Why Does Reading from a Go *os.File Pointer After Writing Result in Unexpected EOF?

Reading from a File After Writing with the Same *os.File Pointer in Go

In Go, it is possible to create, write, and read files using the *os.File pointer. However, reading data from the same file pointer after writing to it can result in unexpected behavior.

Problem:

Consider the following code snippet:

In this code, we create a file and write 10 lines to it using the fmt.Fprintf function. Afterward, we attempt to read 10 lines from the same file pointer using a bufio.NewReader. However, the code always prints "Done," indicating that the end-of-file was reached.

Solution:

The issue arises because when data is written to an *os.File, the file pointer is moved to the end of the file. Consequently, when we try to read from the file, we start at the end of the file and immediately encounter the end-of-file indicator.

To resolve this issue, we need to reset the file pointer to the beginning of the file before attempting to read from it. This can be achieved using the Seek function:

By adding this line after writing to the file, we ensure that the file pointer is at the beginning of the file when we start reading, allowing us to successfully read the written data.

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