C++ :: Sequence Of Actions - Delete Pointer In Vector
Jul 29, 2013
I'm tying to create a program that evaluates all possible actions for a certain problem.
So what i'm basically trying to do is to create a sequence of actions, evaluate them to check if it's the best sequence, change the sequence, evaluate again and so on until all possible scenarios are exhausted, leaving the best one in the end.
My approach to this at first was to create a tree of all possible options and then evaluate each branch. Since there are a lot of possible cases i ran out of memory while the program was still creating the tree. I changed this to create just a branch, evaluate it and then modify it.
I was still getting memory problems. I declared a class tNode and declared a vector<tNode*> branch. Then i created all the nodes i needed for that branch with branch.push_back( new tNode() ). When i wanted to modify the branch i simply used branch.pop_back() and again a branch.push_back( new tNode() ). I figured i was getting the problem because although i clear the vector, i don't actually clear the reference in memory. Is this correct? If so, how can i actually delete the memory space and not just the pointer in the vector?
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Apr 17, 2013
I have following:
struct Point {int* a; int b;};
vector<vector<Point> > numbers;
vector<int> example;
The numbers vector has a matrix of a sort and each of the members are pointing to one member in the example vector. A member numbers.at(2).at(3).a is pointing at example.at(3). Now, can I remotely delete a member in the example vector using the pointers? Like so:
delete (*(numbers.at(2).at(3).a));
I know there is a more convenient way to delete members, but this is a very specific case I'm working on.
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Feb 25, 2015
An attempt to create a class which is basically a mimic of vector<int> i don't seem to know how to delete pointer x in a destructor to free memory, also on pushback and pushfront methods, i can't free y when i implement delete[] y; y=NULL; i get some NULL out put when cout 'ing the object in main, why is that happening and how do i free memory y.
#include<iostream>
using namespace std;
class vectorOfint{
int* x;
int size;
public:
vectorOfint();
[Code] .....
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Dec 1, 2013
My delete is not working. Why?
Code:
struct MatchName{
MatchName(string& searchName) : s_(searchName) {}
bool operator()(const clsStudent* student) const {
return student->getName() == s_;
[Code] .....
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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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Jul 25, 2013
I have something like this:
class A {
};
class B : public A {
};
class C : public A {
};
B*b1;
B*b2;
C*c1;
C*c2;
vector<A*>vec;
int main() {
vec.push_back(b1);
vec.push_back(b2);
[Code] ....
And it don't works at all. all i get (when playing with variations of this stuff until it compiles correctlly) is a memory leak.
For example, let say i have b1 address = 1234
I will effectively free the memory at 1234, but for a strange reason, the memory leak is elsewhere, for example, at 2345, and the memory value at this address is equal to... 1234, the address of the pointer i wanted to delete.
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Jan 4, 2015
void myfuncion(){
int *a = new int[10];
int b[10];
int *p = b;
delete a
delete p
}
I cant delete b and/or p but how can i check it if i can use delete or not?
i want to check if the pointer is pointing on function temp variable ( those what gets deleted after function ends .
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Sep 2, 2014
int * ptr = new int[5];
p += 2; //p now stores address of 3rd element in array
delete [] p;
what will be deleted??? all 5 elements or just 3rd, 4th and 5th elements of array(in result making a memory leak)
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Apr 15, 2013
let's say I have class LinkedList:
class LinkedList
{
public:
class Node
[Code]....
Do delete newL:
1) (*newL).~LinkedList
2) delete newL
3) delete[] newL
4) none of the above ;)
If the answer is 4, what should I do?
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Dec 14, 2014
I have this class I have been working with,
Code:
// objects to hold results, row id, and name
class result_holder {
public:
// initialize class members
result_holder() : row_id(0), row_value(0.0), row_name("") { }
[Code] ....
There are cases where I need to find an object based on the value of row_id and delete the object from the vector row_results. I could find the proper object by looping through the vector and testing against each member.
Code:
// id I am looking for
unsigned int id_to_delete = 12;
for(i=0; i<row_results.size(); i++) {
if(id_to_delete == row_results[i].row_id) {
delete row_results[i];
}
}
I have used find before to find the position in a vector with a specific value, but I don't know how to use find to locate a specific value for an object member.
Also, is delete what I need to get rid of the object or should I be using erase as in,
Code:
// id I am looking for
unsigned int id_to_delete = 12;
for(i=0; i<row_results.size(); i++) {
if(id_to_delete == row_results[i].row_id) {
row_results.erase(row_results.begin()+i);
}
}
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Apr 23, 2012
Just doing some work where i need to produce a database in C++ for DVD now I have done most of it but I'm stuck on some bits. I have split the database up into different files but I will post the files which are important. How to do a search function. I got told it's called "Bubble search" and then a delete function which i think is called "Vector delete".
My header file
Code:
#ifndef DVD_DB_H
#define DVD_DB_H
#include "dvd.h"
#include <vector>
class dvdDB {
private:
std::vector<DVD> dvds; // A container that contains an arry of DVDs
[Code] .....
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Aug 7, 2014
In jumping into C++ it says something like this: It's not necessary but when you delete a pointer it's a good idea to reset it as a null pointer. That if your code try's to dereference the pointer after being freed, your program will crash. This happens to a lot of experienced programmers.
This could corrupt users data. delete p_int;
p_int = NULL;
1. If you can deference a pointer after the memory is freed, why can't you just delete the pointer?
2. If you can do 1, how do you delete the pointer using code?
3. Every thing I've read says that free memory is handed out in a sequenced order. I don't believe that is true at all. I may be wrong. Why can't you put the data in any number of places if it will fit. Isn't the compiler smart enough to know where bytes (bits)and pieces are stored?
4. If you storing anything in free memory must use a pointer to it?
5. Can a pointer or something similar be used with stack memory?
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Feb 22, 2012
environment : qt creator 4.7
code:
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
using namespace std;
class singleTon {
[Code] ....
this is a singleton pattern first,it doesn't matter, why I could delete this pointer twice?because the gcc compiler?That mean in the surface, "delete pInstance1;" this movement just mark the memory pInstance1 has been deleted but not real?does any one encounter this phenomenon?
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Dec 3, 2013
I have little problem which causing memory leaks.
Parent > Multiple Child(Parent parent) > Child destructor deleting parent => next Child destructor crash
Example code: without using:
class Parent {
public:
Parent() {
for(int i = 0; i < x; ++i) {
for(int j = 0; j < y; ++j)
childs[i][j] = new Child(this);
[Code] ....
If you read code, on Parent destructor i = 0 & j = 1 its going crash.
Parent will be deleted aswell, but it give me assert: _block_type_is_valid(phead- nblockuse)
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Nov 26, 2013
I want the phrase "BUY TICKET" to trigger something, i'm thinking an if statement, and then assign the number after the phrase to another variable. There will also be other commands entered from the input file such as "BUY RAFFLE' "TOTAL REVENUE" on the following lines. Sounds like I need to compare a string(?) to a constant phrase, and if they match have it run the specific code?
Code:
//scan in from file
fscanf(ifp, "%c", &input);
if (input == 'BUY TICKET'){
//Run this
}
How to do it using the tools in C.
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Dec 22, 2012
Goal: To allocate some memory as a char*, read in some binary data, re-interpret it as a float* and then free the memory.
My code looks like:
void someFunction(float* &result) {
char * tmp = new char[1000];
//...Fill the char buffer here...
result = (float*)tmp; //Reinterpret binary data as floats
[Code] ....
Is the cast back to char* necessary on the red line (or could I have validly left it as float*)? Would it be different if I had written char * tmp = (char*)malloc(sizeof(char)*1000); on the blue line (and correspondingly used free (char*)floatData on the red line?
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Oct 16, 2013
I am looking for direction on what topic I should be reading up on. I am new to C++ and Windows MFC.
This is my real world problem, in the context of the application user. (these term do not refer to OPP concepts)
I want to create shapes (containers) in an application that will respond and collect other objects;
Imagine a Windows frame, containing several 2 dimensional squares. I want to be able to drag and drop marbles into the squares,and have the square retain and display the marbles in the square, in the order that they were dropped in.
How do I create the shapes, and how will the square sense when a marble is over it?
How would I create irregular shapes (a combination of lines and curves) that would be responsive to the marbles?
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May 1, 2013
Write a user-friendly C++ program that allows a user to select repeatedly an operation to be performed from a displayed menu of actions. The menu includes the following items:
1. Simple Statistics
2. Vector Addition
3. Dot Product
4. Exit
The menu actions are described by the following points:
Simple Statistics: This action includes finding the average, and standard deviation of a list of data items. The option should allow the user to specify the name of a file from which the data are read into an array. All the results of this option are displayed on the screen.
Vector Addition: This action allows the user to enter the name of a file from which two vectors, V1 and V2, of equal size N are read. Accordingly, the two vectors are added, and displayed along with the resultant vector on the screen. Your program should check that the two added vectors are of the same size. Otherwise, the program should display a message and allow the user to make another choice from the menu.
Dot Product: This action is similar to the Vector Addition in terms of input, output, and checking validity of the vector operands.
Exit: This action terminates the program.
Your program should include at least the following functions:
1. A function, called ReadVector(), which reads a vector of any size from a given file name, and returns the vector and its size to the caller. The function prototype is defined as follows:
void ReadVector(double V[], int &size, ifstream infile);
2. A function, called DisplayMenu(), which displays the menu and returns the user’s choice as an integer value between 1 and 4. The function prototype is defined as follows:
int DisplayMenu (void);
3. A function, called VectorAdd(), which performs the addition of two vectors, A and B, and returns the resultant vector, C. The function prototype is defined as follows:
void VectorAdd(const double A[], const double B[], double C[], int size);
The sum of two vectors, A = (a1, a2, …, an) and B = (b1, b2, …, bn) of size n, is defined as: C = A + B.
Where, C = (c1, c2, …, cn), and ci = ai + bi, for1 i n .
4. A function, called DotProduct(), which performs the dot product of two vectors, A and B, and returns the result. The function prototype is defined as follows:
void DotProduct(const double A[], const double B[], int size, double &result);
The dot-product of two vectors A = (a1, a2, …, an) and B = (b1, b2, …, bn) of size n is defined as
n n
n
i
i i b a ....... b a b a b a B . A
1 1 2 2
1
5. A function, called Simple_Stat(), which finds the maximum, minimum, average, and standard deviation of a list of data items passed to it by a one-dimensional array. The function returns the average and standard deviation values. The function prototype is defined as follows:
void Simple_Stat(const double list[], int size, double &average, double
&std_dev);
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Sep 30, 2014
My problem is that I have two classes that both need members from each other, so I need to use forward declaration + pointers, etc. However, trying to access a vector from a pointer throws an error.
Here's the code:
for(int j = 0; j < level->GetCollisionObjects().size(); j++){
if(fr.intersects(level->GetCollisionObjects()[j])){
rotate = false;
}
}
level is a pointer to class Level. This function is inside class GamePiece. Class Level includes class GamePiece, but GamePiece needs access to the vector CollisionObjects. This function throws a vector size error, and I'm totally lost on what to do.
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Mar 16, 2012
I have a pointer to a vector that contains instances of class Test:
Code:
vector<Test*>* testVec;
If I do this:
Code:
Test* one = new Test();
tectVec->push_back(one);
this crashes. What do I need to do to declare the dynamic memory so this works?
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Jul 30, 2014
Ok here is the code
//assuming that all the directives have been included here
void ptrPointer(vector<string>* const p, int n);
int main() {
vector<string> inventory;
vector.push_back("sword");
vector.push_back("knife");
[Code] .....
Well...my question is how come the last statement or cout statement to be accurate won't work and display? Since we can do something like this below?
string text = "some text";
string *p = &text;
cout << p;
I passed the address of the vector to the function. And then display the address. It is a pretty common operation. But it just won't work. But then we do something simple similar to that of the vector. But it works.
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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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May 9, 2013
I've got a struct called Node that contains, among other things, a pointer to a vector of pgm objects. (pgm is a class i've created)
struct Node {
int label;
vector <pgm> *ptr;
Node* lessNode;
Node* moreNode;
};
in another class, i create a vector and a Node and am having trouble assigning the pointer in the Node to point to my new vector.
vector <pgm> lessData;
Node* left;
left->ptr=&lessData;
This all compiles ok, but the last line in the code above causes a segmentation fault. I should mention Node is declared on its own in Node.h and what pgm is. including pgm.h in node.
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Mar 14, 2014
struct mystruct{
int n;
};
class mscope{
public:
std::vector<mystruct> mv;
[Code] .....
So I have a vector of structs and I want to traverse it, find a struct that matches a constraint and obtain a pointer to that struct. I made a function for this purpose which takes a number and an empty pointer that will store the reference. However, after function returns the pointer becomes null. What could be causing this?
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Mar 30, 2013
"Write a declaration for a function that takes two int parameters and returns an int, and declare a vector whose elements have this function pointer type."
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Mar 6, 2013
Below is a working program. Please note that the vector <int*> pointer is declared as a public member of the class A.
The problem arises when I try to make it a private (instead of public). First, let's look at the File 1 below. It compiles and works fine.
File 1: main.cpp (working fine)
#include <vector>
#include <iostream>
using namespace std;
[Code].....
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