C++ :: Vector Of Pointers - Push Back Objects / Constant Parameters
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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Feb 9, 2015
How to output vector contents using the push_back function. My program reads in values just fine, but it does not output anything and I've been stuck on why.
here is my code:
#include <iostream>
#include <array>
#include <vector>
using namespace std;
int duplicate( vector < int > &vector1, const int value, const int counter)
[Code].....
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May 23, 2013
I have below classes
Code:
class moClassValueContainer {
public:
moClassValueContainer();
moClassValueContainer(string,int);
[Code] ....
In my main.cpp, I have blow loop
Code:
for (xml_node tnode = it->first_child(); tnode ; tnode = tnode.next_sibling()) {
Container tmpContainer(tnode);
if (tmpContainer.getType() == SINGLE) {
string t = tmpContainer.getName();
[Code] ....
I cannot push_back(t). I examined the code with debugger, t has correct string value assigned, but even after 20-30 iterations, there is no element for headerFields vector.
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Jul 31, 2013
I am trying to use push back in a 2D vector but I don't know how to. This is what I have:
vector <vector <BigInt> > matr;
for (BigInt i=0;i<rij;i++) {
for (BigInt j=0;j<kolom-1;j++) {
matr.push_back().push_back((i+1)^(pow-j));
}
}
I quickly invented something but that doesn't work obviously. it should be equivalent to this: (the only problem in the code below is that those indexes don't exist yet that's why I need push_back())
for (BigInt i=0;i<rij;i++) {
for (BigInt j=0;j<kolom-1;j++) {
matr[int(i)][int(j)]=(i+1)^(pow-j);
}
}
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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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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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May 8, 2014
How to now randomize the answer order within this code ? I only included the relevant piece of code of the task in question.
questions.push_back(
"Question [1]"
" "
"What port does HTTPS use ? "
"1. 25 "
"2. 443 "
"3. 23 ");
answers.push_back("2");
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Mar 28, 2014
How to avoid using Backspace character with push_back? I'm making a software as an ATM, so when the user try to enter the password the user only sees *******, but when trying to delete it doesn't delete a character. It just adds a new one. Here's my code:
string password2 = "";
cout << "PASSWORD: ";
ch = _getch();
while(ch != 13) //character 13 is enter {
password2.push_back(ch);
cout << '*';
ch = _getch();
}
And also, I try to use pop_back(); but it doesn't work either.
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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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Apr 20, 2013
How can push data into the vector <list<Edge>> adjList? adjList[n].push_back (e);//gives error.
struct Edge {
int from_node_number;
int to_node_number;
int weight;
};
vector <list<Edge>> adjList;
Edge e;
for (int n=0; n< graph.size(); n++)
adjList[n].push_back (e);
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Apr 9, 2013
I am creating code for a group project in my class. All my group members made a header file with an object in it with their functions. One of the functions in my partner's code uses a data member of mine in the function, so she has the function parameter a object of my object. (This isn't the code but for example)
class B {
friend class A;
void displayAthing(A object) {
cout<<object.thing<<endl;
}
I have this when I call the function in the cpp file
int main() {
A object;
B b;
b.displayAthing(object);
return 0;
}
However, when I compile, it gives me an error that the function does not take 1 arguments.
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Feb 10, 2014
I have a standard linked list in template format (with T being the typename) with the following relevant insertion operators:
bool PushFront (const T& t); // Insert t at front of list
bool PushBack (const T& t); // Insert t at back of list
I want to build a list of pointers to objects (we'll call them objects of class Box for simplicity) that is member data for a parent class (we'll call that class Warehouse). However, I want to have a constant Box....const Box INVISIBLE_BOX = Box(); that represents a nonexistent Box. However, I cannot use either
PushFront(&INVISIBLE_BOX)
or
PushBack(&INVISIBLE_BOX)
to add INVISIBLE_BOX to the list of boxes without getting an invalid conversion error invalid conversion from âconst warehouse::Box*â to âwarehouse:: Box*â [-fpermissive]
What can I do to make it take a constant Box? I am using g++ to compile these files.
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Oct 24, 2013
I have been experimenting with variadic templates with the aim of caching a call to a class method by storing away the object pointer, method pointer and parameters. I've actually had some reasonable success but have now hit a stumbling block. I now wish to wrap my parameters in a simple template class when I cache them. My success is as follows:
Using variadic template functions to store these pointers and paremeters;
I'm able to pass a method pointer and unwrapped parametersI'm able to pass wrapped parameters on their own.I'm NOT able to pass a method pointer and wrapped parameters I set up a little prototype project to demonstrate the issue and added comments above the function calls to indicate the compilation results. Here is the code:
Code:
#include "stdafx.h"
//////////////////////////////////////////////////
// Basic class with a simple method
//////////////////////////////////////////////////
class MyClass {
public:
char Method( int i, float f ) {
return 'A';
[code]....
But I'm convinced it should take three arguments, the method pointer and two wrapped parameters. Visual studio even suggested it should as shown below:
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Feb 15, 2012
I'm able to convert an integer to a vector<unsigned char> and back. However, when I try to use a nearly identical function designed for the long long data type, the last byte or two is broken.
Program code:
long long num = 9223372036854775551LL;
cout << "Before: " << num << endl;
vector<unsigned char> data = getBytes(num);
num = getLongLong(data);
cout << "After: " << num << endl;
Code for converting between vector<unsigned char> and long long:
Code:
vector<unsigned char> getBytes(long long value) {
int bytes = sizeof(value);
vector<unsigned char> data(bytes);
for (int i = 0; i < bytes; i++)
data.at(i) = (unsigned char)( value >> ((bytes-i)*8) );
[Code] ....
Output:
Code:
Before: 9223372036854775807
After: 9223372036854775552
Is there something special about long long that would prevent this from working? This problem doesn't happen with int.
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Mar 21, 2014
I need to iterate through a vector in a const function, and, as my function is called very often, to get more performances I need my iterator to be declared somewhere else than the function, so it doesn't have to get deleted and recreated over and over again. So here is my code:
class Shop {
public:
//methods
virtual void draw(sf::RenderTarget &target, sf::RenderStates states) const{
[Code] ....
Seems great? Well no. I actually get an error on the "for" line.
It tells me : "You can't use '=' here" and "You can't use the ++ operator here"
The thing is, if I actually declare my iterator in the loop, the compiler stops giving me warnings, but, as I said, I really want to avoid doing that.
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Jun 6, 2013
I am using OpenCV to read and manipulate a set of images, which I need to store in an array to work with them. Here is a snippet of the code:
#define MAX_IMAGES 8
typedef Mat* MatPtr;
int main(int argc, char** argv) {
char imageName[] = "./res/imageX.tiff";
MatPtr datacube[MAX_IMAGES];
[code].....
I have an array of pointers to Mat objects (an OpenCV class used to hold info and data about an image), which I will use to store the images. The function imread reads an image and returns a Mat object loaded with the relevant data about the image.However, this gives me a nice segfault when the assignment takes place. Of course, I can swap it with the following code, but since I'm working with big images (2048x2048 and upwards), it's really inefficient:
for(unsigned int i = 0; i < MAX_IMAGES; i++) {
imageName[11] = 49 + i;
datacube[i] = new Mat(imread(imageName, -1));
}
Is there any way to do this elegantly and without much hassle?Again, excuse my rustiness and anything completely stupid I might have said. It's been a long time since I worked with C++. Managed to circumvent the problem by using a STD vector instead of an array. I'd still like to know the answer to this riddle...
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Sep 27, 2013
I've created an Array of pointers to objects using:
Person ** A = new person * [arraysize];
When I intend to access a specific person do I have to do this? :
something = A->[i];
and when I want a specific object within my struct do I have to do this? :
something_else = A->[i]->random_int;
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Dec 5, 2013
my code:
int OKCount=0;
int WaitingCount=0;
int ReservationCount=0;
Flight::Flight(int capacity, int waitingMax) {
seats=capacity;
[code].....
reservations is a data member in the class flight as:
Reservation **reservations;
OKReservation is a derived class and its abstract base class is Reservation.
My problem is that the reservations array loses its value in other function
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Apr 14, 2014
I have a data structure defined up here called this:
typedef list <classSpec*> ClassSpecList;
I'm trying to add stuff into the list here based on functions that return certain values of that match the same data type. In one function, I have a list pointer object defined here and I have another statement that calls a function.
ClassSpecList *answer = 0;
classSpec *thisanswer = parseClass(br);
Basically I'm trying to add the results of what thisanswer returns into my main ClassSpecList. Problem is, when I try
answer->push_back(new classSpec (*thisanswer));
It compiles but I get a seg fault
When I try somethign else like:
answer->insert(ClassSpecList.begin(), *thisanswer);
I keep getting primary expression errors and I do not know why. I even tried it with other list made without typedef and I still get those.
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Jul 27, 2013
So I'm trying to fill a vector with pointers to account objects.
std::vector<account*> fill_vector() {
std::vector<account*> temp;
std::ifstream s;
std::string str;
s.open("H://account2.dat");
[Code] ....
The accounts have four different types and I am supposed to skip over ones that have an invalid account type and throw an exception:
account* factory(std::string account_code, std::string first_name,
std::string last_name, char type, double balance) {
try {
if(type == 'A') {
simple_account *a = new simple_account(account_code, first_name, last_name, balance);
[Code] .....
My problem is they program will not skip over my rejected accounts.. still adds them to the vector but I cant figure out why!
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Sep 4, 2012
Code:
void Class1::Func(shared_ptr<type1> parameter)
{
}
or
void Class1::Func(const shared_ptr<type1>& parameter)
{
}
or
Should I ever pass arguments/parameters to other objects using shared_ptr's or raw pointers?
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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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