How to Efficiently Rewind a File Pointer in Go?

Proper File Pointer Rewinding in Go

In Go, reading a file can be done using a scanner or a reader. A common scenario is to read a file using a scanner and then rewind the file pointer to read the file again using a reader. However, the recommended way to rewind the file pointer is through the Seek() method.

The Seek() method takes two arguments: the offset and the starting position. To rewind the file pointer to the beginning of the file, the following code snippet can be used:

data.Seek(0, io.SeekStart)

It is often faster to rewind the file pointer using the Seek() method than to close and reopen the file. However, if small parts of the file need to be read many times alternatively, opening the file twice might be more efficient to avoid repeated seeking.

Regarding the use of File as an io.Reader, os.File implements io.Reader, so it can be used as an io.Reader. Additionally, os.File provides additional methods specific to files, so using os.File directly is generally preferred over using bufio.NewReader() orioutil.NewReader().

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