|
I'm trying to load an image into a byte array. The following code seems to be OK for the moment but i'm worried that it's not right.
FileStream fs = new FileStream(FileName,FileMode.Open);<br />
byte [] ImageData = new byte[fs.Length];<br />
fs.Read(ImageData,0,(int)fs.Length);
Firstly, while i can't see anyone loading files bigger than int.MaxValue any time soon, it's always nice to future proof your code and someone might load a video that big, even today. For the application I'm using it for I'll probably block files over about 10 Meg anyway so I can ignore this issue.(I might stick in a LATER: comment and come back to it)
Second and of more immediate concern is that I read somewhere (but have now lost the link) that fs.Read will block until it has some data, not necessarily all the data in the stream.
Is my simple code OK or should I be checking whether the stream is fully loaded before i do things with the data? It seems to work allright at the moment but this is a reasonably fast machine with good disks and not much swap file use.
Russell
|
|
|
|
|
Looks fine to me. You want the image file, in it's encoded format, right ?
Christian Graus - C++ MVP
'Why don't we jump on a fad that hasn't already been widely discredited ?' - Dilbert
|
|
|
|
|
I'm putting the file into a DB so as long as it's a valid byte array I hope it'll be OK when i get it back out again.
Was just a bit worried that the webpage i read yesterday used about 20 klines of code to achieve the same result.
Thanks for your swift reply
Russell
|
|
|
|
|
The Read method returns an integer that contains the number of bytes read. You should check this value to be sure that all the data was read.
From the documentation on the Read method in MSDN:
"The Read method returns zero only after reaching the end of the stream. Otherwise, Read always reads at least one byte from the stream before returning. If no data is available from the stream upon a call to Read, the method will block until at least one byte of data can be returned. An implementation is free to return fewer bytes than requested even if the end of the stream has not been reached."
If you are using framework 2, you can use the File.ReadAllBytes method.
---
Year happy = new Year(2007);
|
|
|
|
|
I think you are right about fs.Read blocking for at least some data
The doc says "Returns the total number of bytes read into the buffer. This might be less than
the number of bytes requested if that number of bytes are not currently available, or zero if
the end of the stream is reached."
So returning zero because nothing is available yet seems not to occur, hence a wait for data.
Whether you can go on with partial data is entirely up to you (do you need all data, or
just enough to figure out the image size, a thumbnail, ...). You may have to take
the return value of fs.Read into account.
If you need to be sure all data is available, but dont want to wait for it, consider
working asynchronously (with BeginRead).
Luc Pattyn
|
|
|
|
|
Looks like readallbytes is about to become my friend, thanks for that I hadn't noticed it before.
Russell
|
|
|
|
|
Documentation promises an UnauthorizedAccessException for a read-only file 
Luc Pattyn
|
|
|
|
|
Read only file is only one of the causes of that error.
The process might not have permissions to read the file for instance.
Russell
|
|
|
|
|
Sure, I am just saying
1) I dont understand why Read should fail on read-only files
2) you may have to read a read-only image file, for which File.ReadAllBytes would fail
Luc Pattyn
|
|
|
|
|
So I tried it on a read-only file, and it works.
I'm still puzzled why the doc mentions read-only as a possible cause for
UnAuthorizedAccessException.
It does not mention it for File.OpenText, OK
it does for File.OpenWrite, OK
it should not for File.ReadWhatsoever !
Luc Pattyn
|
|
|
|
|
I assume that the doc has been created by an automated process and 1 has been ammended later and the other not. The inconsistency with the other methods is bizarre but not unusual for MS.
Russell
|
|
|
|
|
Hi,
I need to transfer some data from one table to another in SQL Server 2000.
Here's the scenario:
Table 1 (Source): Name, Col1, Col2, Col3, Col4
Table 2 (Destination): Name, Cols
I want Cols to store the consolidated values of Col1 Col2 Col3 and Col4,
separated by 1 comma and a space, i.e. ,<space>
For example, if in Table 1, Col1 = 'Me' Col2='Myself' Col3='and' Col4='Irene'
Then in the Destination Table 2, Cols should be equal to 'Me, Myself, and, Irene'
This one is a real cracker. Will anyone be able work out a query or something?
If no one here can, I guess I can't go anywhere else.
Thanks.
ASP - AJAX is SEXY. PERIOD.
|
|
|
|
|
I do that into Microsoft Access 2000
I think it's work into SQL SERVER 2000
INSERT INTO Table2 ( name, cols )
SELECT Table1.name, [col1]+', '+[col2]+', '+[col3]+', '+[col4] AS Expr1
FROM Table1;
I hope that help you ...
|
|
|
|
|
Leaving aside my worries about DB normalisation as i assume this is being done for performance reasons.
INSERT INTO Table2 ( [name], cols )
SELECT Table1.[name], col1 & ", " & col2 & ", " & col3
FROM Table1
HTH
Russ
|
|
|
|
|
Thanks to both of you! Both methods work like a charm!!!!!
Yaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa! Now I can uninstall
that stupid Toad util. 
ASP - AJAX is SEXY. PERIOD.
|
|
|
|
|
Hello!
Ive got a Method1 with a try-catch. In Method1 I call Method2 which also has a try-catch. When exception is thrown in Method2, and the catch sequence is run, I want the application to end the current operation(not end the whole application, just what the user tried doing last). Instead the application keeps going in Method1 (where another exception soon will be thrown since Method2 wasn't run correctly). What is the best way of doing this?
/regards
|
|
|
|
|
You could rethrow the exception catched in Method2 or throw a new exception (preferrably using the catched one as inner exception), so Method1 is noticed something has gone wrong in Method2 and its try-catch gets immediatly entered.
"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning." - Rick Cook www.troschuetz.de
|
|
|
|
|
Use the finally clause after the catch
|
|
|
|
|
|
welcome
|
|
|
|
|
i would return a success state from method2. If the exception that you caught in method2 could reasonably be described as expected (file does not exist, server not available etc) then i would not rethrow the error. If , however, the error is unexpected I would rethrow the Error adding the original error as the inner exception of the new exception object.
Let's say string method2 () is a load file method
If the user cancels the dialog or the file is not a text file and can't be read then instead of returning a string containing the text from the file i return a null. Method1 sees a null and exits without carrying out further work. If while trying to open the file an unrecoverable error occurs let's say a "Your Harddisk has borked" Error then I create and throw an exception and let the main app deal with it.
I'm a great believer in only throwing errors as a last resort and trying to not use them in the expected flow of an application.
Russell
|
|
|
|
|
If you catch the exception in Method2 and pretend that nothing is wrong, Method1 will be unaware of the error condition.
Re-throw the exception or throw a new exception in Method2, and handle that in the catch in Method1.
Alternatively (but this is sometimes frowned upon in object orientation) you can return a status from Method2 that tells Method1 if it succeeded or not.
---
Year happy = new Year(2007);
|
|
|
|
|
Hi All,
I am using a c#.NET windows application,
is there any explicit method for comparing two folders according to their size and date modified?
Send Me any Related Link.Please it's Urgent
thanks
Tirumal
|
|
|
|
|
AFAIK the only way is to compare folder contents, a file at a time.
Luc Pattyn
|
|
|
|
|
tirumal1231 wrote: .Please it's Urgent
It seems that it always is.
Christian Graus - C++ MVP
'Why don't we jump on a fad that hasn't already been widely discredited ?' - Dilbert
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
