life after Windows....

"Mxsmanic" wrote in message
...
Keith Willshaw writes:

It looks in the registry oh dim one

How will the registry tell the OS the purpose of a file being created by
an
application?

Typical entry

HKEY_CLASSES_ROOT\.docx
Key Name Value
Default Word.Document.12
Content Type
application/vnd.openxmlformats-officedocument.wordprocessingml.document


What about operating systems with no registry?


They typically have similar mechanisms, thats how they know to open
Word if you double click on a .doc file


No wonder you couldnt hold down a job in IT

Keith

Keith Willshaw writes:

Typical entry

HKEY_CLASSES_ROOT\.docx
Key Name Value
Default Word.Document.12
Content Type
application/vnd.openxmlformats-officedocument.wordprocessingml.document

So?

The program calls the API with a request to create file c:\data\xyz.abc. How
does the OS determine the purpose of this file, and how does it know whether
or not the file is being created in the "right" place?

"Mxsmanic" wrote in message
...
Keith Willshaw writes:

Typical entry

HKEY_CLASSES_ROOT\.docx
Key Name Value
Default Word.Document.12
Content Type
application/vnd.openxmlformats-officedocument.wordprocessingml.document

So?

The program calls the API with a request to create file c:\data\xyz.abc.
How
does the OS determine the purpose of this file, and how does it know
whether
or not the file is being created in the "right" place?


The OS neither knows nor cares, all that matters is that the action
is legal. That is to say the file name is of the right format for the
OS and that the location being accessed 1) exists and 2) the calling
procedure has the correct access rights.

The base tier of the calling program on the other hand should have rules
implemented
that ensure that the correct extension is appended to the file and that the
correct write opertation is carried out, sequential , text , binary etc.

If the file location is critical then the rules that govern that should be
implemented
in the middle tier. If that decision requires human intervention this is
passed to
the top or presentation tier.

This is software design 101 by the way.

Keith

Keith Willshaw writes:

The OS neither knows nor cares, all that matters is that the action
is legal.

Right. Which makes it possible for applications to misuse even the best APIs.
QED.

"Mxsmanic" wrote in message
...
Keith Willshaw writes:

The OS neither knows nor cares, all that matters is that the action
is legal.

Right. Which makes it possible for applications to misuse even the best
APIs.
QED.


The question you put was

If a program creates a file, how does the API check to see that the file's
name is correct?

Now API's are NOT only implemented at the OS level but I dont expect a
tour guide to know that. In the context of the OS API the posit that the
name
is 'correct' simply means legal etc.

As an example the Windows WriteFile Api takes the following arguments

BOOL WriteFile(
HANDLE hFile, // handle to file to write to
LPCVOID lpBuffer, // pointer to data to write to file
DWORD nNumberOfBytesToWrite, // number of bytes to write
LPDWORD lpNumberOfBytesWritten, // pointer to number of bytes written
LPOVERLAPPED lpOverlapped // pointer to structure needed for overlapped
I/O
);It returns False if the operation fails , because of an illegal name for
example.
The details of the error may be retrieved by a GetLastError call.

On the other hand the API's I call at the application level have much
more specific error checking. If I attempt to open a jpeg filewith an API
it reads the file header to check its a valid format.

Keith