C++ learning series---read file names and store them in txt and read each line of information from txt

【1】Read the file name under the sub-file and store it in TXT

(1) First understand a file structure:

struct _finddata_t {
    unsigned    attrib;
    time_t      time_create;   
    time_t      time_access;   
    time_t      time_write;
    _fsize_t    size;
    char        name[260];
};

The type of time_t is long.

The type of _fsize_t is unsigned long.

Now let’s explain the data members of the structure.

attrib is the attribute of the file being searched for:

_A_ARCH（存档）
_A_HIDDEN（隐藏）
_A_NORMAL（正常）
_A_RDONLY（只读）
_A_SUBDIR（子文件夹）
_A_SYSTEM（系统）

time_create, time_access and time_write are respectively the time when the file was created, the time when the file was last accessed and the time when the file was last modified.

size: file size.

name: file name.

(2). Use _findfirst and _findnext to find files (both functions are in io.h.)

1、_findfirst函数：long _findfirst(const char *, struct _finddata_t *);

The first parameter is the file name. You can use "*.*" to find all files, or you can use "*.cpp" to find .cpp files. The second parameter is the _finddata_t structure pointer. If the search is successful, the file handle is returned; if it fails, -1 is returned.

2、_findnext函数：int _findnext(long, struct _finddata_t *);

The first parameter is the file handle, and the second parameter is also the _finddata_t structure pointer. If the search is successful, 0 is returned, otherwise -1 is returned.

3. _findclose() function: int _findclose(long);

There is only one parameter, the file handle. If the shutdown is successful, it returns 0, and if it fails, it returns -1.

Note: Under win10 system, findnext will report an error when compiling, as shown in the figure:

Because the return type of _findnext() is intptr_t instead of long, data is lost when converting from "intptr_t" to "long". Just generally write:

long handle
改为
intptr_t handle
既可以运行

code show as below:

#include<iostream>
#include<fstream>
#include <io.h>
using namespace std;
const char *to_search = "E:\\opencv学习\\学习opencv源码\\official-code-in-the-learning-Opencv3-master\\calibration\\*.jpg";//欲查找的文件，支持通配符(可选择文件类型）
//可以指定查找所有文件\\*.*，也可以是指定文件\\*.格式类型
int main()
{
	//这里的handle句柄不要定义为long类型，否则_findnext会报错
	intptr_t handle;                                   //用于查找的句柄
	struct _finddata_t fileinfo;                       //文件信息的结构体
	handle = _findfirst(to_search,&fileinfo);          //第一次查找
	if (-1 == handle)return -1;
	if (fileinfo.attrib != _A_SUBDIR)//令文件的属性不属于子文件夹
		printf("%s\n", fileinfo.name);
	ofstream outdata;		//定义输出流
	outdata.open("E:\\list.txt", ios::app);//ios::app是尾部追加的意思
	outdata << fileinfo.name << endl;                   //打印出找到的文件的文件名
	while (!_findnext(handle, &fileinfo))               //循环查找其他符合的文件，知道找不到其他的为止
	{
		if (fileinfo.attrib != _A_SUBDIR)//
			printf("%s\n", fileinfo.name);
		//outdata.open("E:\\list.txt", ios::app);//ios::app是尾部追加的意思
		outdata << fileinfo.name << endl;
	}
	outdata.close();                                   //循环结束关闭输出流
	_findclose(handle);                                //别忘了关闭句柄
	system("pause");
	return 0;
}

【2】Read strings line by line from TXT

There are two main ways to read. Delimiters such as /t and /n can be recognized internally.

#include<iostream>
#include<fstream>
#include <io.h>
#include<string> //通过>>将流析取器传入字符串要用到该文件
using namespace std;
const char *to_search = "E:\\opencv学习\\学习opencv源码\\official-code-in-the-learning-Opencv3-master\\calibration\\*.jpg";//欲查找的文件，支持通配符(可选择文件类型）
//可以指定查找所有文件\\*.*，也可以是指定文件\\*.格式类型
int main()
{
	ifstream ifile;
	ifile.open("E:\\list.txt", ios::in );
	if (!ifile)
	{
		cout << "文件为打开" << endl;
	}

	//第一种方法读取
	//string str;		//将str改为char类型，可以按字符读取
	输入文件流
	//while (ifile >> str)
	//{
	//	
	//	cout << str  << endl;
	//}

	//第二种方法
	while (!ifile.eof())	//判断是否到txt截止符
	{
		string str;
		getline(ifile,str);
		cout << str << endl;
	}
	
	ifile.close();//不要忘记运行结束后关闭传入流

	system("pause");
	return 0;
}
关于传入传出流是相对于VS操作而言，从外部到VS是传入，从vs到外部为传出。