C++ File Handling:: open()














































C++ File Handling:: open()



                                        Opening a File


The first operation performed on an object of one of these classes is to associate it to a real file. This procedure is known to open a file.

  We can open a file using any one of the following methods:

    1. First is bypassing the file name in constructor at the time of object creation.
    2. Second is using the open() function.

To open a file use

  • open() function
   Syntax

  • void open(const char* file_name,ios::openmode mode);
  Example

fstream new_create1;
new_create1.open("newfilehasopen.txt", ios::out);


In the above example, new_create1 is an object of type fstream, as we know fstream is a class so we need to create an object of this class to use its member functions. So we create 
new_create1 object and call open()function.

 Here we use out mode that allows us to open the file to write in it.


Default Open Modes :

  • ifstream ios::in
  • ofstream ios::out
  • fstream ios::in | ios::out

We can combine the different modes using or symbol | .

  Example

     ofstream new_file;

  • new_create1.open("newfilehasopen.txt", ios::out | ios::app );
Here, input mode and append mode are combined which represents the file is opened for writing and appending the outputs at the end.

       Example of opening/creating a file using the open() function

  #include<iostream>
  #include <fstream>
   using namespace std;
  int main()
  {
   fstream new_create1; 
   new_create1.open("new_create1",ios::out);  
   if(!new_create1) 
  cout<<"File  has been failed to create";
  else
  {
    cout<<"New file has been created";
    new_create1.close(); 
   }
  return 0;
}



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