c++ - Is it possible to erase modified element from std::set? -


i need sorted collection elements can modified. safe erase element after modification? sorting key can modified.

auto it=s.find(e) modify(e) s.erase(it)

i have made tests in vs2010, , worked. think erase(it) not need search element, there no need call compare on element being erased.

it hard modify whole program remove elements before modification, why looking alternative solution.

edit: adding working sample make more clear

#include <iostream> #include <algorithm> #include <set>  template <typename t> struct ptrcmp {     bool operator()(const t* x, const t* y) const     {         return *x<*y;     } };  int main() {     std::set<int*, ptrcmp<int>> aset;     int t[]={1,2,3,4};     for(int i=0;i<4;++i)     aset.insert(&t[i]);      auto it=aset.find(&t[2]);     t[2]=5;     aset.erase(it);      for(auto it=aset.begin(); it!=aset.end(); ++it)         std::cout<<**it<<std::endl; }

in example t[2]=5; modifies value used in comparator used e.g. rebalancing tree data structure behind set container. therefore such modification not safe because balanced-tree algorithm may fail in case factual key @ node changed, therefore not match expectation tree node. erase operation trigger tree rebalancing, , how undefined behavior. modification of value used in comparator factually break balancedness of tree behind set container.


Comments

Post a Comment

Popular posts from this blog

javascript - Using jquery append to add option values into a select element not working -

i'm looking dynamically populate select element names of items stored array. for reason it's not working , i'm not sure why. html: <div class="col-md-4 col-md-offset-4"> <select class="select1"> </select> , <select class="select2"> </select> </div> note i'm using bootstrap layout. here's jquery i'm using try , populate ".select1" jquery: select: function() { $.each(state.greens, function(index, value) { $(".select1").append("<option value =' " + index + " '>" + state.greens[index].name + "</option>"); }); } note function 'select' stored within object called 'display'. state.greens name of array i'm trying access. so @ end of html page call display.select(); call function. no error messages showing in console. also, saw question: appending
Read more

Android soft keyboard reverts to default keyboard on orientation change -

i'm building android soft keyboard , can't seem fix bug - have arabic , qwerty keyboard , when rotate device on qwerty keyboard (or arabic shift), it's if program has "restarted" , becomes arabic keyboard without shift. the onsaveinstancestate(bundle savedinstancestate) not work because application not extend activity inputmethodservice . i put following in android manifest android:configchanges="keyboard|keyboardhidden|orientation" android:windowsoftinputmode="stateunchanged|adjustresize"> i tried using @override public void onconfigurationchanged(configuration newconfig) { super.onconfigurationchanged(newconfig); log.i(mydebug, "config changed " + currentkeyboard.equals(qwerty)); } however, currentkeyboard.equals(qwerty)) results false , made sure true before orientation change. any appreciated. i think applications fault. if application restarting on orientation change
Read more

Rendering JButton to get the JCheckBox behavior in a JTable by using images does not update my table -

i rendering jbutton image on simulate jcheckbox behavior. why don't let jtable render jcheckbox? because need bigger checkboxes , there's no way can resize them (as far know). so, have own table cell renderer , editor. both renders jbutton , checkbox images on them. trying change image checked image unchecked image (or vice versa) , update cell value (boolean true or false). however, reason, getcelleditorvalue() not update table. so, release mouse, value goes original one. any appreciated! lot! public class tableexample extends jframe { jscrollpane pane; jpanel panel; jtable table; object[][] data; mytablemodel tm; renderer buttoncolumn; public tableexample(object[][] data) throws ioexception { string[] columns = {"column#1", "column#2", "column#3", "column#4", "column#5", "column#6"}; this.data = data; this.setpreferredsize(new dimension(700, 500));
Read more