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I haven't looked at the IL, but I'm pretty sure you're creating and dumping a new integer every interation in your first example. And therefore, yes, it performs worse.
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I see...
Is it the same for reference types?
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Hi,
please read my other reply first.
if it is:
string x="aha";
for (...) {
string y=x;
}
then again it wont make a difference, since y=x simply copies a reference,
it does not create an object; it has the same cost as int y=x;
And again, if the compiler notices x can not change during the loop, it
should and would move the statement outside the loop.
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Exactly the answer I was looking for! 
Thanks!
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Hi,
you should not believe everything they tell you.
int is a value type, it probably gets "allocated" on stack (meaning the stack pointer
gets lowered a bit more when you enter this method to reserve a spot for it),
this has zero cost.
(the probably means, maybe the int variable does not need storage, the JIT might
decide to keep it in one of the CPU registers, but I am not relying on this)
Anyway, there is no "new", no object, and no garbage collection involved.
both code snippets could and should result in exactly the same MSIL code;
and I would be very surprised if you can measure the slightest difference in
execution time (which would hint a compiler inefficiency, not an inherent difference
between both code snippets).
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I stand corrected, both of these...
public void Inside() {
for (int i = 0; i < 1000; i++) {
int x = i;
}
}
public void Outside() {
int x;
for (int i = 0; i < 1000; i++) {
x = i;
}
}
decompile to something similar to this...
public void Outside() {
int num1;
int num2;
for (num2 = 0; (num2 < 1000); num2 = (num2 + 1)) {
num1 = num2;
}
}
The compiler does you the favor of moving your variable outside the loop where it belongs.
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Time it through the PerformanceCounter class for large iterations in the for loop and compare results...
"Real programmers just throw a bunch of 1s and 0s at the computer to see what sticks" - Pete O'Hanlon
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For what its worth, I just ran a test and got the following results. It looks like it doesn't matter for something this small.
Inside the loop took 552645639 ticks.
Outside the loop took 549520699 ticks.
The test code:
long timeIn = 0;<br />
long timeOut = 0;<br />
<br />
long l = System.DateTime.Now.Ticks;<br />
for (long x = 0; x < 10000000000; x++)<br />
{<br />
int i = 1;<br />
i++;<br />
}<br />
timeIn = System.DateTime.Now.Ticks - l;<br />
<br />
l = System.DateTime.Now.Ticks;<br />
int i2;<br />
for (long x = 0; x < 10000000000; x++)<br />
{<br />
i2 = 1;<br />
i2++;<br />
}<br />
timeOut = System.DateTime.Now.Ticks - l;<br />
<br />
MessageBox.Show("Time In: " + timeIn.ToString() + Environment.NewLine + "Time Out: " + timeOut.ToString());<br />
Hogan
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Indeed, I found the same thing last week.
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So the measured difference is less than 1% which is I guess well below
your measurement accuracy: you are measuring elapsed time (good) over
a long period (50 sec, good), but circumstances vary: there are hundreds
of threads in an idle system, watching each and every part of your machine,
there are disk transfers with DMA, there is a varying amount of Ethernet
traffic including broadcast messages you are not interested in, etc etc.
So my first impression is the execution times are the same.
What you could do is reduce the loop count by a factor of 100, run it
100 times, and observe the distribution of the 100 timing results.
The disappointment is neither the C# compiler nor the JIT compiler was
smart enough to recognize the entire loop body could and should be moved
outside, and then the loop is without subject; so it should have been
hundred ticks at most !
On a non-CLR language (such as good old C) it takes quite some tricks
to prevent the compiler from throwing it all out, and still get an
accurate measurement !
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Hi,
This is related to the formatting, not the topic, of your message.
I am preparing an article on copying code snippets from a CodeProject message board to
Visual Studio; seems there are no problems when the browser used is FireFox, Safari, ...
but often problems arise when using Internet Explorer.
One of the factors is the tags that are present inside the < PRE> </PRE> block.
In your message the lines are separated by <br> tags; most other messages have
just regular newlines.
Could you please tell me how you get that, i.e. what tools you use, and how you go
about it. Thanks in advance.
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I'm not really sure if I understood what you mean, hence I don't know if this is the answer your after...
I use Maxthon browser, and when inserting code snippets to my posts I wrap the <code></code> tags inside of the <pre></pre> tags, and not the other way around.
If you could explain again, maybe I would be able to give you a better answer.
Regards,
Shy.
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Thanks, that is exactly what I wanted to know.
I am not familiar with Maxthon browser, I never heard of it.
The background is: if I select (part of) your code snippet using Internet Explorer,
then copy it in Visual Studio, all formatting is lost, there are no line breaks
any more.
I created a utility that improves the situation in most cases; with it I
manage to get newlines, and most of the time the indentation remains intact too;
on your code snippet, with the tool, I do get newlines (so that is an
improvement) but now I loose indentation.
My article will suggest people use the PRE tags without adding CODE tags to it;
could you please give that a try, so just reply to this message, and insert
a code snippet as you usually do (that is using PRE tags) but this time
without using CODE tags.
Thanks in advance.
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Hi All,
I have 2 project in my workspace - first one is some old project that was written in visual C++ and the second one is some project that i writing now in visual C# ( using visual studio 2005 ).
I need to call some method (static method ) and using some enum and even create some object that i have in the C++ project.
My question is how i create the connection between them ?
How can i "include" the classes from C++ in my C# project ?
Thanks for any help.
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Compile your C++ project with the /clr compiler switch. Make your C++ classes be ref classes. Then you can talk to them and instantiate them just fine from any .NET language, including C#.
For more information, see this article on C++/CLI[^].
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Can i do it without compile my C++ project with clr on ?
I don't want to change anything in the C++ project - This project was develop with visual studio 6 and i cant touch the source code.
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There are really 3 ways of dealing with native code in C#:
- P/Invoke[^]: allows you to call exported C functions (not C++ class member functions).
- C++/CLI like I just mentioned
- COM interop: if the C++ dll compiles into a COM object, you can use it easily from C# by simply adding a reference to the COM object like you would a normal .NET control.
If you can't touch the C++ code, could you instead build a new C++/CLI dll that uses the native C++ class under the hood? That way, your C# could talk to the C++/CLI just fine, and under the hood your C++/CLI calls would just go to the native C++ classes.
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Hello all, I am working on debugging a web application. I need to make a boolean value equal to true, false or null. Is it possible to make it null?
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I don't believe you can set a boolean to null. Why do you need to set it to null, why will false not suffice?
I get all the news I need from the weather report - Paul Simon (from "The Only Living Boy in New York")
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Justin Perez wrote: Why do you need to set it to null, why will false not suffice?
I would imaging that something can be true, something can be false and something can be unknown (hence null). There is a distict semantic difference between false and unknown.
I used a language, many years ago, that had the key words true, false and maybe which was used by functions like PointInPolygon(somePoint, somePolygon) the result was true if the point was inside the polygon, false if outside the polygon and maybe if it was on the line.
Upcoming events:
* Glasgow: Mock Objects, SQL Server CLR Integration, Reporting Services, db4o, Dependency Injection with Spring ...
"I wouldn't say boo to a goose. I'm not a coward, I just realise that it would be largely pointless."
My website
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Duh, same as setting an int to null 
I get all the news I need from the weather report - Paul Simon (from "The Only Living Boy in New York")
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You should set set it to false. Boolean is supposed to hold either true or false.
"Real programmers just throw a bunch of 1s and 0s at the computer to see what sticks" - Pete O'Hanlon
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If he's going to be grabbing the value from a database, null could be a "valid" entry.
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