)), number_of_images = reverseInt(number_of_images);
		file.read((char *)&n_rows, sizeof(n_rows)), n_rows = reverseInt(n_rows);
		file.read((char *)&n_cols, sizeof(n_cols)), n_cols = reverseInt(n_cols);
		image_size = n_rows * n_cols;
		uchar** _dataset = new uchar*[number_of_images];
		for (int i = 0; i < number_of_images; i++) {
			_dataset[i] = new uchar[image_size];
			file.read((char *)_dataset[i], image_size);
		}
		return _dataset;
	}
	else {
		throw runtime_error("Cannot open file `" + full_path + "`!");
	}
}
bool write_mnist_perlin_images(string full_path, uchar** _dataset, int& number_of_images, int& image_size) {
	typedef unsigned char uchar;
	ofstream file(full_path, ios::binary);
	if (file.is_open()) {
		for (int i = 0; i < number_of_images; i++) {
			file.write((char *)_dataset[i], image_size);
		}
		return true;
	}
	else {
		throw runtime_error("Cannot open file `" + full_path + "`!");
	}
}
uchar** read_mnist_perlin_images(string _full_path) {
	const int number_of_images = 10000; 
	const int image_size = 28 * 28; 
	ifstream file(_full_path, ios::binary);
	if (file.is_open()) {
		uchar** _dataset = new uchar*[number_of_images];
		for (int i = 0; i < number_of_images; i++) {
			_dataset[i] = new uchar[image_size];
			file.read((char *)_dataset[i], image_size);
		}
		return _dataset;
	}
	else {
		throw runtime_error("Cannot open file `" + _full_path + "`!");
	}
}
uchar convertImage(uchar** imgs, uchar* labels, int id, int image_size, Mat &img) {
	int w = int(round(sqrt(image_size)));
	img = Mat(w, w, CV_8UC1, imgs[id]); 
	return labels[id];
}
uchar* read_mnist_labels(string full_path, int& number_of_labels) {
	auto reverseInt = [](int i) {
		unsigned char c1, c2, c3, c4;
		c1 = i & 255, c2 = (i >> 8) & 255, c3 = (i >> 16) & 255, c4 = (i >> 24) & 255;
		return ((int)c1 << 24) + ((int)c2 << 16) + ((int)c3 << 8) + c4;
	};
	typedef unsigned char uchar;
	ifstream file(full_path, ios::binary);
	if (file.is_open()) {
		int magic_number = 0;
		file.read((char *)&magic_number, sizeof(magic_number));
		magic_number = reverseInt(magic_number);
		if (magic_number != 2049) throw runtime_error("Invalid MNIST label file!");
		file.read((char *)&number_of_labels, sizeof(number_of_labels)), number_of_labels = reverseInt(number_of_labels);
		uchar* _dataset = new uchar[number_of_labels];
		for (int i = 0; i < number_of_labels; i++) {
			file.read((char*)&_dataset[i], 1);
		}
		return _dataset;
	}
	else {
		throw runtime_error("Unable to open file `" + full_path + "`!");
	}
}