When a program runs, the data is in the memory but when it ends or the computer shuts down, it gets lost. To keep data permanently, we need to write it in a file.
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File is used to store data. In this topic, you will learn about reading data from a file and writing data to the file.
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fstream is another C++ standard library like iostream and is used to read and write on files.
These are the data types used for file handling from the fstream library:
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| Data type | Description |
|---|---|
| ofstream | It is used to create files and write on files. |
| ifstream | It is used to read from files. |
| fstream | It can perform the function of both ofstream and ifstream which means it can create files, write on files, and read from files. |
Opening a file
We need to tell the computer the purpose of opening our file. For e.g.- to write on the file, to read from the file, etc. These are the different modes in which we can open a file.
| Mode | Description |
|---|---|
| ios::app | opens a text file for appending. (appending means to add text at the end). |
| ios::ate | opens a file for output and move the read/write control to the end of the file. |
| ios::in | opens a text file for reading. |
| ios::out | opens a text file for writing. |
| ios::trunc | truncates the content before opening a file, if file exists. |
Let's look at the syntax of opening a file.
We have opened the file 'example.txt' to write on it. 'example.txt' file must be created in your working directory. We can also open the file for both reading and writing purposes. Let's see how to do this:
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Closing a file
C++ automatically close and release all the allocated memory. But a programmer should always close all the opened files. Let's see how to close it.
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Reading and writing on a file
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We use << and >> to write and read from a file respectively. Let's see an example.