Programming Excel with VBA and .NET

Read and Write Files

There are a number of different ways to read and write files in Visual Basic, and which you choose depends on what you are trying to do, as described in Table 3-13.

Table 3-13. File-access techniques in Excel Visual Basic

Technique	Use to	Look here
Intrinsic functions	Read or write simple datafiles	This section
FileSystemObject	Create files, folders, and control file attributes	Chapter 6
Workbooks, Workbook objects	Create, open, and save Excel workbook files; import datafiles into workbooks	Chapter 8
XMLMap object	Import or export XML datafiles from a workbook	Chapter 15

In short, you shouldn’t assume the Visual Basic intrinsic functions are the best way to read and write files in all situations. Actually, I prefer the FileSystemObject for most general file-access tasks, but it’s important to be thorough, so I’ll cover the intrinsic file-access functions here (Table 3-14).

Table 3-14. Visual Basic’s intrinsic file-access functions

Category	Function	Use to
Access	Close	Close an open file
	FileCopy	Copy a file
	FreeFile	Get a file number for Open
	Lock...Unlock	Prevent others from accessing all or part of a file
	LOF	Get the length of an open file in bytes
	Open	Open a file
	Reset	Close all open files
Attributes	FileAttr	Get the attributes of an open file
	FileDateTime	Get the date that a file was created or changed
	FileLen	Get the length of a file ...