C++ learning-4 query the C++ standard library and write application layer code to filestream [lack of analysis of the standard library]

1. View the three-way
man manual of the C++ standard library , but Ubuntu does not install it by default, you need to install it manually, but it is not convenient to view it under linux.
Two URLs are introduced;
English is old but complete; http://cplusplus.com/reference/fstream/basic_fstream/
Chinese and updated to 20; https://zh.cppreference.com/w/cpp/io/basic_fstream

Take the filestream that reads and writes files as an example; it is
written according to the C++ standard library web page reference.
Note that errors may be reported, you can use g++ 3.10 Filestream.cpp -std=c++11, you can use C++11 standard

#include <iostream>
#include <fstream>
#include <string>

using namespace std;
int main()
{
    
    
	string str_fileName = "1.txt";
	
	//原型void open( const char *filename,ios_base::openmode mode = ios_base::in|ios_base::out );
	std::fstream s(str_fileName);//其操作结果不以返回值来返回而是存在在内部用is_open()
	//bool is_open();	若文件流有关联文件，则为 true ，否则为 false 。
	if(!s.is_open())
	{
    
    
		cout<<"operator error"<<endl;
	}
	//basic_ostream& write( const char_type* s, std::streamsize count );	
	s.write("1234", 5);
	
	s.close();
	
	return 0;
}

2. There is a lack of a large number of analysis and other function use cases, which will be added later, because it involves complex source code and template-related content