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Hi all,
I was learning yield operator. And made a function like this.
public IEnumerable<Guid> GetIds(int count, DateTime time)
{
Console.WriteLine("Start");
{
if (DateTime.Now > time)
yield break;
else
yield return Guid.NewGuid();
}
Console.WriteLine("End");
}
But End never get printed.Can anyone tell why? Because after break statement it should get out of the loop and print it.
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(what loop?)
yield break does not break out of a loop, it "signals the end of the iterator", or as msdn also says:
"In a yield break statement, control is unconditionally returned to the caller of the iterator"
Source: http://msdn.microsoft.com/en-us/library/9k7k7cf0.aspx[^]
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From the relevant MSDN page for break:
The break statement terminates the closest enclosing loop or switch statement in which it appears. Control is passed to the statement that follows the terminated statement, if any.
So break breaks out of loops and switch statements. I am guessing that in this case it breaks out of your method.
Same for yield:
Used in an iterator block to provide a value to the enumerator object or to signal the end of iteration.
Once again yield is meant to be used in an iteration. if is not strictly speaking an iteration, although I suspect that your else block would run.
The pages I looked at did not say what these statements do when not used in iterations.
Henry Minute
Do not read medical books! You could die of a misprint. - Mark Twain
Girl: (staring) "Why do you need an icy cucumber?"
“I want to report a fraud. The government is lying to us all.”
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Because you terminate the method before you get there.
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Thanks to all for answers.
I got the point. Whenever we write yield it returns IEnumerable to the caller.And once yield statement get executed, no statements get executed.
Thanks again..
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One thing - when you built the code, did it not warn you that an unreachable condition had been detected? It's important to pay attention to warnings as well.
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Pete O'Hanlon wrote: did it not warn you that an unreachable condition had been detected?
I am using VS2008 and there was no warning.
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I find that surprising. Certainly, in VS2010 there is a warning - check to make sure that you haven't deselected the warnings checkbox.
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Pete O'Hanlon wrote: Certainly, in VS2010 there is a warning
If I had had VS2010, I would've checked in VS2010. But in VS 2008, there is no warning for this.I got warning for something else(just to check, whether it is showing warning or not)
And if it is showing warning in VS2010, then might be a Bug in VS2008 
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No warning in VS2008 Express Edition (warning level = 4).
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It seems to be a problem with it being in the if block - put it outside and it warns, inside and it doesn't - but it should.
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I agree, however I'm not surprised they did get it wrong at first: yield return statements are not really breaking program flow like regular returns would (they somewhat resemble a UNIX fork), however yield break does break the flow.
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Indeed, which is why I'd have expected yield break to throw a warning.
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Hello everyone,
Currently I am building in my company system that includes all the scripts that coordinate them.
all so you can run scripts only from people Aspcfeim will only permissions.
Anyone ever built something like this? Does anyone have suggestions?
This course will build on WPF C #.
Thanks,
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I have a DataGridView and I have a column where the user usually only enters in 6 set things, however sometimes they need to input something different. The default ComboBox column offered for DataGridView objects does not allow typing items. How can I add a column where I can use a combo box to do a lookup if I want.
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#region Enable Typing in DataGridViewComboBoxColumn
private void dgvPhone_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
try
{
if (this.dgvPhone.CurrentCellAddress.X == 2)
{
ComboBox cb = e.Control as ComboBox;
if (cb != null)
{
cb.DropDownStyle = ComboBoxStyle.DropDown;
cb.AutoCompleteMode = AutoCompleteMode.SuggestAppend;
}
}
}
catch (Exception ex)
{
clsErrorHandle.GetError(ex);
}
}
#region Enable Add new items Dynamically to DataGridViewComboBoxColumn
private void dgvPhone_CellValidating(object sender, DataGridViewCellValidatingEventArgs e)
{
try
{
if (this.dgvPhone.CurrentCellAddress.X == 2)
{
if (!ColPhoneType.Items.Contains(e.FormattedValue) && !clsMain.IsObjectNullorEmpty(e.FormattedValue))
{
ColPhoneType.Items.Add(e.FormattedValue);
DataRow drPhone = dtPhoneType.NewRow();
drPhone["PhoneType"] = e.FormattedValue;
dtPhoneType.Rows.Add(drPhone);
}
dgvPhone.Rows[e.RowIndex].Cells[e.ColumnIndex].Value = e.FormattedValue;
}
}
catch (Exception ex)
{
clsErrorHandle.GetError(ex);
}
}
#endregion
#endregion
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See if this[^] thread helps
The funniest thing about this particular signature is that by the time you realise it doesn't say anything it's too late to stop reading it.
My latest tip/trick
Visit the Hindi forum here.
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Very good!
For your next trick: Tying your own shoelaces!
Idiot.
Real men don't use instructions. They are only the manufacturers opinion on how to put the thing together.
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There is a rule not to belittle posters in the programming forums. It is a good rule I always follow.
But for you Sajid, I'll make an exception.
Go, go a long way away and don't come back. Ever.
Panic, Chaos, Destruction.
My work here is done.
or "Drink. Get drunk. Fall over." - P O'H
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If you drop your car keys into a pool of molten lava, let them go, because man, they're gone.
.45 ACP - because shooting twice is just silly
-----
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
-----
"The staggering layers of obscenity in your statement make it a work of art on so many levels." - J. Jystad, 2001
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I've spent the last two evenings writing a routine to import .csv files to a SQL Server database - not that I'm anywhere near to done yet... So far I've got a parser that can read multiple files selected from an OpenFileDialog, and strip most of the crap out of them, then appending the records to a file that will be used for later import into a dataset and INSERTed to a SQL Server DB. But there's a sticky bit I'd like some advice about...
Every day I receive power meter readings from our supplier, the Western Area Power Administration (WAPA), that give me the power received from them through several meters, broken down by hourly brackets. Each transmission (via email) includes header lines that can contain anything at all, but thankfully cannot be parsed by the Split() method. My program, so far, strips all of them out. There's also a final line that tells me how many records are included, which I also ignore. But there's also a record that yields the total from all meters which I don't want to include. The mystery here is that, when I use the Split() method on a line I've read from the file, the array returned seems to be 1-based, not 0-based. I can clearly see in Notepad that the first field returned is a date value, but accessing that date requires using Split[1]. I can tell, for instance, that the beginning of real data has been reached by testing Split[1] for a valid date. I ignore everything before that discovery. The totals line that I want to ignore also contains a valid date in the Split[1] field, followed by a blank space in the next field. I tried skipping lines that have a blank space in the second field, Split[2], but that didn't work.
What I'm thinking is that, since I do have all the relevant data sent to a file with proper delimiters, maybe it would be better to just import what I have to SQL Server and let a query sort out the rows with missing fields. Whatcha think?
Will Rogers never met me.
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If you read the CSV through OleDb connection, you can get the data in a table. That way I suppose it will be easy to get and save the relevant data.
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Hi Roger,
Roger Wright wrote: maybe it would be better to just import what I have to SQL Server and let a query sort out the rows with missing fields
I don't think so. Partly because my knowledge of SQL is limited, mainly because I don't want to feed data I don't understand well to another big system. Separation of concerns: first clean up the data, then process it.
Some comments:
1.
a small data sample could have been helpful.
2.
How big is a typical file? Maybe header and tail removal could be handled best by Regex.
3.
I would be worried if relevant data ends up in array element 1 when you expect it in element 0. No, Split is not 1-based at all. You probably have an unexpected character somewhere (maybe your line separators are CR+LF, and one of them becomes the first char of your line?); I would analyze this and deal with it properly. Don't rely on code that seems to fix something you don't understand.
4.
I guess you want reliability and flexibility; i.e. the data format might slightly change over time (or vary from file to file), and you probably want that to get handled correctly, and when a problem occurs to get noticed right away. It would suck if there wasn't some kind of checksum. You did mention a total you want to skip; I would not skip it, I would try and recognize it (the last useful data line of the file?), compare it to the sum of all the previous data I recognized, and when equal, just skip it; when unequal, raise an alarm.
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Good points, all of them. As for a sample:
Date Range = Yesterday (09/01/2010)
Time Zone = MST
Sign Convention = GEN + LOAD + OTHER +
Include Zero = Yes
Execution Time: 09/02/2010 07:00 CST
"Zone = RMS / AMPS"
"Date","Meter","HE1","HE2","HE3","HE4",...,"HE24","On Peak","Off Peak","Total"
"09/01/2010","BCI891 ","0.000","0.000","0.000","0.000",...,"0.000","45.000","0.000","45.000"
"","DAD348 Out","0.000","0.000","0.000","0.000",...,"4.634","4.382","75.264","9.016","84.280"
"","NON921A Out","-6.200","-5.800","-5.600","-5.300",...,"-7.300","-150.700","-49.200","-199.900"
"","TOP928 In","0.000","0.000","0.000","0.000",...,"0.000","0.000","0.000","0.000"
"","TOP928 Out","7.490","6.940","6.740","6.440",...,"8.750","179.920","58.980","238.900"
"09/01/2010","","1.290","1.140","1.140","1.140",...,"5.832","149.484","18.796","168.280"
Total: 5 records
The above is typical, exported from Excel as a .csv file and emailed to me by an automated system. The headings HEx mean "Hour Ending", so I edited out most of them, as they aren't relevant to seeing the pattern. I've taken your suggestion and read up on Regex - what a pain! I don't know when it changed, but it's no longer possible to print "this topic and all sub-topics" from the VS2008 Help system.
In looking at it tonight, I think I see an approach that is fairly simple. As I read each line, I can look at the first 4 or 5 characters and tell what kind of line it is, dumping any that aren't data lines. The String.Length() function will make it easy to drop blank lines, too. A line that begins with a date is then either the beginning of data, or the summary line with column totals, and a little string footwork can patch the date into the lines that are missing that item so that they all have the same format. A Regex will be handy to extract the number of lines from the last line, just to make sure I've got all of it in my result set.
I'm not sure what to do with all the data values that should be numerics - I'd like to strip all the quotes out before importing to a dataset, excepting the text containing the meter name, to save having to do conversions from string to float after I import them, but that seems like more than it's worth. I hate to hardcode formats into the program, just in case the format changes one day, but I don't see any way around it.
Thanks for the suggestions! 
Will Rogers never met me.
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