C + + file stream operations must be known

One, file stream operation

1. Determine the mode in which the file opens. The main modes to choose from are:

Ios::in open a file for input (read)
Ios::out Open file for output (write)
Ios::ate initial Position: End of File
Ios::app all outputs appended to the end of the file
Ios::trunc if the file already exists, delete the file first
Ios::binary binary mode

2. By default, the file is written as text, and the data in the original file is deleted, i.e. Ios::trunc

3. Determine if the file is open properly. The good file operation habit is that each time a file is opened, before the file is written to determine whether the file is open normally, the function used is is_open ().

4. Write the file. There are three main functions,<< stream operator, write a character put (), write a piece of data writing;

std::ostream::operator<<
Std::ostream::p UT
Std::ostream::write

5. File read. The main stream operator >>, read a character get, read a line of getline, read a file

Std::istream::operator>>
istream& operator>> (int& val);
Std::istream::getline
istream& Getline (char* s, streamsize N);
istream& Getline (char* s, streamsize N, Char Delim);
Std::getline (String)
istream& Getline (istream& is, string& str, char delim);
istream& Getline (istream& is, string& str);
Std::istream::read
istream& Read (char* s, streamsize N);
Std::istream::get
istream& get (char& c);

6. End of file judgment infile.eof ()

7. File Close infile.close ()

8. File location seekp (), SEEKG ()

9. File modification, see example

1.1 File Write

#include <string>#include<iostream>#include<fstream>using namespacestd;intMain () {/** Ios::app: Add, Ios::trunc: If the file exists, first delete the file (default) * bios::binary binary Read-write, default is text mode*/ofstream outfile ("testfile.txt"Ios:: out|Ios::trunc); if(!Outfile.is_open ()) {Cerr<<"file cannot open!"<<Endl; return-1; } outfile<<"This is a test.\n"; OutFile<< -<<Endl; Outfile.put ('C');//write a char.Outfile.put ('\ n'); Charbuffer[1024x768] ="ABC"; Outfile.write (Buffer,sizeof(buffer));//write a block.Outfile.close (); return 0;}

1.2 File read

#include<string>#include<iostream>#include<fstream>using namespacestd;intMain () {Ifstream infile ("testfile.txt"); if(!Infile.is_open ()) {Cerr<<"file cannot open!"<<Endl; return-1; }    //read a character    Charch; InFile.Get(CH); //read a string    stringWord; InFile>>Word; //read a line commonly usedINFILE.SEEKG (0); stringLine ;    Getline (infile, line); Charbuffer[1024x768]; INFILE.SEEKG (0);//Navigate to File headerInfile.getline (Buffer,sizeof(buffer)); //Read File BlockINFILE.SEEKG (0); Infile.read (Buffer,sizeof(buffer)); //determine end of fileINFILE.SEEKG (0);  while(!infile.eof ()) {getline (infile,line);//infile >> Word;//Infile.read (buffer,sizeof (buffer));} infile.close (); return 0;}

1.3 File Content Modification

#include <fstream>usingnamespace  std; int Main () {    fstream inoutfile ("testfile.txt", iOS:: in | iOS::out);    INOUTFILE.SEEKG (+);     " It's easy to modify the file! \ n";    Inoutfile.close ();     return 0 ;}

C + + file stream operations must be known