C++ 读取txt文件方法读取速度比较

深碍√TFBOYSˉ_ 2023-07-13 13:51 10阅读 0赞

测试程序部分如下：

文本文档中每一行代表一个三维坐标的x，y，z值，中间使用空格隔开

![20200312165014529.png][]

// fread.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
    //
    //  read1  采用fread函数，按字符分配到vector数组
    //  read2  getline按行读取数据，按字符分配到vector数组
    //  read3  getline按行读取数据，按字符串分配到vector
    //  read4  fin按行读取数据，按字符串分配到vector
    //  read5  采用fread函数，按字符串分配到vector
    #include "pch.h"
    #include <iostream>
    #include<vector>
    #include <stdio.h>
    #include <stdlib.h>
    #include<ctime>
    #include<fstream>
    #include<string>
    #include<sstream>
    #include<cassert>
    using namespace std;
    double str2num(const string str)
    {
    	stringstream ss(str);
    	double num;
    	ss >> num;
    	return num;
    }
    struct Point
    {
    	double x;
    	double y;
    	double z;
    };
    vector<Point> read1(const char * file)
    {
    	FILE* pFile;   //文件指针
    	long lSize;   // 用于文件长度
    	char* buffer; // 文件缓冲区指针
    	size_t result;  // 返回值是读取的内容数量
    	vector<string> v;
    
    	pFile = fopen(file, "rb");
    	if (pFile == NULL) { fputs("File error", stderr); exit(1); }    // 如果文件错误，退出1
    
    	// obtain file size:  获得文件大小
    	fseek(pFile, 0, SEEK_END); // 指针移到文件末位
    	lSize = ftell(pFile);  // 获得文件长度
    	rewind(pFile);  // 函数rewind()把文件指针移到由stream(流)指定的开始处, 同时清除和流相关的错误和EOF标记
    
    	// allocate memory to contain the whole file: 为整个文件分配内存缓冲区
    	buffer = (char*)malloc(sizeof(char) * lSize); // 分配缓冲区，按前面的 lSize
    	if (buffer == NULL) { fputs("Memory error", stderr); exit(2); }  // 内存分配错误，退出2
    
    	// copy the file into the buffer:  该文件复制到缓冲区
    	result = fread(buffer, 1, lSize, pFile); // 返回值是读取的内容数量
    	if (result != lSize) { fputs("Reading error", stderr); exit(3); } // 返回值如果不和文件大小，读错误
    
    	/* the whole file is now loaded in the memory buffer. */ //现在整个文件载入内存缓冲区
    
    	// 读到内存，看自己怎么使用了...............
    	// ...........
    	//cout << buffer;
    
    	v.push_back(buffer);
    	cout << "文件大小：  " << v[0].size() << endl;
    	vector<Point>num;
    	int i = 0;
    	while (i < v[0].size())
    	{
    		Point p;
    		string num_s = "";
    		while (v[0][i] != ' ')
    		{
    			num_s += v[0][i];
    			i++;
    		}
    		p.x = str2num(num_s);
    		i++;
    		num_s = "";
    		while (v[0][i] != ' ')
    		{
    			num_s += v[0][i];
    			i++;
    		}
    		p.y = str2num(num_s);
    		i++;
    		num_s = "";
    		while (v[0][i] != ' ')
    		{
    			num_s += v[0][i];
    			i++;
    		}
    		p.z = str2num(num_s);
    		num.push_back(p);
    		while ((v[0][i] != '\n') && (i < v[0].size()))
    		{
    			i++;
    		}
    		i++;
    	}
    
    	// terminate // 文件终止
    
    	fclose(pFile);
    
    	free(buffer);
    }
    vector<Point> readTxt2(string file)
    {
    	std::cout << "读取数据中..." << endl;
    	ifstream infile;
    	infile.open(file.data());   //将文件流对象与文件连接起来 
    	assert(infile.is_open());   //若失败,则输出错误消息,并终止程序运行 
    
    	string s;
    	//char str;
    	vector<string> ve;
    	vector<Point> num;
    	while (getline(infile, s))
    	{
    		Point p;
    		int i = 0;
    		string num_s = "";
    		while (s[i] != ' ')
    		{
    			num_s += s[i];
    			i++;
    		}
    		p.x = str2num(num_s);
    		i++;
    		num_s = "";
    		while (s[i] != ' ')
    		{
    			num_s += s[i];
    			i++;
    		}
    		p.y = str2num(num_s);
    		i++;
    		num_s = "";
    		while (s[i] != ' ')
    		{
    			num_s += s[i];
    			i++;
    		}
    		p.z = str2num(num_s);
    		num.push_back(p);
    	}
    
    	infile.close();             //关闭文件输入流 
    	std::cout << "读取文件完毕..." << endl;
    	return num;
    }
    vector<Point> read3(string file)
    {
    	ifstream fin(file.c_str(), ios::in);
    	char     line[500];
    	string   x, y, z;
    	vector<Point>num;
    	while (fin.getline(line, sizeof(line)))
    	{
    		stringstream words(line);   //将读取到的某一行字符串以空格区分开，
                                        // 就是x，y，z坐标写在一行，以空格隔开就可以
    
    		words >> x;
    		words >> y;
    		words >> z;
    
    		Point point;
    		point.x = atof(x.c_str());
    		point.y = atof(y.c_str());
    		point.z = atof(z.c_str());
    
    		num.push_back(point);
    	}
    	return num;
    }
    vector<Point> read4(string file)
    {
    	ifstream fin(file);
    	string   x, y, z;
    	string temp;
    	vector<Point>num;
    	while (fin >> temp)
    	{
    		stringstream words(temp);
    
    		words >> x;
    		words >> y;
    		words >> z;
    
    		Point point;
    		point.x = atof(x.c_str());
    		point.y = atof(y.c_str());
    		point.z = atof(z.c_str());
    
    		num.push_back(point);
    	}
    	return num;
    }
    vector<Point> read5(const char * file)
    {
    	FILE* pFile;   //文件指针
    	long lSize;   // 用于文件长度
    	char* buffer; // 文件缓冲区指针
    	size_t result;  // 返回值是读取的内容数量
    	vector<string> v;
    
    	pFile = fopen(file, "rb");
    	if (pFile == NULL) { fputs("File error", stderr); exit(1); }    // 如果文件错误，退出1
    
    	// obtain file size:  获得文件大小
    	fseek(pFile, 0, SEEK_END); // 指针移到文件末位
    	lSize = ftell(pFile);  // 获得文件长度
    	rewind(pFile);  // 函数rewind()把文件指针移到由stream(流)指定的开始处, 同时清除和流相关的错误和EOF标记
    
    	// allocate memory to contain the whole file: 为整个文件分配内存缓冲区
    	buffer = (char*)malloc(sizeof(char) * lSize); // 分配缓冲区，按前面的 lSize
    	if (buffer == NULL) { fputs("Memory error", stderr); exit(2); }  // 内存分配错误，退出2
    
    	// copy the file into the buffer:  该文件复制到缓冲区
    	result = fread(buffer, 1, lSize, pFile); // 返回值是读取的内容数量
    	if (result != lSize) { fputs("Reading error", stderr); exit(3); } // 返回值如果不和文件大小，读错误
    
    	/* the whole file is now loaded in the memory buffer. */ //现在整个文件载入内存缓冲区
    
    	v.push_back(buffer);
    	vector<Point>num;
    	string   x, y, z;
    	for (int i = 0; i < v[0].size(); i++)
    	{
    		string str = "";
    		if (v[0][i] != '\n')
    		{
    			str += v[0][i];
    			i++;
    		}
    		stringstream words(str);
    		words >> x;
    		words >> y;
    		words >> z;
    		Point point;
    		point.x = atof(x.c_str());
    		point.y = atof(y.c_str());
    		point.z = atof(z.c_str());
    
    		num.push_back(point);
    	}
    	// terminate // 文件终止
    
    	fclose(pFile);
    	free(buffer);
    	return num;
    }
    int main()
    {
    	float start = clock();
    	vector<Point> num1 = read1("E:\\data_test\\option-0000.txt");
    	cout << "read1函数读取用时 ： " << clock() - start << endl;
    	start = clock();
    	vector<Point> num2 = readTxt2("E:\\data_test\\option-0000.txt");
    	cout << "read2函数读取用时 ： " << clock() - start << endl;
    	start = clock();
    	vector<Point> num3 = read3("E:\\data_test\\option-0000.txt");
    	cout << "read3函数读取用时 ： " << clock() - start << endl;
    	start = clock();
    	vector<Point> num4 = read4("E:\\data_test\\option-0000.txt");
    	cout << "read4函数读取用时 ： " << clock() - start << endl;
    	start = clock();
    	vector<Point> num5 = read5("E:\\data_test\\option-0000.txt");
    	cout << "read5函数读取用时 ： " << clock() - start << endl;
    }

原文地址：[https://blog.csdn.net/qq\_33519317/article/details/98524441][https_blog.csdn.net_qq_33519317_article_details_98524441]

[20200312165014529.png]: /images/20230529/9c798aa959bc4585bde9773649d60d2c.png
[https_blog.csdn.net_qq_33519317_article_details_98524441]: https://blog.csdn.net/qq_33519317/article/details/98524441