Question

I’m writing a C# app to read a file that another application holds open. As some of you may guess, all I get is IOExceptions because “the file is being used by another process”. I’ve tried tweaking File.Open() a little; this is my current try:

FileStream fsIn = File.Open(fileName, FileMode.Open, FileAccess.Read, FileShare.Read);

(I know that the FileShare flag is more meaningful for other processes that will access the file thereafter, but I have tried with it anyway.)

What puzzles me is that Notepad.exe will open the file just fine. Before I dig into Filemon for more clues, does any of you know how to open the file the way Notepad does? Thanks.

Answer 1

You almost have it. You actually want FileShare.ReadWrite:

FileStream fsIn = File.Open(fileName,
                            FileMode.Open,
                            FileAccess.Read,
                            FileShare.ReadWrite);

FileShare.Read disallows other processes from writing to that file. FileShare.ReadWrite allows this.

Write Allows subsequent opening of
the file for writing. If this flag is
not specified, any request to open the
file for writing (by this process or
another process) will fail until the
file is closed. However, even if this
flag is specified, additional
permissions might still be needed to
access the file.

ReadWrite Allows
subsequent opening of the file for
reading or writing. If this flag is
not specified, any request to open the
file for reading or writing (by this
process or another process) will fail
until the file is closed. However,
even if this flag is specified,
additional permissions might still be
needed to access the file.

It’s backwards to me as well.