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What is the “volatile” keyword used for?
...ptimization and caching, and thus is useful when a variable can be changed by another thread.
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Finding ALL duplicate rows, including “elements with smaller subscripts”
...ovide a reproducible example, so here's an illustration kindly contributed by @jbaums
vec <- c("a", "b", "c","c","c")
vec[duplicated(vec) | duplicated(vec, fromLast=TRUE)]
## [1] "c" "c" "c"
Edit: And an example for the case of a data frame:
df <- data.frame(rbind(c("a","a"),c("b","b"),...
SQL Server reports 'Invalid column name', but the column is present and the query works through mana
I've hit a bit of an impasse. I have a query that is generated by some C# code. The query works fine in Microsoft SQL Server Management Studio when run against the same database.
...
Android destroying activities, killing processes
...he next activity will not be resumed until this method
returns. Followed by either onResume() if the activity returns back to
the front, or onStop() if it becomes invisible to the user.
onStop() Called when the activity is no longer visible to the user, because another activity has been res...
Purpose of Unions in C and C++
...son people miss it quite often.
The purpose of union is to save memory by using the same memory region for storing different objects at different times. That's it.
It is like a room in a hotel. Different people live in it for non-overlapping periods of time. These people never meet, and general...
Why does sudo change the PATH?
...
it's annoying. period. if it could 'get you trojaned' by sudo it could get you trojaned the same without it. granted, harder, but if you are running code from the wrong place even with your regular user, then things are already bad enough.
– gcb
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Is the != check thread safe?
...blic boolean test() {
return a != a;
}
may produce true. This is the bytecode for test()
ALOAD 0
GETFIELD test/Test1.a : Ljava/lang/Object;
ALOAD 0
GETFIELD test/Test1.a : Ljava/lang/Object;
IF_ACMPEQ L1
...
as we can see it loads field a to local vars twice, it's a non...
What is the difference between a port and a socket?
This was a question raised by one of the software engineers in my organisation. I'm interested in the broadest definition.
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Selenium wait until document is ready
...ed solution only waits for DOM readyState to signal complete. But Selenium by default tries to wait for those (and a little bit more) on page loads via the driver.get() and element.click() methods. They are already blocking, they wait for the page to fully load and those should be working ok.
Probl...
For i = 0, why is (i += i++) equal to 0?
...is invoked with the saved value of x as its argument.
The value returned by the operator is stored in the location given by the evaluation of x.
The saved value of x becomes the result of the operation.
Note that due to order of precedence, the postfix ++ occurs before +=, but the result...