Console.WriteLine Exception File File.ReadAllText

`File.Copy`

Many ways exist to copy a file. Some are more efficient than others. With File.Copy in VB.NET we issue an instruction to the operating system.

When we access the operating system with functions like File.Copy, exceptions are sometimes thrown. We explore the File.Copy subroutine in VB.NET.

Example

Here we call File.Copy—the file specified must be found in the program's directory. If it is not found, an exception will be thrown. The file must exist for the copy to succeed.

Then After the File.Copy sub returns, we call File.ReadAllText on the original and copied files.

Finally We display the contents of both files to show that the destination file has the same contents as the original.

Imports System.IO

Module Module1

    Sub Main()
        ' Copy one file to a new location.
        File.Copy("file-a.txt", "file-b.txt")

        ' Display file contents.
        Console.WriteLine(File.ReadAllText("file-a.txt"))
        Console.WriteLine(File.ReadAllText("file-b.txt"))
    End Sub

End ModuleHow are you today?
How are you today?

Overwrite

For File.Copy to succeed, the destination file must not exist. You can override this behavior by passing True as the third argument.

And This eliminates the "already exists" exception. The previous contents of the destination file are lost.

Imports System.IO

Module Module1

    Sub Main()
        ' Allow the destination to be overwritten.
        File.Copy("file-a.txt", "file-b.txt", True)

        ' Display.
        Console.WriteLine(File.ReadAllText("file-a.txt"))
        Console.WriteLine(File.ReadAllText("file-b.txt"))
    End Sub

End ModuleI am well, thank you.
I am well, thank you.

A discussion

A file can be copied by loading it into memory (like with File.ReadAllText), and then writing that data to a new file. But this involves more than an operating system call.

However We may need to do further processing on the file. In this case it may be more efficient to just write the in-memory version to the disk.

Tip Using File.Copy is usually the better choice, but this is not always true. Sometimes it can be avoided.

With File.Copy the original file must exist. And the destination file must not exist, unless you specify overwriting. It may cause exceptions—using try and catch is worthwhile.