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  • How to change a particular element of a C++ STL vector

    - by cambr
    vector<int> l; for(int i=1;i<=10;i++){ l.push_back(i); } Now, for example, how do I change the 5th element of the vector to -1? I tried l.assign(4, -1); It is not behaving as expected. None of the other vector methods seem to fit. I have used vector as I need random access functionality in my code (using l.at(i)).

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  • lambda+for_each+delete on STL containers

    - by rubenvb
    I'm trying to get a simple delete every pointer in my vector/list/... function written with an ultra cool lambda function. Mind you, I don't know c**p about those things :) template <typename T> void delete_clear(T const& cont) { for_each(T.begin(), T.end(), [](???){ ???->delete() } ); T.clear(); } I have no clue what to fill in for the ???'s. Any help is greatly appreciated!

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  • C++ STL: Trouble with string iterators

    - by Rosarch
    I'm making a simple command line Hangman game. void Hangman::printStatus() { cout << "Lives remaining: " << livesRemaining << endl; cout << getFormattedAnswer() << endl; } string Hangman::getFormattedAnswer() { return getFormattedAnswerFrom(correctAnswer.begin(), correctAnswer.end()); } string Hangman::getFormattedAnswerFrom(string::const_iterator begin, string::const_iterator end) { return begin == end? "" : displayChar(*begin) + getFormattedAnswerFrom(++begin, end); } char Hangman::displayChar(const char c) { return c; } (Eventually, I'll change this so displayChar() displays a - or a character if the user has guessed it, but for simplicity now I'm just returning everything.) When I build and run this from VS 2010, I get a popup box: Debug Assertion Failed! xstring Line: 78 Expression: string iterator not dereferenceable What am I doing wrong?

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  • C++ STL 101: Overload function causes build error

    - by Sidjal
    Trivial code that works if I do not overload myfunc. void myfunc(int i) { std::cout << "calling myfunc with arg " << i << std::endl; } void myfunc(std::string s) { std::cout << "calling myfunc with arg " << s << std::endl; } void testalgos() { std::vector<int> v; v.push_back(1); v.push_back(2); std::vector<std::string> s; s.push_back("one"); s.push_back("two"); std::for_each( v.begin(), v.end(), myfunc); std::for_each( s.begin(), s.end(), myfunc); return; } int _tmain(int argc, _TCHAR* argv[]) { std::cout << "Hello World" << std::endl; testalgos(); return 0; } The following build errors repeat for both for_each calls. error C2914: 'std::for_each' : cannot deduce template argument as function argument is ambiguous error C2784: '_Fn1 std::for_each(_InIt,_InIt,_Fn1)' : could not deduce template argument for '_InIt' from 'std::_Vector_iterator<_Ty,_Alloc'. It does work if I do not overload myfunc.Can someone explain what is happening here. TIA

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  • C++ STL: Array vs Vector: Raw element accessing performance

    - by oh boy
    I'm building an interpreter and as I'm aiming for raw speed this time, every clock cycle matters for me in this (raw) case. Do you have any experience or information what of the both is faster: Vector or Array? All what matters is the speed I can access an element (opcode receiving), I don't care about inserting, allocation, sorting, etc. I'm going to lean myself out of the window now and say: Arrays are at least a bit faster than vectors in terms of accessing an element i. It seems really logical for me. With vectors you have all those security and controlling overhead which doesn't exist for arrays. (Why) Am I wrong? No, I can't ignore the performance difference - even if it is so small - I have already optimized and minimized every other part of the VM which executes the opcodes :)

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  • Need help with map (c++, STL)

    - by Mike Dooley
    Hi folks! Actually I'm new to C++. I tried something out (actually the map container) but it doesn't work the way I assumed it will... Before posting my code, I will explain it shortly. I created 3 classes: ClassA ClassDerivedA ClassAnotherDerivedA The two last ones are derived from "ClassA". Further I created a map: map<string,ClassA> test_map; I put some objects (from Type ClassDerivedA and ClassAnotherDerivedA) into the map. Keep in mind: the mapped value is from type "ClassA". This will only work because of Polymorphism. Finally I created an iterator which runs over my map and compares the user input with my keys in the map. If they match, it will call a specific method called "printOutput". And there is the Problem: Although i declared "printOutput" as "virtual" the only method called is the one from my base class, but why? and here is the code: #include <iostream> #include <map> using namespace std; class ClassA { public: virtual void printOutput() { cout << "ClassA" << endl; } }; class ClassDerivedA : public ClassA { public: void printOutput() { cout << "ClassDerivedA" << endl; } }; class ClassAnotherDerivedA: public ClassA { public: void printOutput() { cout << "ClassAnotherDerivedA" << endl; } }; int main() { ClassDerivedA class_derived_a; ClassAnotherDerivedA class_another_a; map<string,ClassA> test_map; test_map.insert(pair<string,ClassA>("deriveda", class_derived_a)); test_map.insert(pair<string,ClassA>("anothera", class_another_a)); string s; while( cin >> s ) { if( s != "quit" ) { map<string,ClassA>::iterator it = test_map.find(s); if(it != test_map.end()) it->second.printOutput(); } else break; } } Blockquote

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  • C++ STL list vs set

    - by mokaschitta
    Hi, what of those two is faster for random insertions and deletions? I guess list, having the values as the keys as it is with sets seems to be attractive too though. Is performance similar for iterating over the whole container? Thanks!

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  • [c++/STL] Selective iterator

    - by rubenvb
    FYI: no boost, yes it has this, I want to reinvent the wheel ;) Is there some form of a selective iterator (possible) in C++? What I want is to seperate strings like this: some:word{or other to a form like this: some : word { or other I can do that with two loops and find_first_of(":") and ("{") but this seems (very) inefficient to me. I thought that maybe there would be a way to create/define/write an iterator that would iterate over all these values with for_each. I fear this will have me writing a full-fledged custom way-too-complex iterator class for a std::string. So I thought maybe this would do: std::vector<size_t> list; size_t index = mystring.find(":"); while( index != std::string::npos ) { list.push_back(index); index = mystring.find(":", list.back()); } std::for_each(list.begin(), list.end(), addSpaces(mystring)); This looks messy to me, and I'm quite sure a more elegant way of doing this exists. But I can't think of it. Anyone have a bright idea? Thanks PS: I did not test the code posted, just a quick write-up of what I would try

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  • Tree Node Checked behavior on a TreeView in Compact Framework 3.5 running on Windows Mobile 6.5

    - by Hydroslide
    I have been upgrading an existing .NET Windows Mobile application to use the 3.5 version of the compact framework and to run on Windows Mobile 6.5. I have a form with a TreeView. The TreeView.Checkboxes property is set to true so that each node has a check box. This gives no trouble in all previous versions of Windows Mobile. However, in version 6.5 when you click on a check box it appears to check and then uncheck instantaneously. But it only raises the AfterCheck event once. The only way I can get a check to stick is by double clicking it (which is the wrong behavior). Has anyone seen this behavior? Does anyone know of a workaround for it? I have included a simple test form. Dump this form into a Visual Studio 2008 Smart Device application targeted at Windows Mobile 6 to see what I mean. Public Class frmTree Inherits System.Windows.Forms.Form #Region " Windows Form Designer generated code " Public Sub New() MyBase.new() ' This call is required by the Windows Form Designer. InitializeComponent() ' Add any initialization after the InitializeComponent() call. End Sub 'Form overrides dispose to clean up the component list. <System.Diagnostics.DebuggerNonUserCode()> _ Protected Overrides Sub Dispose(ByVal disposing As Boolean) If disposing AndAlso components IsNot Nothing Then components.Dispose() End If MyBase.Dispose(disposing) End Sub 'Required by the Windows Form Designer Private components As System.ComponentModel.IContainer Friend WithEvents TreeView1 As System.Windows.Forms.TreeView Private mainMenu1 As System.Windows.Forms.MainMenu 'NOTE: The following procedure is required by the Windows Form Designer 'It can be modified using the Windows Form Designer. 'Do not modify it using the code editor. <System.Diagnostics.DebuggerStepThrough()> _ Private Sub InitializeComponent() Dim TreeNode1 As System.Windows.Forms.TreeNode = New System.Windows.Forms.TreeNode("Node0") Dim TreeNode2 As System.Windows.Forms.TreeNode = New System.Windows.Forms.TreeNode("Node2") Dim TreeNode3 As System.Windows.Forms.TreeNode = New System.Windows.Forms.TreeNode("Node3") Dim TreeNode4 As System.Windows.Forms.TreeNode = New System.Windows.Forms.TreeNode("Node4") Dim TreeNode5 As System.Windows.Forms.TreeNode = New System.Windows.Forms.TreeNode("Node1") Dim TreeNode6 As System.Windows.Forms.TreeNode = New System.Windows.Forms.TreeNode("Node5") Dim TreeNode7 As System.Windows.Forms.TreeNode = New System.Windows.Forms.TreeNode("Node6") Dim TreeNode8 As System.Windows.Forms.TreeNode = New System.Windows.Forms.TreeNode("Node7") Me.mainMenu1 = New System.Windows.Forms.MainMenu Me.TreeView1 = New System.Windows.Forms.TreeView Me.SuspendLayout() ' 'TreeView1 ' Me.TreeView1.CheckBoxes = True Me.TreeView1.Location = New System.Drawing.Point(37, 41) Me.TreeView1.Name = "TreeView1" TreeNode2.Text = "Node2" TreeNode3.Text = "Node3" TreeNode4.Text = "Node4" TreeNode1.Nodes.AddRange(New System.Windows.Forms.TreeNode() {TreeNode2, TreeNode3, TreeNode4}) TreeNode1.Text = "Node0" TreeNode6.Text = "Node5" TreeNode7.Text = "Node6" TreeNode8.Text = "Node7" TreeNode5.Nodes.AddRange(New System.Windows.Forms.TreeNode() {TreeNode6, TreeNode7, TreeNode8}) TreeNode5.Text = "Node1" Me.TreeView1.Nodes.AddRange(New System.Windows.Forms.TreeNode() {TreeNode1, TreeNode5}) Me.TreeView1.Size = New System.Drawing.Size(171, 179) Me.TreeView1.TabIndex = 0 ' 'frmTree ' Me.AutoScaleDimensions = New System.Drawing.SizeF(96.0!, 96.0!) Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Dpi Me.AutoScroll = True Me.ClientSize = New System.Drawing.Size(240, 268) Me.Controls.Add(Me.TreeView1) Me.Menu = Me.mainMenu1 Me.Name = "frmTree" Me.Text = "frmTree" Me.ResumeLayout(False) End Sub #End Region End Class

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  • Why does std queue not define a swap method specialisation

    - by Jamie Cook
    I've read that all stl containers provide a specialisation of the swap algorithm so as to avoid calling the copy constructor and two assignment operations that the default method uses. However, when I thought it would be nice to use a queue in some code I was working on I noticed that (unlike vector and deque) queue doesn't provide this method? I just decided to use a deque instead of a queue, but still I'm interested to know why this is?

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  • How to void checked exceptions in Java?

    - by deamon
    I consider checked exception for a design mistake in the Java language. They lead to leaky abstractions and a lot of clutter in the code. It seems that they force the programmer to handle exceptions early although they are in most cases better handled lately. So my question is how to avoid checked exception? My idea is to execute the actual code inside an exception translator using lambda expressions. Example: ExceptionConverter.convertToRuntimeException(() => { // do things that could throw checked exceptions here }); If for example a IOException occurs it gets rethrown as an exception with the same name but from a different class hierarchy (based on RuntimeException). This approach would effectivly remove the need to handle or declare checked exceptions. Exceptions could then be handled where and if it makes sense. Another solution would be to declare IOException throws Exception on each method. What do you think which solution is better? Do you know any better approach to avoid (suppress) checked exceptions in Java?

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  • Reversing strings in a vector using for_each and bind

    - by fmuecke
    Hi! I was wandering how it's possible to reverese strings that are contained in a vector using a single for_each command just in one "simple" line. Yea, I know it is easy with a custom functor, but I can't accept, that it can't be done using bind (at least I couldn't do it). #include <vector> #include <string> #include <algorithm> std::vector<std::string> v; v.push_back("abc"); v.push_back("12345"); std::for_each(v.begin(), v.end(), /*call std::reverse for each element*/); Edit: Thanks a lot for those funtastic solutions. However, the solution for me was not to use the tr1::bind that comes with the Visual Studio 2008 feature pack/SP1. I don't know why it does not work like expected but that's the way it is (even MS admits that it's buggy). Maybe some hotfixes will help. With boost::bind everything works like desired and is so easy (but sometimes relly messy:)). I really should have tried boost::bind in the first place...

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  • Why do programmers sometimes refer to "C++/STL" like it's a separate language?

    - by BillyONeal
    This may seem a trivial question, but it's one that's bothered me a lot lately. Why do some programmers refer to "C++/STL" like it's a different language? The STL is part of the C++ standard library -- and therefore is part of the language, "C++". It's not a separate component, and it does not live alone in the scope of things C++. Yet some continually act like it's a different language altogether. Why?

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  • Why is overloading operator&() prohibited for classes stored in STL containers?

    - by sharptooth
    Suddenly in this article ("problem 2") I see a statement that C++ Standard prohibits using STL containers for storing elemants of class if that class has an overloaded operator&(). Having overloaded operator&() can indeed be problematic, but looks like a default "address-of" operator can be used easily through a set of dirty-looking casts that are used in boost::addressof() and are believed to be portable and standard-compilant. Why is having an overloaded operator&() prohibited for classes stored in STL containers while the boost::addressof() workaround exists?

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  • C++ STL: How to iterate vector while requiring access to element and its index?

    - by Ashwin
    I frequently find myself requiring to iterate over STL vectors. While I am doing this I require access to both the vector element and its index. I used to do this as: typedef std::vector<Foo> FooVec; typedef FooVec::iterator FooVecIter; FooVec fooVec; int index = 0; for (FooVecIter i = fooVec.begin(); i != fooVec.end(); ++i, ++index) { Foo& foo = *i; if (foo.somethingIsTrue()) // True for most elements std::cout << index << ": " << foo << std::endl; } After discovering BOOST_FOREACH, I shortened this to: typedef std::vector<Foo> FooVec; FooVec fooVec; int index = -1; BOOST_FOREACH( Foo& foo, fooVec ) { ++index; if (foo.somethingIsTrue()) // True for most elements std::cout << index << ": " << foo << std::endl; } Is there a better or more elegant way to iterate over STL vectors when both reference to the vector element and its index is required? I am aware of the alternative: for (int i = 0; i < fooVec.size(); ++i) But I keep reading about how it is not a good practice to iterate over STL containers like this.

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  • how do I get all checkbox variables even if not checked from HTML to PHP?

    - by netrox
    I noticed that PHP seems to return only values of checked checkboxes. I would like to see a list of checkboxes, not just values of checked checkboxes. Is there a way to detect variables of unchecked boxes? I asked because I want to be able to update settings. For example, I have a few options that are already checked but if an user decides to uncheck an option, I need to know that unchecked value so I can update the option to be disabled.

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  • Clone a DataBound Checked List Box

    - by Buddhi Dananjaya
    Hi I have a DataBound CheckedListBox, I "check" few items on list box(source), then I need to clone it to new Checked List Box(target). It need to have all the data, with checked state. I have tried with following function. It is properly flowing through this function. But finally I can see items on target CheckedListBox but none of the items in target is checked. private void CloneCheckedListBox(CheckedListBox source, CheckedListBox target) { foreach (int checkedItemIndex in source.CheckedIndices) { target.SetItemChecked(checkedItemIndex, true); } } Edit: I have a User control which I have placed on a TabPage, on that User Control there is a "CheckedListBox", I do need to create a new TabPage with the user entered value on selected(current) TabPage(on User Control) So, what I have done is, create a new Tab Page, get a Copy of the User Control calling it's "Clone()" method. In "Clone()" method need to have CheckedListBox cloning feature. Here is my Cloning Code, which is on User Control... public SearchMain Clone() { SearchMain smClone = new SearchMain(); smClone.txtManufacturers.Text = this.txtManufacturers.Text; smClone.udPriceFrom.Value = this.udPriceFrom.Value; smClone.udPriceTo.Value = this.udPriceTo.Value; smClone.chkOld.Checked = this.chkOld.Checked; smClone.chkPrx.Checked = this.chkPrx.Checked; smClone.chkDisc.Checked = this.chkDisc.Checked; smClone.chkStock.Checked = this.chkStock.Checked; smClone.chkFirstDes.Checked = this.chkFirstDes.Checked; smClone.chkFirstPN.Checked = this.chkFirstPN.Checked; smClone.txtSuppPN.Text = this.txtSuppPN.Text; smClone.txtManuPN.Text = this.txtManuPN.Text; smClone.txtManufacturers.Text = this.txtManufacturers.Text; smClone.meDesAND.Text = this.meDesAND.Text; smClone.meDesOR.Text = this.meDesOR.Text; smClone.meDesNOT.Text = this.meDesNOT.Text; smClone.lbManufacSelected.Items.AddRange(this.lbManufacSelected.Items); smClone.lbSearchWithIn.Items.AddRange(this.lbSearchWithIn.Items); **CloneCheckedListBox(this.clbLang, smClone.clbLang);** // CloneCheckedListBox(this.clbTypes, smClone.clbTypes); return smClone; }

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  • How would I use for_each to delete every value in an STL map?

    - by stusmith
    Suppose I have a STL map where the values are pointers, and I want to delete them all. How would I represent the following code, but making use of std::for_each? I'm happy for solutions to use Boost. for( stdext::hash_map<int, Foo *>::iterator ir = myMap.begin(); ir != myMap.end(); ++ir ) { delete ir->second; // delete all the (Foo *) values. } (I've found Boost's checked_delete, but I'm not sure how to apply that to the pair<int, Foo *> that the iterator represents). (Also, for the purposes of this question, ignore the fact that storing raw pointers that need deleting in an STL container isn't very sensible).

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  • any ideas how to make checked treeview inside multiselect jqeury?

    - by B_S
    i planned to make checked treeview inside a multiselect jquery. The left side was the checked treeview, if we choose the child, the one moving to the right side was the child and the parent title, and if we choose the parent, all of the child will be moving right. I found some of the example, but they're in vb, can jqeury make something like this?

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  • Defining < for STL sort algorithm - operator overload, functor or standalone function?

    - by Andy
    I have a stl::list containing Widget class objects. They need to be sorted according to two members in the Widget class. For the sorting to work, I need to define a less-than comparator comparing two Widget objects. There seems to be a myriad of ways to do it. From what I can gather, one can either: a. Define a comparison operator overload in the class: bool Widget::operator< (const Widget &rhs) const b. Define a standalone function taking two Widgets: bool operator<(const Widget& lhs, const Widget& rhs); And then make the Widget class a friend of it: class Widget { // Various class definitions ... friend bool operator<(const Widget& lhs, const Widget& rhs); }; c. Define a functor and then include it as a parameter when calling the sort function: class Widget_Less : public binary_function<Widget, Widget, bool> { bool operator()(const Widget &lhs, const Widget& rhs) const; }; Does anybody know which method is better? In particular I am interested to know if I should do 1 or 2. I searched the book Effective STL by Scott Meyer but unfortunately it does not have anything to say about this. Thank you for your reply.

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  • Function templates for arbitrary STL containers containing arbitrary types.

    - by Chad Brewbaker
    I have an arbitrary STL container C, which contains elements of an arbitrary type T. I want to create an std::vector that has a copy of all the elements. What is the cleanest way to do this? template <typename C> void myfunction(C container){ /*Derive the type T of elements within the container*/ std::vector<T> mystack; /* Iterate over container and push_back() the elements into mystack*/ }

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