Re: Huh? Can this be logical? - C# Discussion Boards

31-Aug-04 6:24

Looking for some answers on MSDN I ran across the following code.

If (null != email)

Is that legal in C#, and even if it does compile, is it logical?

Shouldn't it more likely read:

If (email != null)

Best,
Jerry

Contrary to the cliche, genuinely nice guys most often finish first or very near it.--Malcolm Forbes

Steven Campbell31-Aug-04 6:32

Steven Campbell

31-Aug-04 6:32

This is a wierd convention that older C programmers follow. It is perfectly legal.

The reason that it is done, is that in C, it is legal to say if (email = null), (note the single equal sign) and it will always evaluate to true. So, to prevent possible errors caused by mistypes, C programmers switch the arguments, i.e. if (null = email). This second version is not legal syntax, and will give a compiler error. The programmer can then fix it by changing it to if (null == email).

This is not necessary in C# (but neither is it illegal), because the C# compiler will complain at if (email = null).

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leppie31-Aug-04 6:38

leppie

31-Aug-04 6:38

Steven Campbell wrote:
if (email = null), (note the single equal sign) and it will always evaluate to true.

allways be false i think u mean :p

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Christian Graus31-Aug-04 11:05

31-Aug-04 11:05

I'd expect it to be true, because the assignment would not fail.

Christian

I have drunk the cool-aid and found it wan and bitter. - Chris Maunder

Heath Stewart31-Aug-04 11:58

31-Aug-04 11:58

The condition isn't checking the assignment, it would check the resultant expression. In ths case, that'd be email. The code breaks apart like so:

email = null;
if (email)
{
  // ...
}

In C#, however, the above expression isn't valid like it would be in C/C++ (where NULL is defined as 0). You would get an error in this case, but not because you'd be using an assignment operator instead of an equivalence operator.

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Christian Graus31-Aug-04 12:17

31-Aug-04 12:17

Oh, OK. Obviously I had not tried it.

Heath Stewart wrote:
Software Design Engineer
Developer Division Sustained Engineering
Microsoft

Cool. Do you know anything about DX9, specifically the AudioVideoPlayback namespace ? Was it released by mistake ? I've had a lot of fun figuring out it's many flaws.....

Christian

I have drunk the cool-aid and found it wan and bitter. - Chris Maunder

Heath Stewart31-Aug-04 12:23

31-Aug-04 12:23

I've worked with DX9 a little, but I admit I don't know a whole lot about it (mostly from a graphics manipulation regard, not API use).

I recommend reading Managed DirectX 9 Kick Start : Graphics and Game Programming[^]. It's a very good book and you'd probably have a better time with it. Like I said, I understand all the API stuff, but matrices - when it comes to graphics - always seem to elude me. I will say, however, that you're articles have helped clear a few things up.

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Software Design Engineer
Developer Division Sustained Engineering
Microsoft

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Christian Graus1-Sep-04 10:51

1-Sep-04 10:51

Heath Stewart wrote:
I recommend reading Managed DirectX 9 Kick Start : Graphics and Game Programming[^].

I have it. I assume the rest of the book is better, the bit on audio video playback is 3 pages which glosses over the API, tells me that Microsoft does not regard it as a full implimentation, and it's not going to be updated. It doesn't cover any of the bugs in the API, I presume the author has never actually used this part of DirectX9, and felt they needed to cover it, so they skimmed the docs.

I'm writing an article on all the ways that the AudioVideoPlayback namespace fails to perform as expected, and a wrapper class that will make it a little bit close to usable. I've built an entire project around DX9, and I'm kind of wishing I hadn't.

Christian

I have drunk the cool-aid and found it wan and bitter. - Chris Maunder

Jerry Hammond31-Aug-04 11:45

31-Aug-04 11:45

Steven Campbell wrote:
The programmer can then fix it by changing it to if (null == email).

Ok, but how can

null

be "equal to" anything? This has got to be a concept I'm not able to fathom or I am just unfamiliar with it. And, for now, it just seem logical.

Best,
Jerry

Contrary to the cliche, genuinely nice guys most often finish first or very near it.--Malcolm Forbes

Heath Stewart31-Aug-04 11:52

31-Aug-04 11:52

Any reference object - like email (presumably a string, which is a reference type) - is null if it doesn't reference an object. So, it's "value" is null.

string email = null;
null == email; // Returns true
email = "you@codeproject.com";
null == email; // Returns false, references the string "you@codeproject.com

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Developer Division Sustained Engineering
Microsoft

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Christian Graus31-Aug-04 12:19

31-Aug-04 12:19

if 2+2 = 4, then 4 = 2+2. The concept is the same. The two values are checked for equality, that the constant value is on the left makes no difference to the compiler, and in C++ was a good was to avoid a bug that can be a nightmare to find. I know, I still sometimes write code like this, a habit I formed in my C++ days.

Christian

I have drunk the cool-aid and found it wan and bitter. - Chris Maunder

Jerry Hammond31-Aug-04 14:18

31-Aug-04 14:18

Ok, thanks Heath and Christian. I think I understand what's going on with that now.

Best,
while(null==jerry)
{
null++;
return;
}

Contrary to the cliche, genuinely nice guys most often finish first or very near it.--Malcolm Forbes

Heath Stewart31-Aug-04 6:44

31-Aug-04 6:44

To expand on what Steven said, the two are the same because it's a simple comparison. The IL generated from about would be:

ldnull
ldfld email
beq Equal // If the two are equal skip the if block
// if block runs here
Equal:
// After the if block

It doesn't matter if you load null or the field (or variable, whichever) first, you're still comparing the value of two objects.

This posting is provided "AS IS" with no warranties, and confers no rights.

Software Design Engineer
Developer Division Sustained Engineering
Microsoft

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Jerry Hammond31-Aug-04 6:52

31-Aug-04 6:52

Thanks for the answers all. Would this also hold true for the is-equal-to '==' also?

Best,
Jerry

Contrary to the cliche, genuinely nice guys most often finish first or very near it.--Malcolm Forbes

Jerry Hammond31-Aug-04 8:43

31-Aug-04 8:43

OMG! I just woke up and realized what a stupid question that was.

That's what I get for watching the grandchildren and coding at the same time...

Best,
Jerry

Contrary to the cliche, genuinely nice guys most often finish first or very near it.--Malcolm Forbes

Eric Gunnerson (msft)1-Sep-04 12:45

Eric Gunnerson (msft)

1-Sep-04 12:45

In C++, it's possible to write:

if (x = 0)

when you mean to write

if (x == 0)

Because of that, some developers invert the order of what they write, as:

if (0 = x)

is illegal, while

if (0 == x)

is legal.

This is not a problem in C#, where if (x = 0) is prohibited.

Logging asynchronously

Michel Rainville31-Aug-04 6:22

Michel Rainville

31-Aug-04 6:22

Hi
I need a logging framework that let me log asynchronously.

Do you have any suggestion ?

I tried to figure out if log4net does all the logging asynchronously. Does it depend on a specific Appender or all logging is done asynchronously ?

I did a test in which I log 1500 time the same string.
- Log4net with FileAppender is doing it in approx. between 100 and 200 miliseconds;
- Log4net with BufferingForwardingAppender combine with FileAppender is doing it in approx. 2000 miliseconds;
- System.IO does it in approx. 10 miliseconds.

I also tried with EIF using my own EventSink sending all request in a MSMQ queue but using EIF is not as easy to deploy as log4net so...

Any suggestion would be appreciate

Heath Stewart31-Aug-04 6:55

31-Aug-04 6:55

The EIF offers more than just logging using the EIF.

What you're logging to, however, greatly matters unless you're queuing requests in order and flushing them to disk or some other sequential data store.

Note that a simple solution is to define a delgate on the logging method and execute that asynchronously. The backing store matters, however, because doing things this way with a non-thread-safe backing store could cause major problems.

For example:

internal delegate void Log(string message, string category);
// ...
Log log = new Log(Trace.WriteLine);
log.BeginInvoke(message, category, null, null);

It's an overly simplified example, but hopefully gives you the idea.

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Software Design Engineer
Developer Division Sustained Engineering
Microsoft

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Daniel3000i31-Aug-04 8:00

Daniel3000i

31-Aug-04 8:00

Log4Net looks suspiciously like Log4J. Easy to use; but a hog and will slow your program down. In Log4J there are asynchronous appenders, look for the same in Log4Net. You should see some increase in speed; but I wouldn't expect any logging framework to be faster or even as fast as System.IO.

Daniel

Michel Rainville31-Aug-04 10:08

Michel Rainville

31-Aug-04 10:08

Thanks for your reply Daniel

I have a couple of question regarding what you just said:

1- Can you tell what are the appender that you know is asynchronous (in Log4J at least)
2- Why would you expect System.IO to be faster ? I understand that there is a cost (overhead) to use this kind of framework but if the appender is sending message (logging event) to a structure that it is store in memory, I expect it to be faster than an IO on disk. Am I wrong Daniel.

If I recall my first post, this is exactly what I did using EIF and a specific EventSink (appender). My EventSynk only take the logging event and put it on an MSMQ and return very fast (but telling that remind me that I did not save the metrics for that one, so how fast it realy is... I'll tell you)

Anyway, Thank you to both of you who reply to this post.

I can't believe that in 2004 I'm still worry about logging

Thanks again
Michel