Strange Behavior

[Jon Vaughan]

I have a static struct :

public static LocationPaging stLocationPaging = new LocationPaging();

Which is made up from :

public struct LocationPaging

{

public int Page;

public int MaxPage;

}

Which is used to control the paging of some records. BUT , when I call :

Scanning.stLocationPaging.Page = Scanning.stLocationPaging.Page + 1;

The increment doesn't occur, im quite new to C# , but im sure I have done
this in VB.Net with no issues. What am I over looking ?

[Jon Vaughan]

Ignore the above , I was resetting it back to 1 in my code :(
How embarassing !

"Jon Vaughan" <jo**********@hotmail.comwrote in message
news:1S*********************@fe12.news.easynews.co m...

>I have a static struct :

public static LocationPaging stLocationPaging = new LocationPaging();

Which is made up from :

public struct LocationPaging

{

public int Page;

public int MaxPage;

}

Which is used to control the paging of some records. BUT , when I call :

Scanning.stLocationPaging.Page = Scanning.stLocationPaging.Page + 1;

The increment doesn't occur, im quite new to C# , but im sure I have done
this in VB.Net with no issues. What am I over looking ?

[Jon Skeet [C# MVP]]

Jon Vaughan wrote:

I have a static struct :

public static LocationPaging stLocationPaging = new LocationPaging();

Which is made up from :

public struct LocationPaging
{
public int Page;
public int MaxPage;
}
Which is used to control the paging of some records. BUT , when I call :

Scanning.stLocationPaging.Page = Scanning.stLocationPaging.Page + 1;
The increment doesn't occur, im quite new to C# , but im sure I have done
this in VB.Net with no issues. What am I over looking ?

Could you post a short but complete example which demonstrates the
problem? Here's a short but complete example which shows it working:

using System;

public struct LocationPaging
{
public int Page;
public int MaxPage;
}

class Test
{
static LocationPaging Foo;

static void Main()
{
Test.Foo.Page = Test.Foo.Page+1;
Console.WriteLine (Test.Foo.Page);
Test.Foo.Page = Test.Foo.Page+1;
Console.WriteLine (Test.Foo.Page);
}
}

Jon

[Marc Gravell]

Well, as presented it seems to just about work for me - i.e. the value
increments, but I suspect you are hitting one of the following:

1: value-type handling: if the struct is accessed e.g. through a
property, then the value will be cloned, with you updating the separate
copy
2: volatility: another thread looking at this field directly in a tight
look may not notice the change i.e. the value might be in a register

My first question would be: why is this a struct? It feels like it
should be a class, since you seem to want to share it between callers
(which structs are not geared up to do).

Also - (advisory only) - a: accessing fields directly (rather than
through properties) isn't all that recommended; b: since it is static
you may need to make this thread safe (synchronised access) if you are
ever going to do anything complex with threading, otherwise various
gotchas apply. Sounds like this may not be an issue.

But try making it a class; I suspect this will fix everything.

Marc