Write code to open file contact txt with showing information and print it in following form

File I/O in C

File I/O in C is very similar to Matlab. There are two main differences. One, we have to type the FILE variable. Two, we read one value (or a single line of values) at a time, whereas by default in Matlab, you may read many values at once.

The basic steps for using a File in C are always the same:

1. Create a variable of type "FILE*".

2. Open the file using the "fopen" function and assign the "file" to the variable.

3. Check to make sure the file was successfully opened by checking to see if the variable == NULL. If it does, an error has occured.

4. Use the fprintf or fscanf functions to write/read from the file. Usually these function calls are placed in a loop. In the case of reading data, usually, the data is read in and placed in an array, but sometimes we process the data "on the fly" (i.e., we do not store the data, we process it and create a result directly before reading any more data.

Example Code

Here are examples of the basic syntax for opening a file and writing to or reading from it:

Here is a comparison between reading from a file in Matlab and in C:

C Language

Matlab

FGETS function: Read One Line at a Time

To read one line from a file (or the keyboard) at a time, use the fgets function.

fgets places the "\n" (newline) at the end of the line. Thus if we type in "hello", what really goes into the variable line is [ 'h', 'e', 'l', 'l', 'o', '\n', '\0' ]

fgets returns the keyword null on error. Thus we often use:

Python provides inbuilt functions for creating, writing, and reading files. There are two types of files that can be handled in python, normal text files and binary files (written in binary language, 0s, and 1s).

• Text files: In this type of file, Each line of text is terminated with a special character called EOL (End of Line), which is the new line character (‘\n’) in python by default.
• Binary files: In this type of file, there is no terminator for a line, and the data is stored after converting it into machine-understandable binary language.

In this article, we will be focusing on opening, closing, reading, and writing data in a text file.

File Access Modes

Access modes govern the type of operations possible in the opened file. It refers to how the file will be used once its opened. These modes also define the location of the File Handle in the file. File handle is like a cursor, which defines from where the data has to be read or written in the file. There are 6 access modes in python.

1. Read Only (‘r’) : Open text file for reading. The handle is positioned at the beginning of the file. If the file does not exists, raises the I/O error. This is also the default mode in which a file is opened.
2. Read and Write (‘r+’): Open the file for reading and writing. The handle is positioned at the beginning of the file. Raises I/O error if the file does not exist.
3. Write Only (‘w’) : Open the file for writing. For the existing files, the data is truncated and over-written. The handle is positioned at the beginning of the file. Creates the file if the file does not exist.
4. Write and Read (‘w+’) : Open the file for reading and writing. For an existing file, data is truncated and over-written. The handle is positioned at the beginning of the file.
5. Append Only (‘a’): Open the file for writing. The file is created if it does not exist. The handle is positioned at the end of the file. The data being written will be inserted at the end, after the existing data.
6. Append and Read (‘a+’) : Open the file for reading and writing. The file is created if it does not exist. The handle is positioned at the end of the file. The data being written will be inserted at the end, after the existing data.

How Files are Loaded into Primary Memory

There are two kinds of memory in a computer i.e. Primary and Secondary memory every file that you saved or anyone saved is on secondary memory cause any data in primary memory is deleted when the computer is powered off. So when you need to change any text file or just to work with them in python you need to load that file into primary memory. Python interacts with files loaded in primary memory or main memory through “file handlers” ( This is how your operating system gives access to python to interact with the file you opened by searching the file in its memory if found it returns a file handler and then you can work with the file ).

Opening a File

It is done using the open() function. No module is required to be imported for this function.

The file should exist in the same directory as the python program file else, the full address of the file should be written in place of the filename. Note: The r is placed before the filename to prevent the characters in the filename string to be treated as special characters. For example, if there is \temp in the file address, then \t is treated as the tab character, and an error is raised of invalid address. The r makes the string raw, that is, it tells that the string is without any special characters. The r can be ignored if the file is in the same directory and the address is not being placed. 

Python

file1 = open("MyFile.txt","a")

file2 = open(r"D:\Text\MyFile2.txt","w+")

Here, file1 is created as an object for MyFile1 and file2 as object for MyFile2

Closing a file

close() function closes the file and frees the memory space acquired by that file. It is used at the time when the file is no longer needed or if it is to be opened in a different file mode. File_object.close() 

Python

file1 = open("MyFile.txt","a")

file1.close()

Writing to a file

There are two ways to write in a file.

1. write() : Inserts the string str1 in a single line in the text file.

1. writelines() : For a list of string elements, each string is inserted in the text file.Used to insert multiple strings at a single time.

Reading from a file

There are three ways to read data from a text file.

1. read() : Returns the read bytes in form of a string. Reads n bytes, if no n specified, reads the entire file.

1. readline() : Reads a line of the file and returns in form of a string.For specified n, reads at most n bytes. However, does not reads more than one line, even if n exceeds the length of the line.

1. readlines() : Reads all the lines and return them as each line a string element in a list.

Note: ‘\n’ is treated as a special character of two bytes 

Python3

file1 = open("myfile.txt","w")

L = ["This is Delhi \n","This is Paris \n","This is London \n"] 

file1.write("Hello \n")

file1.writelines(L)

file1.close()

file1 = open("myfile.txt","r+") 

print("Output of Read function is ")

print(file1.read())

print()

file1.seek(0) 

print( "Output of Readline function is ")

print(file1.readline()) 

print()

file1.seek(0)

print("Output of Read(9) function is ") 

print(file1.read(9))

print()

file1.seek(0)

print("Output of Readline(9) function is ") 

print(file1.readline(9))

file1.seek(0)

print("Output of Readlines function is ") 

print(file1.readlines()) 

print()

file1.close()

Output:

Appending to a file

Python3

file1 = open("myfile.txt","w")

L = ["This is Delhi \n","This is Paris \n","This is London \n"] 

file1.writelines(L)

file1.close()

file1 = open("myfile.txt","a")

file1.write("Today \n")

file1.close()

file1 = open("myfile.txt","r")

print("Output of Readlines after appending") 

print(file1.readlines())

print()

file1.close()

file1 = open("myfile.txt","w")

file1.write("Tomorrow \n")

file1.close()

file1 = open("myfile.txt","r")

print("Output of Readlines after writing") 

print(file1.readlines())

print()

file1.close()

Output:

Related Article: File Objects in Python 

This article is contributed by Harshit Agrawal. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to . See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

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