Xi IO flow

One Concept

One The concept of flow

1. Unstructured transmission of data

2. C++ flow （ External input computer , Computer output external , The process of input and output ）

3. C++11 standard ：I/O Standard class library

4. /*
   I：    in      Input 
   O：    out     Output 
    flow ：    Data flow 
   */

Two Use

fstream Common file operations class

One Common member functions

01 Open file open

Pattern mark	Applicable to	effect
ios::in	ifstream fstream	Open file for reading data . If the file doesn't exist , Then there is an error opening
ios::out	ofstream fstream	Open file for writing data . If the file doesn't exist , Then create a new file ; If the file exists originally , The original content is cleared when it is opened
ios::app	ofstream fstream	Open file , Used to add data at the end . If the file doesn't exist , Then create a new file
ios::ate	ifstream	Open an existing file , And will File read pointer Point to the end of the file . If the file doesn't exist , Then there is an error opening
ios::trunc	ofstream	When the file is opened, all data stored inside will be emptied , When used alone with ios::out identical
ios::binary	ifstream ofstream fstream	Open the file in binary mode . If this mode is not specified , Open... In text mode
ios::in | ios::out	fstream	Open an existing file , You can read its contents , You can also write data to it . When the file was first opened , The original content remains unchanged , If the file doesn't exist , Then there is an error opening
ios::in | ios::out	ofstream	Open an existing file , Data can be written to it . When the file was first opened , The original content remains unchanged , If the file doesn't exist , Then there is an error opening
ios::in | ios::out | ios::trunc	fstream	Open file , You can read its contents , You can also write data to it . If the file doesn't exist , Then create a new file ; If the file exists originally , The original content is cleared when it is opened

02 Operation file

//1. Judge whether the file is opened successfully 
obj.is_open();// Return value 
//2. Whether to reach the end of the file 
obj.eof();// Return value 
//3. write in ️ One   character 
obj.put('s');
//4. Read ️ One   character 
char ch = 0;
obj.get(ch);
ch = obj.get();
//5. Move file pointer 
/* Parameters ： Moving distance , Where to start moving */
/*
1 ios::beg  Beginning of file 
2 ios::end  End of file 
3 ios::cur  The current position 
*/
obj.seekp(2, ios::cur);
//6. Binary read-write file       Large and small end storage 
/*  Write  write */
obj.open("test.txt",ios::out);
int num = 0X11223344;
obj.write((const char*)&num,sizeof(int));
obj.close();
/*  read  read */
obj.open("test.txt",ios::in);
int val = 0;
obj.read((char*)&val,sizeof(int));
obj.close();
cout << hex << "val = 0X-" << val << endl;

03 Close file close

3、 ... and Using overloaded << >>

obj.open("test.txt",ios::out);
​
obj << "HAPPY NEW YEAR!" << endl;
obj << " May you be happy and prosperous " << endl;
obj << "10086" << endl;          //
​
obj.close();
obj.open("test.txt",ios::in);
​
char str_1[128];
char str_2[128];
int num;
obj >> str_1 >> str_2 >> num >> endl;
​
obj.close();