C++ :: The Proper Way To Do A Vector Of Objects
Oct 20, 2014
I've been really busy but managed to get in enough down time to learn somewhat decent info about vectors. Anyways originally my program created a dynamic array of pointers to class objects and I came across a few problems because of this. Apparently an array of pointers is now outta of the question and I will now be switching to a vector of objects instead.
Why I want a list of objects instead of pointers this little comment should clear things up.
tiles[i]->show() dereferences tiles[i] (i.e. accesses whatever it points at) before calling the show() method.
That is undefined behaviour. Once undefined behaviour occurs, there is no recovery, and there is nothing the show() method (or any subsequently called function for that matter) can do to recover (short of invoking their own forms of undefined behaviour - compiler specific hacks, etc).
Even if the show() method initialises the object correctly, it cannot change the pointer tiles[i] which is in a different scope (within main()).
What I'm trying to do is create a vector of already intialized objects so that I can use a conditional statement of every single element to properly layer my games art resources. This should also automatically fix a mild unrelated collision dectection problem too but first thing first layering.
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Nov 10, 2013
here's the problem. I want to delete the objects within a vector, although I'm not sure whether I should clear the vector afterwards. Is it really necessary?
Code:
for (i = 0; i < allSales.size(); i++)
delete allSales[i];
allSales.clear(); //Is this step necessary?
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Oct 31, 2014
I have two classes, Parent and Child, where Parent contains a vector that is used to store instances of Child. When I create an instance of Parent, three instances of Child are also created in Parent's constructor and stored in the vector. I understand that push_back() creates a shallow copy of each Child instance and that Child's destructor is called each time the loop (inside Parent's constructor) iterates. The problem is that because Child's destructor is called each time the local variable child goes out of scope, the memory previously allocated in Child's constructor is destroyed and when Child's destructor is called again later on in the program to get rid of the copy stored in vector, the program crashes. I can fix this by overriding the default copy function or by storing pointers to objects instead of copies of objects. I don't really need to use vectors in this case since I always have three children in one parent but I'm doing this as a learning exercise and would prefer to use vectors.
#include <iostream>
#include <vector>
class Child {
public:
Child() {
std::cout << "child constructor called" << std::endl;
[Code] .....
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Mar 16, 2013
So I'm trying to store class objects in a vector:
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
[Code]....
1. Am I storing it correctly?
2. How would I access the stored data, say, if I wanted to compare it to other stored data or COUT it?
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Feb 11, 2012
I'm implementing kruskal's algorithm and ran into some troubles compiling. I need to sort a vector of objects by value. Here is my code and the error I'm getting.
Code:
These are the two functions in graph.cpp (there are more but are unrelated)
#include <vector>
#include <algorithm>
#include <iostream>
using namespace std;
#include "graph.h"
#include "edge.h"
using std::vector;
void graph::sort_edgesArray() {
[code].....
//This is the error I'm getting.
graph.cpp: In member function "void graph::sort_edgesArray()":
graph.cpp:39:33: error: no matching function for call to sort
(std::vector<edge>::iterator&, std::vector<edge>::iterator&, <unresolved overloaded function type>)
/usr/include/c++/4.5/bits/stl_algo.h:5236:18: note: candidate is:
void std::sort(_RAIter, _RAIter, _Compare)
[with _RAIter = __gnu_cxx::__normal_iterator<edge*, std::vector<edge> >, _Compare = bool (graph::*)(edge&, edge&)]
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Feb 23, 2014
I'm working on a code for ascertaining the minimum penalty of an assignment problem. The basic complication of my code is this: I have a vector of objects of a custom struct. The struct has a member, which is an integer. I need to keep the vector sorted according to that member, even when objects are added to or deleted from the vector. To illustrate the problem, I'll give an example.
Code:
typedef struct examplestruct{int i;
char c;
...} es;
int function(void)
{vector<es> ObjectTable;
//insert an object so that the vector remains sorted according to i
insertobject( newobject, &ObjectTable);
//deleting the top element of the vector
deleteobject(&ObjectTable);
return 0;}
I have tried to do it using bubblesort. But it's too slow. How to make a heap out of it.
The detailed premises of the problem is this: There are a number of jobs, and with each job a completion time and a cost coefficient. We are to ascertain the optimal sequence of jobs for which the penalty is minimum. Now, suppose we are given jobs A, B, C, D and E. We find out the lower bound of penalties for all the jobs.
Suppose we find B has the lowest penalty. Then we find out the lower bound of penalties for BA, BC, BD and BE. We continue this until we have the best value and a complete sequence. The way I have implemented this in a code: I have created two structs. One is Job, with the completion time and cost coefficient as members. The other is Node. Nodes have a Job Array and a Penalty as members. Now, we have a vector of Nodes which we need to keep sorted according to the penalty. We need to insert new Nodes and delete the expanded Nodes.
I have included my code. The pushInTable function inserts the new Nodes in a sorted vector. But it slows down remarkably when we give more than 20 jobs as input.
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Mar 22, 2013
For a beginners C++ lab, I have a base class Employee and two derived classes HourlyEmployee and SalaryEmployee. In main, I have a vector defined as vector <Employee *> VEmp; It's then passed to a function to get the input, which works fine. But what I'm struggling with is another function with the header "printList(const vector <Employee *> & Ve)". It's supposed to loop through the vector and call the appropriate printPay function, which is a seperate print function inside each derived class. How do I loop through the vector and print it out? I was trying to do a for loop and something like "Ve[i].printPay();", but that doesn't work. So how would I do it?
Here's some snippets of the relevant code.
class Employee {
....
virtual void printPay() = 0;
};
class HourlyEmployee : public Employee {
[Code] ....
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Jan 28, 2015
I'm working on collision detection for a game in SFML. I successfully designed a Spatial Partition grid to speed up the collision test, in the following of this tutorial: [URL] ....
But now I have an issue with one aspect of it: Going through a vector of objects and testing all the OTHER objects in the vector against said object. The author puts it into psueudocode here:
For each tick of the clock
For every object in the game
Get all the other objects in the same grid square
For each other object in the same grid square
I have trouble with the last line, because in iterating through a vector I am not sure how to skip over the current object. Here is my own code (a couple of sysntax errors but this is a c++ question not an SFML question):
//for every moveable object
for(int i = 0; i < rects_.size(); i++){
std::vector<sf::RectangleShape> posibleObjects_; //this will be a vector of WorldObjects in a real game
//for every object in that object's gridsquare
for(int j = 0; j < rects_.size(); j++){
if(rects_[i].intersects(rects_[j])){
//collision
} } }
The problem is, a collision will always be reported because somewhere in the vector the object will eventually check against itself which is always a true collision. What is the correct way to do this?
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May 1, 2013
I have a vector of Car* objects - vector<Car*> cars
Each object in the vector has an integer attribute called passengers, which can be returned using the function getPassengers().
How do I sort the vector by the objects' passenger int? I know I need to use sort() and presumably a comparison function but I'm not quite sure how.
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Nov 5, 2014
Im creating a program for a race. The Race class has a vector of results and each element of that vector is a pointer to a result. The Result class has a Time and a pointer to a Participant. So in each race there are various results and it is a result for each participant.The Time is a class that has hours, minutes and seconds. How can I sort the vector of results from the result of the participant with the fastest time to the result of the participant with the slowest time?My code is like this:
//.h file:
class Time {
unsigned int hours;
unsigned int minutes;
unsigned int seconds;
[code]....
What am I missing to get my code to work?
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May 9, 2013
I have a pointer to a vector of objects, each object has an array and a couple of strings. how to access the data in the objects via the pointer.
Best tree::chooseSplit(vector <pgm> *ptr)
{
Best splits;
cout<<ptr[1].filePath; //not working!!!
}
filepath is a string in the pgm object. i also need to be able to access elements in an array that also exists in pgm.
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Dec 9, 2013
I'm having the same problem : [URL] .....
Though, my vector isn't one of int, it is a vector of objects from another class and NetBeans won't compile it.
#include <cstdlib>
#include<vector>
#include <string>
#include<iostream>
using namespace std;
class estoque{
[Code] .....
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Nov 5, 2014
Im creating a program for a race. The Race class has a vector of results and each element of that vector is a pointer to a result. The Result class has a Time and a pointer to a Participant. So in each race there are various results and it is a result for each participant. The Time is a class that has hours, minutes and seconds. How can I sort the vector of results from the result of the participant with the fastest time to the result of the participant with the slowest time?
Im getting some errors in my code. I put the error as comments in the code. Each error is after the line where it occurs. My code is like this:
//.h file:
class Time
{
unsigned int hours;
[Code]....
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Nov 2, 2014
I've a vector of objects that I can get my float value from by accessing it through a method.It's not a pointer of vector of objects though.
Meaning it's something like vector[i].getFloatValue().
However,how do I sort the float values by descending order since I access it through a method?
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Jun 6, 2012
I have a hierarchy of Actions (NonMovingActions and MovinActions each with sub-hierarchies). Actions class has an abstract function.
Code:
class Action {
public:
Action(Agent& agent, ...):agent(agent),..{}
virtual ~Action(void);
virtual bool run()=0;
[Code]...
It appears that C++ does not allow this (in Java it was possible). Compiler objects that Action class is abstract (and cannot be instantiated?!)
Code: error C2259: 'Action' : cannot instantiate abstract class
1- May I know what do I not understand here? We cannot refer to sub-class instances with a reference of parent class type?
2- Should I use vector of pointers instead or what?
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Feb 27, 2014
class A; //forward defined in class B.h
class B
{
private:
[Code]....
I get error message forward Declaration of class A;
What is going on here. Is there a way I could initialize all the vectors of type B to be set to NULL in the constructor?
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May 16, 2013
Say I have a vector of objects and I want to return an object based on a pair of strings. The strings can be in either order Ie; A B==B A.
In general, what do you think is the best way to do this?
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Apr 18, 2013
I am having a problem with a program. I have a bunch of classes all derived from the same base class. I want to loop through a vector of objects, calling a function in each. The problem is that it doesn't matter which class the objects are, only the function defined in the base class is called.
I simplified the code as far as possible to replicate the problem. As you see, I would like a mix of numbers 1,2,3 as the output, however using the vector the only number output is 1. Here is a copy of the output by the way:
base->num() : 1
a->num() : 2
b->num() : 3
(*it)->num() : 1
(*it)->num() : 1
(*it)->num() : 1
I suspect this is the "slice" problem, because the vector is defined with pointers to the base class so it uses the base class functions? The question is how to get around it? How can I loop through a vector of objects sharing the same base class but calling each by their correct member functions?
Code:
#include <iostream>
#include <vector>
class Base {
public:
int num() { return 1;}
[Code] .....
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Mar 5, 2013
I need manipulating a set of containers. I created a vector that contained vectors of objects:
std::vector< std::vector<Terrain> > mapArray(num1, std::vector<Terrain>(num2));
where num1 and num2 are arbitrary numbers. and Terrain is the class of objects I'm trying to store.
I want to be able to use push_back on both the main vector and the vectors within the mapArray vector but I'm unsure of how to target the inner vectors with push_back. How to dynamically store a 2D array of objects.
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Oct 13, 2013
I just created an object who store a vector of size 7 with random numbers between 1 and 36. If i declare two objects i get different vector, but running many times the program i always get the same vectors . For example, if i declare one object, even if i run any time the program, i always get the same numbers.
I am using the function
num= rand()%36+1,
wasn't it supposed to generate randoms numbers?
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Dec 10, 2014
I have a small class and a vector to hold the objects.
Code:
class result_holder {
public:
// initialize class members
[Code]....
The purpose is to keep results and be able to sort the results on row_value while keeping the id and name values in registration with the row_value. I am running allot of tests and keeping the top n results. The idea is to sort the vector so that I can just examine the object in the last element to see if it should be replaced by a better result.
I know that this kind of thing is often done with an overloaded operator or a functor, but I am a bit out of my depth with that, especially determining what class variable will be used for the sort. sorting the above objects on the row_value variable?
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Feb 10, 2015
Using SFML, I had a Board class which held multiple vectors of all of my object types in the game, and then it also held a vector of pointers to the memory addresses of these object instances, like this
class Board{
//...
std::vector<AbstractObject*> GetAllLevelObjects(){ return allLevelObjects; }
//so these are used to hold my object instances for each level
[Code]....
When looping through this vector and drawing the sprites of the objects, I get the runtime error 0xC0000005: Access violation reading location 0x00277000. I solved this error by storing the vector of pointers in the class that holds my Board instance, but I'm wondering why only this solution worked? Why couldn't I just have my vector of pointers in the same class that the instances of those objects were in?
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Mar 6, 2014
Overview of problem : I am using std::vector to hold objects of Subject. Now this vector contains lots of objects( with lots I mean 10-20 objects at max) . These objects have string member values like category and sub_category. Both category and sub_category can have string which can be same of other objects's sub_category & category.
Issue: Now I want my std::vector to have only those objects whose's sub_category are unique. If category is not unique that's not a problem .
Secondly if we found 2 objects having same sub_category then we have to delete one of them from the vector. we will delete it based on some rules example
Rules for deleting are if
i) instance of Subject ->category = " Land " OR if category = "Jungle" then delete other duplicate object ,
ii) if above condition doesn't match then delete either of them.
I am wondering , how would I compare the sub-items from the vector . For example. I have class say Subject
class Subject {
public :
// some constructors,
// functions to get ., set category and sub category
std::String get_sub_category()
std::string get_category();
private:
std::string category;
std::string sub_category;
}
I have vector which stores object of Subjects. Example : vector<Subject> copy_vector;
Now what I want is to delete the object from vector that has same sub_category I am not looking for source code buT i need a starting point,? Example:
copy_vector[0] = Animal object that has sub_category Tiger
copy_vector [1] = Animal object with Lion as sub category
copy_vector[2] = Forest object with sub_category Tiger
What I want is to based on some conditions(which I can do ) remove either Forest or Animal object containing Tiger. But for that how would I do comparison? I have written the function and have checked it.
std::vector< Subject >copy_vector;
// copy_vector contains all the objects of Subject with redundant sub_category
for( std::vector< Subject >::iterator ii = copy_vector.begin() ; ii != copy_vector.end() ; ++ii ) {
sub_category = ii->get_sub_category();
[code] ....
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May 23, 2014
I'm implementing an normal_distribution to select objects on a vector. The thing is I can't use values greater then 1 or less then -1. Here is what could be done:
gausx=gaus_distributionx(generator);
while((gausx>1) || (gausx<-1))
gausx=gaus_distributionx(generator);
The question is if the distribution would loose it's power to be a normal distribution, because some of the gerated numbers wouldn't be used. Any way to set ranges for the distribution?
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Mar 6, 2014
I am trying to use std::sort to sort a vector of complex objects using a custom function. However, it keeps erroring "Unresolved overloaded function type".
encounter::encounter(){
// ... cut
std::sort (allpeople.begin(), allpeople.end(), sortByInit);}
bool encounter::sortByInit (character& a, character& b) {
if (a.getinit () == b.getinit ()) {
[Code] ....
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Apr 11, 2014
I have a class called Question:
#include <string>
#include <vector>
using namespace std;
class Question {
string title;
vector<Thing*> posAns;
vector<Thing*> negAns;
[Code] ....
error: no instance of overloaded function 'std::vector::push_back()' matches the arguments list
argument types are (const Thing *)
object type is: std:: vector<Thing *, std::allocator<Thing *>>
So it cannot be constant, what if I just leave it non-constant? Will it be safe?
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