[code lang="c#"]
FileInfo myFile = new FileInfo("c:\\myfile.txt");
if ((myFile & FileAttributes.ReadOnly) == FileAttributes.ReadOnly)
{
// remove the read only attribute
myFile.Attributes = (FileAttributes)(Convert.ToInt32(myFile.Attributes) - Convert.ToInt32(FileAttributes.ReadOnly));
}
[/code]
myFile.Attributes -= FileAttributes.ReadOnly; works as well
Comment by Scott — August 26, 2008 @ 8:24 am
awesome input, thanks Scott!
Comment by omatase — August 26, 2008 @ 10:37 am
In case someone needs the VB.NET Code:
Dim myFile As FileInfo = New FileInfo(“c:\myfile.txt”)
If myFile.IsReadOnly ThenThen
‘ remove the read only attribute
myFile.IsReadOnly = False
End If
Comment by Deniz — October 21, 2008 @ 6:33 am
For changing the flag, this is a little prettier
// flip the read only attribute
myFile.Attributes ^= FileAttributes.ReadOnly;
Comment by Mark Scott — November 7, 2008 @ 6:34 am
Scott’s solution does not consistently work. I’m not sure why exactly, but when applied repeatedly to a file it turned read-only again.
This works:
FileInfo info = new FileInfo(file);
info.Attributes &= ~FileAttributes.ReadOnly;
Comment by ripper234 — March 16, 2009 @ 4:44 am
The easiest solution is:
myFile.IsReadOnly = false;
…or, as ripper234 wrote:
myFile.Attributes &= ~FileAttributes.ReadOnly;
Neither of these methods require a pre-test as they ALWAYS remove read-only status.
————–
Scott’s solution (using the -= assignment operator) is dangerous for two reasons:
(1) It works ONLY IF the ReadOnly attribute is set, thus a test is required beforehand.
(2) It is performing a subtract operation, which is not is not the best choice when working with binary flags. The subtract operation works if condition 1 (above) is true, but additional subtract operations will ALTER OTHER BITS in the FileAttributes field!
To appropriately manipulate binary flags, you should only use bitwise (binary) operators:
& (bitwise AND) – clears bits
| (bitwise OR) – sets bits
^ (bitwise XOR) – flip-flops bits
~ (bitwise negation) – flip-flops all bits
You can also use the corresponding compound assignment counterparts:
&= (bitwise AND and assign)
|= (bitwise OR and assign)
^= (bitwise XOR and assign)
Not appropriate for flags, but appropriate for other binary operations:
<> (shift right) – moves bits to the right (same as divide by n^2, but faster)
———–
How ripper234’s method works:
FileAttributes.ReadOnly = 0×0000000000000001
In order to use the bitwise AND operator to clear a bit, we need the complement of this:
~FileAttributes.ReadOnly = 0×1111111111111110
Next, we perform the bitwise AND, then assign it back:
myFile.Attributes = myFile.Attributes & ~FileAttributes.ReadOnly;
The &= operator is shorthand for the above and yields:
myFire.Attributes &= ~FileAttributes.ReadOnly;
Comment by Kevin P. Rice — August 25, 2009 @ 12:19 am