C/C++ :: How To Add Objects To A List Of Pointers
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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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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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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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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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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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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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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Mar 13, 2014
I've a big problem. I'd like to generate of all permutations of objects present on my list and i don't know how to do this. I've found a few examples, but i can't use them in my code...
#include <iostream>
#include <string>
#include <list>
#include <fstream>
#include <cstddef>
#include <cstdlib>
#include <iterator>
using namespace std;
class Item {
private:
[Code]...
Input file with objects:
3
2 0 0 4
5 0 1 5
3 0 2 6
and output should be:
2 0 0 4
5 0 1 5
3 0 2 6
2 0 0 4
3 0 2 6
5 0 1 5
3 0 2 6
2 0 0 4
5 0 1 5
etc... 3! so 6 permutations for this example.
I was 'fighting' with this for few days, and I'm so downcast.
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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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May 18, 2014
Main
#include <iostream>
#include "item.h"
#include "inventory.h"
#include <stdlib.h>
#include <string.h>
#pragma GCC diagnostic ignored "-Wwrite-strings"
[code]....
what I would want to happen is is have my item increment in size/count instead of a new object. How would you handle this algorithmically.
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Jan 16, 2013
Please consider the following code :
#include <iostream>
using namespace std;
class superclass;
class subclass1;
class subclass2;
[Code] ....
As you can see I want to create a dynamically allocated storage of references to a parent class each of which can then point to a child class, how ever I do not know how to extract the child class out again from that array so i may access its variable b.
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Dec 17, 2013
I have a linked list where each node contains a pointer to a string, I'm treating the linked list as a text file and each node/string contains each line in the text file.
I have all of that working, but now I need to create a switchLine function that takes in the two line numbers and I need to switch those lines in the text file. I initially thought of switching the pointers to each the next node in the linked list such that the node order changes, but I then realized how much work that would actually take when you need to consider so many cases. So I instead thought of changing the pointers to strings. If I want to switch the 2nd and 3rd line, then I'd want to have the 2nd node in the list have its char * pointer point to the memory position that the 3rd node's char pointer points to, and vice versa.
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Apr 19, 2013
I have a list of objects that I need to read information from each object to compare to a user input prompt.
#include "Passenger.h"
#include "Reservation.h"
#include "Aircraft.h"
#include <iostream>
#include <fstream>
#include <string>
#include <list>
using namespace std;
//Function Prototypes
void flightRoster(list<Reservation>&);
[Code] ....
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Apr 22, 2014
I am writing a class that dynamically allocates an array that holds a user-defined number of test scores (test scores go from 0 to 10 both included). Once all the test scores are entered and validated (values only between 0 and 10, both included), the array should be passed to a function that sorts them in ascending order. Another function should be called that calculates theaverage of all the scores.The main program should display the sorted list of scores and the average of the scores with appropriate headings.
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Nov 12, 2014
This has been bothering me for a while now, and I finally put together an example:
#include <iostream>
#include <string>
using namespace::std;
[Code]....
In the code above, the two classes hold pointers to each other, and that's fine but it doesn't seem right since C++ prefers to pass by reference. Yes, it can still do that (see testbox and testball) but even that seems odd to me because still you need to use pointer notation for the enclosed object. Am I the only one who feels this way, and should I just get over it? Or am I missing something that would allow an object to hold a reference?
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Feb 28, 2014
I'm trying to create an array of pointers to pointers which will point to array of pointers (to strings) I tried
Code:
int i;
char *string[]={
"my name is dave",
"we like to dance together",
"sunny day",
"hello",
[code]...
the app keeps crashing , I don't know how to make the array-elements to point to another array-elements..
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May 21, 2013
I am a little confused while comparing char pointers to integer pointers. Here is the problem:
Consider the following statement;
char *ptr = "Hello";
char cArr[] = "Hello";
When I do cout << ptr; it prints Hello, same is the case with the statement
cout << cArr;
As ptr and cArr are pointers, they should print addresses rather than contents, but if I have an interger array i.e.
int iArr[] = {1, 2, 3};
If I cout << iArr; it displays the expected result(i.e. prints address) but pointers to character array while outputting doesn't show the address but shows the contents, Why??
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Apr 15, 2013
I'm trying to write a function that takes a 32bit address and a data to store at this address.
I'm wanting to take the 32 bit memory address eg 0x12345678 and split it
into 4 x 2 bytes
12, 34, 56, 78
then each of the 4 entries is at most a 256 entry array.eg
FF, FF, FF, FF
So in this example, 0x12 points to 0x34 in the second array, which points to 0x56 in the third array, which finally points to 0x78 in the last array. This last array holds the actual data.
After successfully doing 0x12345678, say I might get a read for 0x1234AABB. So, the first and second pointers already exist, but I then have to create and write to dynamically created arrays.
The arrays need to have all entries set to NULL so that i know whether to follow the pointers to overwrite a previously entered value or create new arrays and pointers.
It all looks good and simple in the pseudo code I've written up but I'm having trouble coding it. I'm currently trying to deal with the first entry case, ie all array elements are NULL, but I'm getting confused with the pointers and creation of new arrays.
void cpu::store(unsigned int mem_add,unsigned int mem_val) {
int first = (mem_address&4278190080)>>24;
int second = (mem_address&16711680)>>16;
int third = (mem_address&65280)>>8;
int fourth= (mem_address&255);
[Code] .....
A1 has been declared as
int* A1[256] ;
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Apr 23, 2013
From HP / Microsoft (Visual Studio C++) <list>:
Code:
struct _Node
{ // list node
_Genptr _Next; // successor node, or first element if head
_Genptr _Prev; // predecessor node, or last element if head
_Ty _Myval; // the stored value, unused if head
};
The stored value is wasted space for the list head. Is there any advantage to implementing list using the same structure for a list head and node?
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Dec 31, 2014
Code:
// Write a function called insertEntry() to insert a new entry into a linked list.
Have the procedure take as arguments a pointer to the list entry to be inserted (of type struct entry as defined in this chapter), and a pointer to an element in the list after which the new entry is to be inserted.
// The function dveloped in exercise 2 only inserts an element after an existing element in the list, thereby prenting you from inserting a new entry at the front of the list.
(Hint: Think about setting up a special structure to point to the beginning of the list.)
#include <stdio.h
struct entry1 {
int value;
struct entry1 *next;
};
[code]...
This is a working version of the exercise, but I don't think I'm doing what's asked. I was able to add an element to the beginning of the list using an if statement, not creating a special structure that points to the beginning of the list. How would I go about creating a special structure that points to the beginning of the list to add a new element at the beginning of the list?
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Jan 20, 2015
I'm trying to display a list of MSMQ messages in a list box based on a drop-down list holding the environment.So i've setup the binding and i know that the list loads but nothing shows up in the list? I should be setting like a display member or something but i'm not entirely sure
const String msmqAccelaDev = "FormatName:DIRECT=OS:tcc-intsrvTCCIntegration.MSMQ.Service.Dev/TCCMessagingService.svc";
const String msmqAccelaProd = "FormatName:DIRECT=OS:tcc-intsrvTCCMSMQFail";
const String msmqAccelaTest = "FormatName:DIRECT=OS:tcc-intsrvTCCIntegration.MSMQ.Service.Test/TCCMessagingService.svc";
String currentQueue = "";
private void environmentChange()
[Code]...
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May 30, 2013
I'm working on a linked list and was wondering how this looks to everybody else for a deleteList function.
void deleteList(Node* head)
{
Node* iterator = head;
while (iterator != 0)
[code].....
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Apr 2, 2013
i am relatively new to c++, and am trying to make it so particles will gravitationally attract to the mouse pointer. i have gotten all the bugs that the compiler found, but there must be another because the program crashes the second i open it. my code could be way off, so just tell me if it is and ill do more research and learning before trying something like this again. here is the code:
#include <SDL/SDL.h>
#include <iostream>
#include <vector>
#include <math.h>
#include <stdio.h>
using namespace std;
float mouseX;
float mouseY;
[Code] .....
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