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C++ language allows us to perform important Disk input/output operations such as -

• Creating a new file on the disk.
• Reading the file stored on the disk.
• Writing data to the file stored on the disk.
• Appending new data to the end of the file stored on the disk.
• Modifying the content of the file stored on the disk.

In order to perform any file operations, C++ provides us a few file stream classes, such as -

• ifstream, to perform the file input operations.
• ofstream, to perform the file output operations.
• fstream, to perform the any file input and output operations.

How to open a file?

By using the object of any file stream class, we could call the open() function, using which we could provide location of the file stored on the disk and in return(if the file is found), the open() function opens the file in a specific mode to let you perform a specific file operation.

Let us take a look at a general syntax of open() function to open a file.

file-stream-object("filename", mode);

• file-stream-object, is object of a file stream class used to perform a specific file operation.
• filename, is the name of file on which we are going to perform file operations.
• mode, is single or multiple file modes in which we are going to open a file.

File Modes

In C++, for every file operation, exists a specific file mode. These file modes allow us to create, read, write, append or modify a file. The file modes are defined in the class ios. Let's see all these different modes in which we could open a file on disk.

File Modes	Description
ios::in"	Searches for the file and opens it in read mode only(if the file is found).
ios::out	Searches for the file and opens it in write mode. If the file is found, its content are overwritten. If file is not found, a new file is created. Allows you to write to the file.
ios::app	Searches for the file and opens it in append mode i.e. this mode allows you to append new data to the end of a file. If file is not found, a new file is created.
"ios::binary"	Searches for the file and opens the file(if the file is found) in a binary mode to perform binary input/output file operations.
ios::ate	Searches for the file, opens it and positions the pointer at the end of the file. This mode when used with ios::binary, ios::in and ios::out modes, allows you to modify the content of a file.
"ios::trunc"	Searches for the file and opens it to truncate or deletes all of its content(if the file is found.
"ios::nocreate"	Searches for the file and and if the file is not found, a new file will not be created.

This tutorial has introduced you to some important disk input/output operations that we can perform on a file and modes in which we can open a file on disk. In the next tutorial, we are going to explain how to read an existing file on the disk and what if the file we are looking for does not exist? So, see you in the next one!

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