BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Vector of TPanels? Goto page 1, 2  Next          BorlandTalk.com Forum Index -> C++ Builder (Language C++) View previous topic :: View next topic   Author Message Rory Walsh Guest Posted: Sat Mar 26, 2005 5:09 pm    Post subject: Vector of TPanels? I want to create a vector of TPanels that I dynamically create with a press of a button. I then want to dynamically delete them and not leave a whole in the vector list. I have successfully done this with simple integers but I am having problems with TPanels. This is the syntax I used for the integers and it worked: int *tempX = m_PointsX.begin()+5;//delete the fifth element m_PointsY.erase(tempY); My TPanel vector does not have a begin() and end() so I tried it with front() but I get errors when I compile: TPanel* temp = m_Points.front()+5; m_Points.erase(temp); How do I go about erasing the 5th element from this vector? Any ideas? Where have vectors been my whole life, there great! Back to top Alisdair Meredith Guest Posted: Sat Mar 26, 2005 6:02 pm    Post subject: Re: Vector of TPanels? Rory Walsh wrote: Quote: This is the syntax I used for the integers and it worked: int *tempX = m_PointsX.begin()+5;//delete the fifth element m_PointsY.erase(tempY); However, it is not guaranteed to work on all implementations. You have made a (reasonable) assumption that vector iterators will be simple pointers. vector is deliberately designed so this is possible, but it is not required. Many other standard libraries usea specific type for vector::iterator, that can support extra options when debugging. The 'correct' way to write this would be: vector<int>::iterator tempX = m_PointsX.begin()+5; m_PointsY.erase(tempY); If you use vector<int>::iterator a lot, you may want to create a typedef for it! Also note that many standard algorithms are function templates, so they will automatically deduce the correct type for you, simply by passing the arguments. This means that in my code, I rarely see the iterators named: m_PointsY.erase( m_PointsX.begin() + 5 ); Quote: My TPanel vector does not have a begin() and end() so I tried it with front() but I get errors when I compile: Uh oh, this sounds a bit wierd! Could you show me the code you use to fill your vector<TPanel *> with panels? AlisdairM(TeamB) Back to top Rory Walsh Guest Posted: Sat Mar 26, 2005 6:34 pm    Post subject: Re: Vector of TPanels? I basically have a button that does this each time I press it { m_Points[incr] = new TPanel(Image1); m_Points[incr]->Parent = Panel1; incr++; } I have left out the other stuff for clarity, but that basically it? Is this ok? Alisdair Meredith wrote: Quote: Rory Walsh wrote: This is the syntax I used for the integers and it worked: int *tempX = m_PointsX.begin()+5;//delete the fifth element m_PointsY.erase(tempY); However, it is not guaranteed to work on all implementations. You have made a (reasonable) assumption that vector iterators will be simple pointers. vector is deliberately designed so this is possible, but it is not required. Many other standard libraries usea specific type for vector::iterator, that can support extra options when debugging. The 'correct' way to write this would be: vector<int>::iterator tempX = m_PointsX.begin()+5; m_PointsY.erase(tempY); If you use vector<int>::iterator a lot, you may want to create a typedef for it! Also note that many standard algorithms are function templates, so they will automatically deduce the correct type for you, simply by passing the arguments. This means that in my code, I rarely see the iterators named: m_PointsY.erase( m_PointsX.begin() + 5 ); My TPanel vector does not have a begin() and end() so I tried it with front() but I get errors when I compile: Uh oh, this sounds a bit wierd! Could you show me the code you use to fill your vector<TPanel *> with panels? AlisdairM(TeamB) Back to top Alisdair Meredith Guest Posted: Sat Mar 26, 2005 7:10 pm    Post subject: Re: Vector of TPanels? Rory Walsh wrote: Quote: I basically have a button that does this each time I press it { m_Points[incr] = new TPanel(Image1); m_Points[incr]->Parent = Panel1; incr++; } I have left out the other stuff for clarity, but that basically it? Is this ok? It depends on whether or not you have pre-filled your vector with null pointers. I would prefer to do this with m_points.push_back( new TPanel(Image1) ); This expands the vector by 1 element, and puts the panel in it. Likewise, to remove the last element of the vector: m_points.pop_back(); If you have not filled your vector in the constructor, then your calls to m_points[] above would be the same as indexing from an array you have not allocated: int *x; // = new int[5] missing x[3] = 5; // Oops! Note that while you can put pointers in and out of vector quite easily, you still need to manage the memory. Ultimately, everything that is newed should be deleted. In your case you will not leak memory, as the VCL library will guarantee all your panels are deleted when their owner, Image1, is destroyed. However, if Image1 is deleted before your vector, you will have a vector full of invalid pointers! THat is why I use the shared_ptr 'smart pointer' from the Boost library. This class acts just like a pointer, but also wraps that pointer with a reference count. When the last shared_ptr holding onto a pointer dies, it calls delete. Take a look at www.boost.org for details, but beware. The whole library has grown quite big and scary over the years! AlisdairM(TeamB) Back to top Duane Hebert Guest Posted: Sat Mar 26, 2005 7:21 pm    Post subject: Re: Vector of TPanels? "Alisdair Meredith" <alisdair.meredith@no-spam-splease (AT) uk (DOT) renaultf1.com> wrote Quote: Take a look at www.boost.org for details, but beware. The whole library has grown quite big and scary over the years! Quite big, I agree with Alisdair. What's scary are the years that I didn't use it <g> Back to top Rory Walsh Guest Posted: Sat Mar 26, 2005 8:05 pm    Post subject: Re: Vector of TPanels? Thanks for the pointers, pardon the pun! I'll keep grafting away at it. It's making more sense now. I can't believe that I have never used vectors before? Cheers, Rory. Duane Hebert wrote: Quote: "Alisdair Meredith" <alisdair.meredith@no-spam-splease (AT) uk (DOT) renaultf1.com> wrote Take a look at www.boost.org for details, but beware. The whole library has grown quite big and scary over the years! Quite big, I agree with Alisdair. What's scary are the years that I didn't use it Back to top Alisdair Meredith Guest Posted: Sat Mar 26, 2005 8:40 pm    Post subject: Re: Vector of TPanels? Rory Walsh wrote: Quote: Thanks for the pointers, pardon the pun! I'll keep grafting away at it. It's making more sense now. I can't believe that I have never used vectors before? Cheers, Rory. I thoroughly recommend this book: http://www.josuttis.com/libbook/ as the easiest way of learning and appreciating the C++ Standard Library. Getting your head around separate containers, iterators and algorithms takes a little getting used to, and it a bit of a chicken-and-egg situation. Until you get a feel for all 3, you will not understand any of them! Nico's book introduced them well, along with several easy to use motivating examples. I can't recommend it highly enough. AlisdairM(TeamB) Back to top Rory Walsh Guest Posted: Sat Mar 26, 2005 9:41 pm    Post subject: Re: Vector of TPanels? Quote: m_points.push_back( new TPanel(Image1) ); This expands the vector by 1 element, and puts the panel in it. I had also been setting the attributes of each TPanel as I created them, for example I was doing this: m_Points[incr] = new TPanel(Image1); m_Points[incr]->Parent = Panel1; m_Points[incr]->Left = 1; m_Points[incr]->Top = Image1->Height-8; m_Points[incr]->Width = 10; m_Points[incr]->Height = 10; m_Points[incr]->BevelInner = true; If I now do this: m_points.push_back( new TPanel(Image1) ); m_Points[incr]->Parent = Panel1; m_Points[incr]->Left = 1; m_Points[incr]->Top = Image1->Height-8; m_Points[incr]->Width = 10; m_Points[incr]->Height = 10; m_Points[incr]->BevelInner = true; I get some strange errors. Originating from the line where I specify the parent? Ideally I would prefer to use method you suggested as I can create a leftmost and rightmost panel and then insert the rest between them. Otherwise there is not much difference between this and an array? Any ideas? Back to top Rory Walsh Guest Posted: Sat Mar 26, 2005 10:21 pm    Post subject: Re: Vector of TPanels? Actually it compiles alright but I get a fatal exception when I create a new panel dynamically. Quote: m_points.push_back( new TPanel(Image1) ); This expands the vector by 1 element, and puts the panel in it. I had also been setting the attributes of each TPanel as I created them, for example I was doing this: m_Points[incr] = new TPanel(Image1); m_Points[incr]->Parent = Panel1; m_Points[incr]->Left = 1; m_Points[incr]->Top = Image1->Height-8; m_Points[incr]->Width = 10; m_Points[incr]->Height = 10; m_Points[incr]->BevelInner = true; If I now do this: m_points.push_back( new TPanel(Image1) ); m_Points[incr]->Parent = Panel1; m_Points[incr]->Left = 1; m_Points[incr]->Top = Image1->Height-8; m_Points[incr]->Width = 10; m_Points[incr]->Height = 10; m_Points[incr]->BevelInner = true; I get some strange errors. Originating from the line where I specify the parent? Ideally I would prefer to use method you suggested as I can create a leftmost and rightmost panel and then insert the rest between them. Otherwise there is not much difference between this and an array? Any ideas? Back to top Rory Walsh Guest Posted: Sat Mar 26, 2005 11:31 pm    Post subject: Re: Vector of TPanels? I seem to be going round in circles here. If I explain what I am trying to do perhaps someone can tell me if I am going about it the right way? First I create a simple line going from the bottom right corner of a canvas to the bottom left corner of a canvas. Each time I click on the canvas a new panel will be created and the line will connect from the two corners to the panel position. If I create another panel somewhere on the canvas between an existing panel and the corner a line will connect between them. A little like an elastic on a notice board. My idea was to create a vector of panels and each time I create a new panel between any other two it would simple jump into the vector list between the other two panel. This just makes drawing the lines a whole lot easier. Is a vector list the best way to do this? And can I insert panels anywhere into a vector list? It all going okay until I try to delete the panels by right-clicking! Cheers, Rory. Rory Walsh wrote: Quote: Actually it compiles alright but I get a fatal exception when I create a new panel dynamically. m_points.push_back( new TPanel(Image1) ); This expands the vector by 1 element, and puts the panel in it. I had also been setting the attributes of each TPanel as I created them, for example I was doing this: m_Points[incr] = new TPanel(Image1); m_Points[incr]->Parent = Panel1; m_Points[incr]->Left = 1; m_Points[incr]->Top = Image1->Height-8; m_Points[incr]->Width = 10; m_Points[incr]->Height = 10; m_Points[incr]->BevelInner = true; If I now do this: m_points.push_back( new TPanel(Image1) ); m_Points[incr]->Parent = Panel1; m_Points[incr]->Left = 1; m_Points[incr]->Top = Image1->Height-8; m_Points[incr]->Width = 10; m_Points[incr]->Height = 10; m_Points[incr]->BevelInner = true; I get some strange errors. Originating from the line where I specify the parent? Ideally I would prefer to use method you suggested as I can create a leftmost and rightmost panel and then insert the rest between them. Otherwise there is not much difference between this and an array? Any ideas? Back to top Duane Hebert Guest Posted: Sun Mar 27, 2005 1:14 am    Post subject: Re: Vector of TPanels? "Rory Walsh" <rorywalsh (AT) ear (DOT) ie> wrote Quote: I seem to be going round in circles here. If I explain what I am trying to do perhaps someone can tell me if I am going about it the right way? First I create a simple line going from the bottom right corner of a canvas to the bottom left corner of a canvas. Each time I click on the canvas a new panel will be created and the line will connect from the two corners to the panel position. If I create another panel somewhere on the canvas between an existing panel and the corner a line will connect between them. A little like an elastic on a notice board. My idea was to create a vector of panels and each time I create a new panel between any other two it would simple jump into the vector list between the other two panel. This just makes drawing the lines a whole lot easier. Is a vector list the best way to do this? And can I insert panels anywhere into a vector list? It all going okay until I try to delete the panels by right-clicking! Cheers, Rory. There's no vector list. You seem to be trying to use a std::vector. A vector is similar to a variable sized array. It can be accessed by iterator or index. In order to allow access by index, the data it holds must be ordered. If you want to add to the end of a vector, it works well. If you want to insert into the middle, it has to copy everything from the middle to the end and append after the insert. A std::list is a list. It can't be accessed via an iterator. It has to be traversed. It doesn't have to maintain sequential members so inserting/deleting from the middle is less expensive. You can achieve what you want with a vector but you have to be aware of the complexity. If you're just storing pointers, you could init the vector with some number of null pointers. When you build your panel, find that index and create a new panel. When it goes away, find the index and delete the pointer, then set it to null. In your initial example, you seemed to be trying to use the index but you weren't filling it up with null pointers first. Allisdair tried to point this out to you, then suggested a better way would be to use push_back. This would be my suggestion as well but you would need to still find the index in the vector to delete it. I don't remember if TPanel has a tag property but you could use that to store it. Your last post was asking about how to use the panel after pushing it into the vector. You can get the last member with back(). You can get it's index by size() - 1. Look at the list of members for std::vector. You could also create the pointer first and then push it into the vector after you set everything. You could derive a class from your panel, add a constructor that does everything that you want like setting the parent etc. It's hard to say which is best for you. Keep posting questions when you get stuck, but I would suggest some reading as well. HTH Back to top Duane Hebert Guest Posted: Sun Mar 27, 2005 2:24 am    Post subject: Re: Vector of TPanels? "Duane Hebert" <spoo (AT) flarn2 (DOT) com> wrote Quote: A std::list is a list. It can't be accessed via an iterator. It has to this of course should say via an index. Back to top Rory Walsh Guest Posted: Mon Mar 28, 2005 11:07 am    Post subject: Re: Vector of TPanels? Cheers, between your help and the info I have found on the web its becoming clearer(albeit slowly!). Following your last post I was able to achieve exactly what I wanted to do(thanks), apart from one thing. I want to use the 'insert' member function of vector. I tried the following: m_Points.insert(m_Points.size()-5, new TPanel(Image1)); where "m_Points.size()-5" is the position I want to place the new TPanel. I get the error: [C++ Error] Unit1.cpp(100): E2285 Could not find a match for '_STL::vector<TPanel *,_STL::allocator::insert(unsigned int,undefined)' The tests I ran with an integer vector worked fine, for example scores.insert(scores.begin()-5, 540); With regards your previous post I also changed my code so now in the Form constructor I filled the panel vector with NULL pointers. Cheers, Rory. Duane Hebert wrote: Quote: "Duane Hebert" <spoo (AT) flarn2 (DOT) com> wrote A std::list is a list. It can't be accessed via an iterator. It has to this of course should say via an index. Back to top Duane Hebert Guest Posted: Mon Mar 28, 2005 12:08 pm    Post subject: Re: Vector of TPanels? "Rory Walsh" <rorywalsh (AT) ear (DOT) ie> wrote Quote: Cheers, between your help and the info I have found on the web its becoming clearer(albeit slowly!). Following your last post I was able to achieve exactly what I wanted to do(thanks), apart from one thing. I want to use the 'insert' member function of vector. I tried the following: m_Points.insert(m_Points.size()-5, new TPanel(Image1)); where "m_Points.size()-5" is the position I want to place the new TPanel. I get the error: [C++ Error] Unit1.cpp(100): E2285 Could not find a match for '_STL::vector<TPanel *,_STL::allocator::insert(unsigned int,undefined)' The tests I ran with an integer vector worked fine, for example scores.insert(scores.begin()-5, 540); In the second case, you're using an iterator. In the first, you're using an index. Have you tried using an offset from begin() for your table insert? From dinkumware.com c++ reference: vector::insert iterator insert(iterator where, const Ty& val); void insert(iterator where, size_type count, const Ty& val); template<class InIt> void insert(iterator where, InIt first, InIt last); Back to top Duane Hebert Guest Posted: Mon Mar 28, 2005 12:50 pm    Post subject: Re: Vector of TPanels? "Duane Hebert" <spoo (AT) flarn2 (DOT) com> wrote Quote: "Rory Walsh" <rorywalsh (AT) ear (DOT) ie> wrote Quote: scores.insert(scores.begin()-5, 540); I just noticed the -5 here. Are you sure this is doing what you expect? If you have some max size of tables, why not just build that to begin with with 0 pointers and create or delete them as needed. It may be simpler than dealing with insert/delete. Also, if I was trying this I would probably start with a std::vector<boost::shared_ptr and use reset() to hide show the panels. Though using standard containers with VCL objects may take some extra care when dealing with owners and parents being destroyed. Good luck. 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