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Pointer to an element in QList
Qt: Storing a custom object in a collection by valueSplitting QList into chunks, pointers or references?Can two threads read from the same QList at the same time?How to make QList<Type*> work with indexOf() and custom operator==()?QVariant to QList with unkown list template parameterC++ - pointers in a QListNested QHash Not SavingQtConcurrent::map and list of pointersHow would a QList containing pointers behave when passed by valueQHash removal of specified position till the end of QHash and update the QList accordingly
I have a list of lists container with this type:
QList< QList<UAVObject *> > objects;
For some reason I would like to access one of the internal lists quickly. Can I store a pointer to an internal list? For example:
QList<UAVObject *>& ref = objects[0];
QList<UAVObject *>* pt = &ref;
Will the value of pt still be valid across different function calls and original objects manipulations? Let's assume that the objects list will only be added to and never removed from.
qt qt5
asked Mar 8 at 22:38
ilya1725ilya1725
1,85432441
add a comment |
I have a list of lists container with this type:
QList< QList<UAVObject *> > objects;
For some reason I would like to access one of the internal lists quickly. Can I store a pointer to an internal list? For example:
QList<UAVObject *>& ref = objects[0];
QList<UAVObject *>* pt = &ref;
Will the value of pt still be valid across different function calls and original objects manipulations? Let's assume that the objects list will only be added to and never removed from.
qt qt5
asked Mar 8 at 22:38
ilya1725ilya1725
1,85432441
add a comment |
I have a list of lists container with this type:
QList< QList<UAVObject *> > objects;
For some reason I would like to access one of the internal lists quickly. Can I store a pointer to an internal list? For example:
QList<UAVObject *>& ref = objects[0];
QList<UAVObject *>* pt = &ref;
Will the value of pt still be valid across different function calls and original objects manipulations? Let's assume that the objects list will only be added to and never removed from.
qt qt5
asked Mar 8 at 22:38
ilya1725ilya1725
1,85432441
I have a list of lists container with this type:
QList< QList<UAVObject *> > objects;
For some reason I would like to access one of the internal lists quickly. Can I store a pointer to an internal list? For example:
QList<UAVObject *>& ref = objects[0];
QList<UAVObject *>* pt = &ref;
Will the value of pt still be valid across different function calls and original objects manipulations? Let's assume that the objects list will only be added to and never removed from.
qt qt5
qt qt5
asked Mar 8 at 22:38
ilya1725ilya1725
1,85432441
asked Mar 8 at 22:38
ilya1725ilya1725
1,85432441
asked Mar 8 at 22:38
ilya1725ilya1725
1,85432441
asked Mar 8 at 22:38
ilya1725ilya1725
1,85432441
asked Mar 8 at 22:38
ilya1725ilya1725
1,85432441
1,85432441
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
QList is not based on a STL container and has nothing to do with std::list.
The invalidation rules specified for the STL containers are not applicable.
According to the Qt documentation (and my understanding), it uses an array of pointers to the items, unless the item is not larger than a void* and declared as movable (with Q_MOVABLE_TYPE).
In that case, the item is directly stored in the array and the reference will become invalid when your list will grow (the array of pointers will be reallocated).
answered Mar 8 at 23:57
Romha KorevRomha Korev
2,2671423
Ah, that's why they can implement[]access in O(1).
– ilya1725
Mar 9 at 1:31
@ilya1725, compared to stl containers, QList is more of a std::deque, that's why there also exists QLinkedList, which is more of a list
– MasterAler
Mar 9 at 18:23
@MasterAler, I did not know that, thank you. Why not call the containers the way they are, i.e. dequeue and list?
– ilya1725
Mar 11 at 15:11
@ilya1725, well, I just guess that this naming desicion comes from some average practice of Qt container's usage -- it's not an often situation when someone really needs a simple linked list, more likely that someone doesn't want/need QVector, complex server backends is not usually written in Qt, after all =). Thus, QList is multipurpose and efficient for average cases, all classes in designed to be used quickly and easily (like QTcpSocket is not as customizable as real socket, but is very straightforward when used). That's my assumption))
– MasterAler
Mar 13 at 11:09
add a comment |
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1 Answer
1
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oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
QList is not based on a STL container and has nothing to do with std::list.
The invalidation rules specified for the STL containers are not applicable.
According to the Qt documentation (and my understanding), it uses an array of pointers to the items, unless the item is not larger than a void* and declared as movable (with Q_MOVABLE_TYPE).
In that case, the item is directly stored in the array and the reference will become invalid when your list will grow (the array of pointers will be reallocated).
answered Mar 8 at 23:57
Romha KorevRomha Korev
2,2671423
Ah, that's why they can implement[]access in O(1).
– ilya1725
Mar 9 at 1:31
@ilya1725, compared to stl containers, QList is more of a std::deque, that's why there also exists QLinkedList, which is more of a list
– MasterAler
Mar 9 at 18:23
@MasterAler, I did not know that, thank you. Why not call the containers the way they are, i.e. dequeue and list?
– ilya1725
Mar 11 at 15:11
@ilya1725, well, I just guess that this naming desicion comes from some average practice of Qt container's usage -- it's not an often situation when someone really needs a simple linked list, more likely that someone doesn't want/need QVector, complex server backends is not usually written in Qt, after all =). Thus, QList is multipurpose and efficient for average cases, all classes in designed to be used quickly and easily (like QTcpSocket is not as customizable as real socket, but is very straightforward when used). That's my assumption))
– MasterAler
Mar 13 at 11:09
add a comment |
QList is not based on a STL container and has nothing to do with std::list.
The invalidation rules specified for the STL containers are not applicable.
According to the Qt documentation (and my understanding), it uses an array of pointers to the items, unless the item is not larger than a void* and declared as movable (with Q_MOVABLE_TYPE).
In that case, the item is directly stored in the array and the reference will become invalid when your list will grow (the array of pointers will be reallocated).
answered Mar 8 at 23:57
Romha KorevRomha Korev
2,2671423
Ah, that's why they can implement[]access in O(1).
– ilya1725
Mar 9 at 1:31
@ilya1725, compared to stl containers, QList is more of a std::deque, that's why there also exists QLinkedList, which is more of a list
– MasterAler
Mar 9 at 18:23
@MasterAler, I did not know that, thank you. Why not call the containers the way they are, i.e. dequeue and list?
– ilya1725
Mar 11 at 15:11
@ilya1725, well, I just guess that this naming desicion comes from some average practice of Qt container's usage -- it's not an often situation when someone really needs a simple linked list, more likely that someone doesn't want/need QVector, complex server backends is not usually written in Qt, after all =). Thus, QList is multipurpose and efficient for average cases, all classes in designed to be used quickly and easily (like QTcpSocket is not as customizable as real socket, but is very straightforward when used). That's my assumption))
– MasterAler
Mar 13 at 11:09
add a comment |
QList is not based on a STL container and has nothing to do with std::list.
The invalidation rules specified for the STL containers are not applicable.
According to the Qt documentation (and my understanding), it uses an array of pointers to the items, unless the item is not larger than a void* and declared as movable (with Q_MOVABLE_TYPE).
In that case, the item is directly stored in the array and the reference will become invalid when your list will grow (the array of pointers will be reallocated).
answered Mar 8 at 23:57
Romha KorevRomha Korev
2,2671423
QList is not based on a STL container and has nothing to do with std::list.
The invalidation rules specified for the STL containers are not applicable.
According to the Qt documentation (and my understanding), it uses an array of pointers to the items, unless the item is not larger than a void* and declared as movable (with Q_MOVABLE_TYPE).
In that case, the item is directly stored in the array and the reference will become invalid when your list will grow (the array of pointers will be reallocated).
answered Mar 8 at 23:57
Romha KorevRomha Korev
2,2671423
answered Mar 8 at 23:57
Romha KorevRomha Korev
2,2671423
answered Mar 8 at 23:57
Romha KorevRomha Korev
2,2671423
answered Mar 8 at 23:57
Romha KorevRomha Korev
2,2671423
2,2671423
Ah, that's why they can implement[]access in O(1).
– ilya1725
Mar 9 at 1:31
@ilya1725, compared to stl containers, QList is more of a std::deque, that's why there also exists QLinkedList, which is more of a list
– MasterAler
Mar 9 at 18:23
@MasterAler, I did not know that, thank you. Why not call the containers the way they are, i.e. dequeue and list?
– ilya1725
Mar 11 at 15:11
@ilya1725, well, I just guess that this naming desicion comes from some average practice of Qt container's usage -- it's not an often situation when someone really needs a simple linked list, more likely that someone doesn't want/need QVector, complex server backends is not usually written in Qt, after all =). Thus, QList is multipurpose and efficient for average cases, all classes in designed to be used quickly and easily (like QTcpSocket is not as customizable as real socket, but is very straightforward when used). That's my assumption))
– MasterAler
Mar 13 at 11:09
add a comment |
Ah, that's why they can implement[]access in O(1).
– ilya1725
Mar 9 at 1:31
@ilya1725, compared to stl containers, QList is more of a std::deque, that's why there also exists QLinkedList, which is more of a list
– MasterAler
Mar 9 at 18:23
@MasterAler, I did not know that, thank you. Why not call the containers the way they are, i.e. dequeue and list?
– ilya1725
Mar 11 at 15:11
@ilya1725, well, I just guess that this naming desicion comes from some average practice of Qt container's usage -- it's not an often situation when someone really needs a simple linked list, more likely that someone doesn't want/need QVector, complex server backends is not usually written in Qt, after all =). Thus, QList is multipurpose and efficient for average cases, all classes in designed to be used quickly and easily (like QTcpSocket is not as customizable as real socket, but is very straightforward when used). That's my assumption))
– MasterAler
Mar 13 at 11:09
Ah, that's why they can implement
[] access in O(1).– ilya1725
Mar 9 at 1:31
Ah, that's why they can implement
[] access in O(1).– ilya1725
Mar 9 at 1:31
@ilya1725, compared to stl containers, QList is more of a std::deque, that's why there also exists QLinkedList, which is more of a list
– MasterAler
Mar 9 at 18:23
@ilya1725, compared to stl containers, QList is more of a std::deque, that's why there also exists QLinkedList, which is more of a list
– MasterAler
Mar 9 at 18:23
@MasterAler, I did not know that, thank you. Why not call the containers the way they are, i.e. dequeue and list?
– ilya1725
Mar 11 at 15:11
@MasterAler, I did not know that, thank you. Why not call the containers the way they are, i.e. dequeue and list?
– ilya1725
Mar 11 at 15:11
@ilya1725, well, I just guess that this naming desicion comes from some average practice of Qt container's usage -- it's not an often situation when someone really needs a simple linked list, more likely that someone doesn't want/need QVector, complex server backends is not usually written in Qt, after all =). Thus, QList is multipurpose and efficient for average cases, all classes in designed to be used quickly and easily (like QTcpSocket is not as customizable as real socket, but is very straightforward when used). That's my assumption))
– MasterAler
Mar 13 at 11:09
@ilya1725, well, I just guess that this naming desicion comes from some average practice of Qt container's usage -- it's not an often situation when someone really needs a simple linked list, more likely that someone doesn't want/need QVector, complex server backends is not usually written in Qt, after all =). Thus, QList is multipurpose and efficient for average cases, all classes in designed to be used quickly and easily (like QTcpSocket is not as customizable as real socket, but is very straightforward when used). That's my assumption))
– MasterAler
Mar 13 at 11:09
add a comment |
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