I have a QHash<QString,QString>.
I use the following expression to check whether a value is there in the QHash::keys() or not.
//programme
QHash<QString,QString> samplehash;
QString value = "somevalue";
if(samplehash.contains(value)) // Condition - 1
{
//some code
}
Sometimes the above conditions matches, sometimes not for the same letters of different case. Is the QHash::contains method case-sensitive?
QHash.contains() is case sensitive as John T mentioned. Without the code there is not much to figure out. You can imagine it doing a == between the keys.
Please do not forget that accessing a non existent element via [] will create an empty entry in the hash, this might be what causes your bug. contains does not insert an entry into the hash, neither does value
It is case sensitive. The common practice for handling data from multiple sources and comparing it is to convert it all to the same format first, which usually involves making everything lowercase prior to comparison.
This is a common practice, especially on websites for handling logins, or user input in applications to avoid the old 'PEBKAC' situations and make it easier for users.
One solution could be to subclass QString and override the operator== to do the comparison with case-insensitive mode, using QString::compare.
But the solution of John T is definitely better if it fits your constraints.
Related
As the documentation said
Do not store Contexts inside a struct type; instead, pass a Context explicitly to each function that needs it. The Context should be the first parameter, typically named ctx
but I found, in the typical http request handle function, a http.Request object has .Context() method can retrieve the context which http request associate with.
So why recommend to use context as the first parameter in these functions? Is that reasonable in this situation?
I know that is not an absolute rule. But I want to know why the HandlerFunc is func(ResponseWriter, *Request) instead of func(context.Context, ResponseWriter, *Request).
Apparently HandlerFunc breaks this recommendation.
As described in the documentation you quoted above, ctx should be a (very) common argument for many functions. This is similar to the way many functions return an error. The best place for a common argument/return value is either as the first, or last in a list. (Arguably, Go could have chosen to make error always be the first return value--I won't discuss that here).
Since variadic variables may only be the last in the list of function arguments, this leaves the only option for a common argument to be the first one.
I expect this is why ctx is always first.
This pattern is often seen with other variables in Go (and other languages) as well. Any time a common variable is used by a set of related functions, that common variable often comes first in the argument list (or possibly second, after ctx).
Contrary to the advice you quoted, there are libraries that store ctx in a struct, rather than passing it around as the first argument. These are usually (always?) libraries which had to be retro-fitted to use ctx, long after the library contract was set in stone (by the Go 1.x compatibility guarantee).
Generally, you should follow the advice to pass ctx as the first argument, for any new work.
I'm implementing drag/drop behavior in my model, which is derived from QAbstractItemModel. My code (C++) for the drop event looks something like this:
beginInsertRows(destination_index, row, row);
destination->AcquireDroppedComponent(component);
endInsertRows();
The call to AcquireDroppedComponent can fail for a number of reasons and reject the drop, in which case no new rows will be inserted in the index stored in destination_index. My question is will calling begin/endInsertRows cause problems if this happens? My limited testing on Windows 7 so far shows no undesirable behavior, but I want to be thorough and not rely on the specific behavior of one platform. I can check beforehand if the drop will succeed or not, but I'd like to avoid the extra code if I can. My question also applies for the other begin/end functions like beginRemoveRows, beginInsertColumns, etc.
Calling these methods without doing the actions you indicate breaks their contract. How the clients of your model will cope with that is essentially undefined.
I can check beforehand if the drop will succeed or not, but I'd like to avoid the extra code if I can.
That "extra" code is absolutely necessary.
I'd refactor your code to perform acquisition and model change separately:
if (destination->acquireDroppedComponent(component)) {
beginInsertRows(destination_index, row, row);
destination->insertDroppedComponent(component);
endInsertRows();
}
The acquireDroppedComponent would store the data of the dropped object without modifying the model, and return true if it was successful and the data is usable. You then would call insertDroppedComponent to perform the model change.
How can I tell the Closure Compiler not to rename an inner function? E.g., given this code:
function aMeaninglessName() {
function someMeaningfulName() {
}
return someMeaningfulName;
}
...I'm fine with Closure renaming the outer function (I actively want it to, to save space), but I want the function name someMeaningfulName left alone (so that the name shown in call stacks for it is "someMeaningfulName", not "a" or whatever). This despite the fact that the code calling it will be doing so via the reference returned by the factory function, not by the name in the code. E.g., this is purely for debugging support.
Note that I want the function to have that actual name, not be anonymous and assigned to some property using that name, so for instance this is not a duplicate of this other question.
This somewhat obscure use case doesn't seem to be covered by either the externs or exports functionality. (I was kind of hoping there'd be some annotation I could throw at it.) But I'm no Closure Compiler guru, I'm hoping some of you are. Naturally, if there's just no way to do that, that's an acceptable answer.
(The use case is a library that creates functions in response to calls into it. I want to provide a version of the library that's been pre-compressed by Closure with SIMPLE_OPTIMIZATIONS, but if someone is using that copy of the library with their own uncompressed code and single-stepping into the function in a debugger [or other similar operations], I want them to see the meaningful name. I could get around it with eval, or manually edit the compressed result [in fact, the context is sufficiently unique I could throw a sed script at it], but that's awkward and frankly takes us into "not worth bothering" territory, hence looking for a simple, low-maintenance way.)
There is no simple way to do this. You would have to create a custom subclass of the CodingConvention class to indicate that your methods are "local" externs (support for this was added to handle the Prototype library). It is possible that InlineVariables, InlineFunctions, or RemoveUsedVariables will still try to remove the name and would also need to be fixed up.
Another approach is to use the source maps to remap the stack traces to the original source.
read the following section
https://developers.google.com/closure/compiler/docs/api-tutorial3#export
Two options basically, use object['functionName'] = obj.functionName or the better way
use exportSymbol and exportProperty both on the goog object, here is the docs link for that
http://closure-library.googlecode.com/svn/docs/closure_goog_base.js.html
-- edit
ah, i see now, my first answer is not so great for you. The compiler has some interesting flags, the one which might interest you is DEBUG, which you can pass variables into the compiler which will allow you to drop some debugging annotations in via logging or just a string which does nothing since you are using simple mode.
so if you are using closure you can debug against a development version which is just a page built with dependiencies resolved. we also the drop the following in our code
if(DEBUG){
logger.info('pack.age.info.prototype.func');
}
I came across this interesting function in a piece of ASP Classic that I maintain. At first I laughed, shook my head, then cried (only a little). But then I started to wonder if there is any legitimate reason why 999999999999999 would apparently be considered NULL since VBScript has its quirks. As mentioned in comments, the values passed to this function are returned from the COM dll.
Can anyone confirm if there is some legitimate reason for this or is it ripe for submission to TheDailyWTF.
function NullNumberCheck(Value)
if IsNumeric(Value) then
if Value = 999999999999999 then
Value = ""
end if
end if
NullNumberCheck = Value
end function
That looks like a case of "magic null" in the source of the data - is there a column in the database that backs the values being passed to this function which is not nullable?
Why are people using magic values instead of null in their code?
The author is using this as a method of clearing or unsetting the variable. By setting the value of Value to an empty string, it clears any previous value. The author could have just as easily set it equal to 0, vbNull, or vbEmpty. It really depends on what you are doing with the value later in your script. If you go on to perform further checks on the variable, setting it to vbNull may not be advisable and setting it equal to vbEmpty may crash your script if you are using Option Explicit.
So to answer your question, no this is not a valid way to check for a "null" value, because it's not a comparison operation at all, it's performing a variable assignment.
To check for a null value you can use the IsNull function built into VBscript
http://www.w3schools.com/vbscript/func_isnull.asp
VBScript on ASP Classic contains an "int" function. (It rounds numbers towards -∞.) Suppose that some excessively "clever" coder has created a global variable named "int". Is there any way to get at the original function? I've tried all manner of workarounds with scoping and dodgy execs, but no dice. I suspect that it is impossible, but I'm hoping that someone will know more about it than I do.
EDIT: Thanks for the responses. Since y'all asked, the global variable, called "Int" (though unfortunately, vbscript is not case-sensitive), is a factory for a class similar to Java's Integer. The default property is essentially a one-arg constructor; i.e. "Int(42)" yields a new IntClass object holding 42. The default property of IntClass in turn simply returns the raw number.
The creator was trying to work around the lack of proper namespaces and static methods, and the solution's actually pretty seamless. Pass in an IntClass where an int is expected and it will automatically trigger the default property. I'm trying to patch the last remaining seam: that external code calling "int" will not round properly (because the constructor uses CLng).
Not that I know of, getref only works on custom functions not on build-ins. I would suggest renaming the custom'int' function and update all references to this custom ones. You can use the search function visual studio (express) or any other tool of your liking for this. Shouldn't be to much work.
I didn't think reserved words would be allowed for function names or variables.
Duncanson's right. Do the pain and rename int. Chances are there are worse things going on than just this.
(why would someone make a global variable named int... that's going to take some thinking)
Or you can use CInt instead on Int
response.write trim(cint(3.14)) + "<br>"
Wrong!!
See NobodyMan comments