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Join Date: Feb 2005
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As seen in another thread, I'm working on a Log class. I'm running into an issue that if I delete the file that's being written to, the Log class doesn't detect it and continues to 'think' it's writing even though the file is gone... (Note that this is on sun solaris in case it matters)
I've tried the following to try and detect this
(assuming my ofstream is named out)
!out.is_open()
!out.good()
out.fail()
None of them seem to detect this issue. (Nor changing the permissions to non-write while the file has already been opened by the app). Note that these functions DO catch a problem with opening the file, but not when it's already opened. Any advice?
I've tried the following to try and detect this
(assuming my ofstream is named out)
!out.is_open()
!out.good()
out.fail()
None of them seem to detect this issue. (Nor changing the permissions to non-write while the file has already been opened by the app). Note that these functions DO catch a problem with opening the file, but not when it's already opened. Any advice?
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Join Date: Aug 2003
Location: Austin, TX
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Originally Posted by winbatch
As seen in another thread, I'm working on a Log class. I'm running into an issue that if I delete the file that's being written to, the Log class doesn't detect it and continues to 'think' it's writing even though the file is gone... (Note that this is on sun solaris in case it matters)
I've tried the following to try and detect this
(assuming my ofstream is named out)
!out.is_open()
!out.good()
out.fail()
None of them seem to detect this issue. (Nor changing the permissions to non-write while the file has already been opened by the app). Note that these functions DO catch a problem with opening the file, but not when it's already opened. Any advice?
Why not close the file descriptor?
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Join Date: Feb 2005
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Not sure I follow. I have a program that is writing/appending to a file every second (as a test). In another window/session, I'm deleting that file via the rm command in unix. I want my program to detect that it can no longer write to the file. instead, it just keeps on writing. (Though nothing is actually written as the file is gone)
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Join Date: Aug 2003
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Originally Posted by winbatch
Not sure I follow. I have a program that is writing/appending to a file every second (as a test). In another window/session, I'm deleting that file via the rm command in unix. I want my program to detect that it can no longer write to the file. instead, it just keeps on writing. (Though nothing is actually written as the file is gone)
So, in *nix, when you open a file descriptor, you grab a reference to that file. Thus, when you unlink(2) that file using the "rm" command, you're only dropping that reference. Because you have a stream open (and another reference), the file will not actually be removed [yet]. Once you close the stream, you will release that reference, and presumably at that point the file's reference count will then drop to 0 and be "removed".
Ah reference counting, fun for the entire family.
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What you want to do is not possible in standard C++. You seem to think that a file stream knows if the external device is available if you remove it between construction and destruction of the stream. In reality, all you're doing is invoking undefined behavior by writing to a device that you've told the stream exists and will continue to exist until destruction. That's an implied contract when you open a file stream and you're not adhering to it.
My kneejerk reaction to this problem is to tell you not to delete the file until you're done with it. However, you can do a platform dependent test to see if the file exists before every operation on it. However, that's inefficient and just sweeps the dirt under the rug.
My kneejerk reaction to this problem is to tell you not to delete the file until you're done with it. However, you can do a platform dependent test to see if the file exists before every operation on it. However, that's inefficient and just sweeps the dirt under the rug.
I'm a programmer. My attitude starts with arrogance, holds steady at condescension, and ends with hostility. Get used to it.
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I was only deleting it to see if my class would detect it. So what you're saying is that it can't detect the deletion, or a change in permissions, etc. What about running out of disk space?
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Originally Posted by winbatch
I was only deleting it to see if my class would detect it. So what you're saying is that it can't detect the deletion, or a change in permissions, etc. What about running out of disk space?
So, if you're writing a program that's specific to a "unix" system why not use C and OS libraries?? And, like I told you, your concept and understanding of "deletion" is wrong. You can't detect deletion because nothing is BEING deleted.
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I'm not using C because my Log class uses inheritance to either be a screen, or a file (and eventually a socket, or a database, etc..)
By the way, if not for detecting problems writing, what's the point of the .bad() and .fail() functions? When would they be used?
By the way, if not for detecting problems writing, what's the point of the .bad() and .fail() functions? When would they be used?
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>So what you're saying is that it can't detect the deletion, or a change in permissions, etc
Did I studder?
>What about running out of disk space
That will cause failbit (and possibly badbit) to be set.
>By the way, if not for detecting problems writing, what's the point of the .bad() and .fail() functions?
You're confusing errors during legitimate use with blatant and intentional breaking of the rules.
Did I studder?
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Originally Posted by Narue
What you want to do is not possible in standard C++.
That will cause failbit (and possibly badbit) to be set.
>By the way, if not for detecting problems writing, what's the point of the .bad() and .fail() functions?
You're confusing errors during legitimate use with blatant and intentional breaking of the rules.
I'm a programmer. My attitude starts with arrogance, holds steady at condescension, and ends with hostility. Get used to it.
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