• C++读取MNIST数据集


    MNIST是一个标准的手写字符测试集。

    Mnist数据集对应四个文件:

    train-images-idx3-ubyte: training set images 
    train-labels-idx1-ubyte: training set labels 
    t10k-images-idx3-ubyte:  test set images 
    t10k-labels-idx1-ubyte:  test set labels

    训练数据集包含60000幅图片,测试集包含10000幅图片。


    文件格式:

    TRAINING SET LABEL FILE (train-labels-idx1-ubyte):
    [offset] [type]          [value]          [description] 
    0000     32 bit integer  0x00000801(2049) magic number (MSB first) 
    0004     32 bit integer  60000            number of items 
    0008     unsigned byte   ??               label 
    0009     unsigned byte   ??               label 
    ........ xxxx     unsigned byte   ??               label

    The labels values are 0 to 9.

    TRAINING SET IMAGE FILE (train-images-idx3-ubyte):

    [offset] [type]          [value]          [description] 
    0000     32 bit integer  0x00000803(2051) magic number 
    0004     32 bit integer  60000            number of images 
    0008     32 bit integer  28               number of rows 
    0012     32 bit integer  28               number of columns 
    0016     unsigned byte   ??               pixel 
    0017     unsigned byte   ??               pixel 
    ........ 
    xxxx     unsigned byte   ??               pixel

    Pixels are organized row-wise. Pixel values are 0 to 255. 0 means background (white), 255 means foreground (black).

    TEST SET LABEL FILE (t10k-labels-idx1-ubyte):

    [offset] [type]          [value]          [description] 
    0000     32 bit integer  0x00000801(2049) magic number (MSB first) 
    0004     32 bit integer  10000            number of items 
    0008     unsigned byte   ??               label 
    0009     unsigned byte   ??               label 
    ........ 
    xxxx     unsigned byte   ??               label

    The labels values are 0 to 9.

    TEST SET IMAGE FILE (t10k-images-idx3-ubyte):

    [offset] [type]          [value]          [description] 
    0000     32 bit integer  0x00000803(2051) magic number 
    0004     32 bit integer  10000            number of images 
    0008     32 bit integer  28               number of rows 
    0012     32 bit integer  28               number of columns 
    0016     unsigned byte   ??               pixel 
    0017     unsigned byte   ??               pixel 
    ........ 
    xxxx     unsigned byte   ??               pixel

    Pixels are organized row-wise. Pixel values are 0 to 255. 0 means background (white), 255 means foreground (black). 
      

    #include <iostream>
    #include <fstream>
    #include <string>
    #include <vector>
    using namespace std;
    
    int ReverseInt(int i)
    {
    	unsigned char ch1, ch2, ch3, ch4;
    	ch1 = i & 255;
    	ch2 = (i >> 8) & 255;
    	ch3 = (i >> 16) & 255;
    	ch4 = (i >> 24) & 255;
    	return((int)ch1 << 24) + ((int)ch2 << 16) + ((int)ch3 << 8) + ch4;
    }
    
    void read_Mnist_Label(string filename, vector<double>&labels)
    {
    	ifstream file(filename, ios::binary);
    	if (file.is_open())
    	{
    		int magic_number = 0;
    		int number_of_images = 0;
    		file.read((char*)&magic_number, sizeof(magic_number));
    		file.read((char*)&number_of_images, sizeof(number_of_images));
    		magic_number = ReverseInt(magic_number);
    		number_of_images = ReverseInt(number_of_images);
    		cout << "magic number = " << magic_number << endl;
    		cout << "number of images = " << number_of_images << endl;
    		
    	
    		for (int i = 0; i < number_of_images; i++)
    		{
    			unsigned char label = 0;
    			file.read((char*)&label, sizeof(label));
    			labels.push_back((double)label);
    		}
    		
    	}
    }
    
    void read_Mnist_Images(string filename, vector<vector<double>>&images)
    {
    	ifstream file(filename, ios::binary);
    	if (file.is_open())
    	{
    		int magic_number = 0;
    		int number_of_images = 0;
    		int n_rows = 0;
    		int n_cols = 0;
    		unsigned char label;
    		file.read((char*)&magic_number, sizeof(magic_number));
    		file.read((char*)&number_of_images, sizeof(number_of_images));
    		file.read((char*)&n_rows, sizeof(n_rows));
    		file.read((char*)&n_cols, sizeof(n_cols));
    		magic_number = ReverseInt(magic_number);
    		number_of_images = ReverseInt(number_of_images);
    		n_rows = ReverseInt(n_rows);
    		n_cols = ReverseInt(n_cols);
    
    		cout << "magic number = " << magic_number << endl;
    		cout << "number of images = " << number_of_images << endl;
    		cout << "rows = " << n_rows << endl;
    		cout << "cols = " << n_cols << endl;
    
    		for (int i = 0; i < number_of_images; i++)
    		{
    			vector<double>tp;
    			for (int r = 0; r < n_rows; r++)
    			{
    				for (int c = 0; c < n_cols; c++)
    				{
    					unsigned char image = 0;
    					file.read((char*)&image, sizeof(image));
    					tp.push_back(image);
    				}
    			}
    			images.push_back(tp);
    		}
    	}
    }
    
    int main()
    {
    	/*
    	vector<double>labels;
    	read_Mnist_Label("t10k-labels.idx1-ubyte", labels);
    	for (auto iter = labels.begin(); iter != labels.end(); iter++)
    	{
    		cout << *iter << " ";
    	}
    	*/
    	vector<vector<double>>images;
    	read_Mnist_Images("t10k-images.idx3-ubyte", images);
    	for (int i = 0; i < images.size(); i++)
    	{
    		for (int j = 0; j < images[0].size(); j++)
    		{
    			cout << images[i][j] << " ";
    		}
    	}
    	return 0;
    }






    Keep it simple!
    作者:N3verL4nd
    知识共享,欢迎转载。
  • 相关阅读:
    Linux命令-chmod、chown和chgrp
    UUID是如何保证全局唯一的
    Java实现HTML转换为PDF的常见方法
    Java内存溢出详解
    Java 版本6下载大全
    spring 标签
    java 静态成员访问
    Java开发之@PostConstruct执行顺序
    Java集合和数组的区别
    集合转数组的toArray()和toArray(T[] a)方法
  • 原文地址:https://www.cnblogs.com/lgh1992314/p/6616318.html
Copyright © 2020-2023  润新知