File management in C++
- 2. What is a File? A file is bunch of bytes stored on some storage device like tape, magnetic disk etc.
- 3. C++ File Classes In C++, file input/output facilities are implemented using three classes- 1. fstream: Stream class to both read and write from/to files. 2. ifstream: Stream class to read from files 3. ofstream: Stream class to write on files
- 4. fstream header file The C++ input/output operations are very much similar to the console input and output operations. The file operations also make use of streams as an interface between the programs and the files. A stream is a general name given to a flow of data at the lowest level. A stream can be just defined as a sequence of bytes.
- 5. File Input Output Streams From the above figure we can see that the stream that supplies data to the program is known as input stream. It reads the data from the file and hands it over to the program. The stream that receives data from the program is known as output stream. It writes the received data to the files.
- 6. Storage of Data Files Data files can be stored in two ways- 1. Text file – This file stores information in ASCII characters. In text files, each line of text is terminated with a special character known as EOL(End of line) character. 2. Binary file - It contains information in the same format in which the information is held in memory . In binary files , there is no delimiter for the line. Also no translation occurs in binary files.
- 7. 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. Syntax- void open(const char *filename, ios::openmode mode); 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.
- 8. S.No Mode Flag & Description 1 ios::app Append mode. All output to that file to be appended to the end. 2 ios::ate Open a file for output and move the read/write control to the end of the file. 3 ios::in Open a file for reading. 4 ios::out Open a file for writing. 5 ios::trunc If the file already exists, its contents will be truncated before opening the file.
- 9. Example Example ofstream outfile; outfile.open("file.dat", ios::out | ios::trunc ); Similar way, you can open a file for reading and writing purpose as follows − fstream afile; afile. Open("file.dat", ios::out | ios::in );
- 10. 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. Syntax- void close(); Closing a File
- 11. Writing to a File 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 #include <iostream.h> #include <fstream . h> using namespace std; void main() { ofstream MyFile("file1.txt"); // Create and open a text file MyFile << "Files can be tricky, but it is fun enough!"; // Write to the file MyFile. Close(); // Close the file } Sample Code
- 12. Handling Data Files Data files in C++ can be handles in two ways 1. Sequential file handling –A sequential access is that in which the records are accessed in some sequence, i.e., the information in the file is processed in order, one record after the other. This access method is the most primitive one. 2. Random File Handling - Random-access file is a term used to describe a file or set of files that are accessed directly instead of requiring that other files be read first. A random-access data file enables you to read or write information anywhere in the file.
- 13. Sequential I/O with files • The file stream classes support a number of member functions for performing the input and output operations on files. • The functions get() and put() are capable of handling a single character at a time. • The function getline() lets you handle multiple characters at a time. •Another pair of functions read() and write() are capable of reading and writing blocks of binary data. The get(), getline() and put() Functions The functions get() and put() are byte-oriented. That is, get() will read a byte of data and put() will write a byte of data. The get() has many forms, but the most commonly used version is shown here, along with put() : istream & get(char & ch) ; //prototype of put() istream & getline(char * buf, int num, char delim = 'n') ; //prototype of getline()
- 14. Random I/O with Files The seekg(), seekp(), tellg() and tellp() Functions In C++, random access is achieved by manipulating seekg(), seekp(), tellg() and tellp() functions. The seekg() and tellg() functions allow you to set and examine the get_pointer, and the seekp() and tellp() functions perform these operations on the put_pointer. The seekg() and tellg() functions are for input streams (ifstream) and seekp() and tellp() functions are for output streams (ofstream). However, if you use them with an fstream object then tellg() and tellp() return the same value. Also seekg() and seekp() work the same way in an fstream object.