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You can't: to return a reference the returned object must exist outside the function scope. To "solve" the issue you must either change the signature to
Contact GloballAll::getContactByUID()or to something likebool GloballAll::getContactByUID( ..., Contact& return )This post is deleted! -
@VRonin said in How to return myclass reference?:
Contact* GlobalAll::getContactByUID(const int &UID) {
Actually I don't see why that is any better than returning nothing at all,
void GlobalAll::getContactByUID(const int &UID) { ...@Wieland I think this is a search function so it must return a "reference" to the object with
contact.UID==UIDor null if it can't find the item.P.S.
If you find yourself using this function a lot, consider changingallContactsinto aQHash<int,Contact>and use theUIDas key"La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
~Napoleon BonaparteOn a crusade to banish setIndexWidget() from the holy land of Qt
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@Wieland I think this is a search function so it must return a "reference" to the object with
contact.UID==UIDor null if it can't find the item.P.S.
If you find yourself using this function a lot, consider changingallContactsinto aQHash<int,Contact>and use theUIDas key@VRonin said in How to return myclass reference?:
or null if it can't find the item.
No. Contact will be in my QList.
@VRonin said in How to return myclass reference?:
If you find yourself using this function a lot, consider changing allContacts into a QHash<int,Contact> and use the UID as key
I do not know about QHash <T, T>, It's faster than a binary search?
If my allContacts.size() == 10 000, 15 Checks i need maximum.Do what you want.
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@VRonin said in How to return myclass reference?:
or null if it can't find the item.
No. Contact will be in my QList.
@VRonin said in How to return myclass reference?:
If you find yourself using this function a lot, consider changing allContacts into a QHash<int,Contact> and use the UID as key
I do not know about QHash <T, T>, It's faster than a binary search?
If my allContacts.size() == 10 000, 15 Checks i need maximum. -
@jsulm @VRonin Thank guys.
Also there are good example http://developers-club.com/posts/170017/@VRonin said in How to return myclass reference?:
If you find yourself using this function a lot, consider changing allContacts into a QHash<int,Contact> and use the UID as key
I think you are right. Thank.
how much seconds will be lost if I search an element in QList one milion times(if i use binary search) and how much will be reserved in QHash?Do what you want.
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@jsulm @VRonin Thank guys.
Also there are good example http://developers-club.com/posts/170017/@VRonin said in How to return myclass reference?:
If you find yourself using this function a lot, consider changing allContacts into a QHash<int,Contact> and use the UID as key
I think you are right. Thank.
how much seconds will be lost if I search an element in QList one milion times(if i use binary search) and how much will be reserved in QHash?@Taz742 said in How to return myclass reference?:
how much seconds will be lost if I search an element in QList one milion times and how much will be reserved in QHash?
Searching in a list is O(n). Statistically you will need n/2 comparisons to find what you're looking for. Hash is O(1) - so much faster. For lookup you should use QHash or QMap not QList.
You you want to see the difference then just write a small app and measure the time...
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@jsulm @VRonin Thank guys.
Also there are good example http://developers-club.com/posts/170017/@VRonin said in How to return myclass reference?:
If you find yourself using this function a lot, consider changing allContacts into a QHash<int,Contact> and use the UID as key
I think you are right. Thank.
how much seconds will be lost if I search an element in QList one milion times(if i use binary search) and how much will be reserved in QHash?@Taz742 said in How to return myclass reference?:
how much seconds will be lost if I search an element in QList one milion times(if i use binary search) and how much will be reserved in QHash?
Algorithmic complexity isn't measured in seconds, but with the so called "big O notation" (asymptotic complexity). Provided you can do a binary search, which implies the list is kept at all times ordered, then the complexity of the search is
O(logN). For a hash it'sO(1)with worst-caseO(N). Now, there are nuances, but most of the time a hash would fare better than a red-black tree (QMap), which would be better than keeping an ordered list and doing a binary search on it. Of course the best is to have everything in a vector and just get the elements by index, but that's not always possible. -
- Simple code is better than complex code.
- Only sacrifice simplicity if you have proof that your code is too slow.
- The only way to prove that your code is too slow is by measuring execution time against real world data on the target machine.
- Don't just assume that algorithmic complexity dominates execution time; you have to measure it.
Just my 2 cents.
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- Avoid premature pessimization - by default use data structures and algorithms which are right for the job, without sacrificing simplicity.
Otherwise you may get a death of thousand cuts for performance of your application, when it's not enough to fix a few bottlenecks because all code if uniformly slow.
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- Avoid premature pessimization - by default use data structures and algorithms which are right for the job, without sacrificing simplicity.
Otherwise you may get a death of thousand cuts for performance of your application, when it's not enough to fix a few bottlenecks because all code if uniformly slow.
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