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File Handling in C


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File Handling in C++

In this blog, I’m explaining about file handling in C++

File: A File is a stream  of bytes stored on some secondary  storage device.

Text File: A text files stores information in  readable and printable form. Each line  of text is terminated with  an EOL End of line character.

Binary File: A binary file contains information in the non-readable form i.e. in the same formate in which it is held in memory.

 

File Stream

Stream: A stream is a general term used to name flow of data. Different streams are used to represent different kind of data flow.

There are three file I/O classes used for file read/write operation.

Ifstream : can be used for read operation.

Ofstream: can be used for write operation.

Fstream: can be used for both read and write operation.

 

Fstream.h

          1. This header file includes the definitions for the stream classes ifstream, ofstream and fstream. In C++ file input output facilities implemented through fstream.h header file.

2. It contain predefines set of operation  for handling  file related input and output, fstream class ties a file  to the  program for input and output operation.

A file can be opened using:

1.      By the constructor method. This will use default streams for file input or output. This method is preferred when file is opened in input or output mode only.

Example : ofstream file“student.dat”);   or ifstream file“student.dat”);

2.       By the open member function of the stream. It will preferred when file is opened in various modes i.e ios::in, ios::out, ios::app, ios::ate etc. e.g fstream file; file.open “book.dat”, ios::in | ios::out | ios::binary);

File modes:

ios::out It open file in output mode i.e write mode and place the file pointer in beginning, if file already exist it will overwrite the file.

ios::in It open file in input moderead mode and permit reading from the file.

ios::app It open the file in write mode, and place file pointer at the end of file i.e to add new contents and retains previous contents. If file does not exist it will create a new file.

 ios::ate It open the file in write or read mode, and place file pointer at the end of file i.e input/ output operations can performed anywhere in the file.

ios::trunc It truncates the existing file (empties the file.

 ios::nocreate If file does not exist this file mode ensures that no file is created and open fails.

ios::noreplace If file does not exist, a new file gets created but if the file already exists, the open( fails.

 ios::binary Opens a file in binary mode.

 eof: This function determines the end-of-file by returning truenon -zero) for end of file otherwise returning falsezero).

close: This function terminates the connection between the file and stream associated with it. Stream_object.close;    e.g file.clos e;

 Text File functions:

 Char I/O :

 get – read a single character from text file and store in a buffer. e.g file.getch;

  put - writing a single character in textfile  e.g. file.putch;

 getline - read a line of text from text file store in a buffer. e.g file.getlines,80);

We can also use file>>ch for reading and file<<ch writing  in text file. But >> operator does not accept white spaces.

Binary file functions:

1.      read - read a block of binary data or  reads a fixed number of bytes from the specified stream and store in a buffer.

2.       Syntax : Stream_object.read(char *& Object, sizeofObject; e.g  file.read(char *&s, sizeofs);

3.      write – write a block of binary data or writes fixed number of bytes from a specific memory location to  the specified stream. Syntax : Stream_object.writechar *)& Object, sizeofObject; e.g   file.writechar *)&s, sizeofs);

Note: Both functions take two arguments. • The first is the address of variable, and the second is the length of that variable in bytes. The address of variable must be type cast to type char*pointer to character type • The data written to a file using write ) can only be read accurately using read( ).

File Pointer: The file pointer indicates the position in the file at which the next input/output is to occur.

Moving the file pointer in a file for various operations viz modification, deletion , searching etc. Following functions are used:

 seekg: It places the file pointer to the specified position in input mode of file.

e.g file.seekg(p,ios::beg); or file.seekg -p,ios::end, or file.seekg(p,ios::cur i.e  to move to p byte  position from beginning, end or current position.

seekp: It places the file pointer to the specified position in output mode of file.

e.g file.seekpp,ios::beg); or file.seekp -p,ios::end, or file.seekpp,ios::cur

i.e  to move to p byte  position from beginning, end or current position.

tellg: This function returns the current working position of the file pointer in the input mode. e.g int p=file.tellg;

tellp: This function returns the current working position of the file pointer in the output mode. e.f int p=file.tellp;

Steps To Create a File

 1. Declare an object of the desired file stream class (ifstream, ofstream, or fstream

 2. Open the required file to be processed using constructor or open function.  Process the file. 3. Close the file stream using the object of file stream.

 

 

Example

using namespace System;

using namespace std;

int main(array<System::String ^> ^args)

{

             

            ofstream ofs("C:\\Users\\msclient001\\Desktop\\5-2-2015.txt",ios::app);

          if(ofs.good())

             {

             ofs<<"Hello a.txt, I'm appending this on you.";

              }

Console::ReadKey(0);

 

    return 0;

}


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