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• C++ Read Data From File
• C++ Read Files In Directory
• C++ Read File To String
• How To Read File In Java
• C++ Read All File

Reading a File. To read the file, we must open it first using any of the mode, for example if you only want to read the file then open it in “r” mode. Based on the mode selected during file opening, we are allowed to perform certain operations on the file. C Program to read a file. May 13, 2012  hi guys, i need to extract data in txt file. Im using dev c. For example this type of data X Y 12.3 4.4 23.6 5 78.3 8.2. C read file program: This C language program reads a file whose name is entered by a user and displays its contents on the screen. Function fopen is used to open a file; it returns a pointer to structure FILE which is a predefined structure in 'stdio.h' header file.

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C++ Read Data From File

So far, we have been using the iostream standard library, which provides cin and cout methods for reading from standard input and writing to standard output respectively.

This tutorial will teach you how to read and write from a file. This requires another standard C++ library called fstream, which defines three new data types −

To perform file processing in C++, header files <iostream> and <fstream> must be included in your C++ source file.

Opening a File

A file must be opened before you can read from it or write to it. Either ofstream or fstream object may be used to open a file for writing. And ifstream object is used to open a file for reading purpose only.

Following is the standard syntax for open() function, which is a member of fstream, ifstream, and ofstream objects.

Here, the first argument specifies the name and location of the file to be opened and the second argument of the open() member function defines the mode in which the file should be opened.

You can combine two or more of these values by ORing them together. For example if you want to open a file in write mode and want to truncate it in case that already exists, following will be the syntax −

Similar way, you can open a file for reading and writing purpose as follows −

Closing a File

C++ Read Files In Directory

When a C++ program terminates it automatically flushes all the streams, release all the allocated memory and close all the opened files. But it is always a good practice that a programmer should close all the opened files before program termination.

Following is the standard syntax for close() function, which is a member of fstream, ifstream, and ofstream objects.

Writing to a File

C++ Read File To String

While doing C++ programming, you write information to a file from your program using the stream insertion operator (<<) just as you use that operator to output information to the screen. The only difference is that you use an ofstream or fstream object instead of the cout object.

Reading from a File

You read information from a file into your program using the stream extraction operator (>>) just as you use that operator to input information from the keyboard. The only difference is that you use an ifstream or fstream object instead of the cin object.

Read and Write Example

Following is the C++ program which opens a file in reading and writing mode. After writing information entered by the user to a file named afile.dat, the program reads information from the file and outputs it onto the screen −

When the above code is compiled and executed, it produces the following sample input and output −

Above examples make use of additional functions from cin object, like getline() function to read the line from outside and ignore() function to ignore the extra characters left by previous read statement.

File Position Pointers

How To Read File In Java

Both istream and ostream provide member functions for repositioning the file-position pointer. These member functions are seekg ('seek get') for istream and seekp ('seek put') for ostream.

The argument to seekg and seekp normally is a long integer. A second argument can be specified to indicate the seek direction. The seek direction can be ios::beg (the default) for positioning relative to the beginning of a stream, ios::cur for positioning relative to the current position in a stream or ios::end for positioning relative to the end of a stream.

C++ Read All File

The file-position pointer is an integer value that specifies the location in the file as a number of bytes from the file's starting location. Some examples of positioning the 'get' file-position pointer are −