C/C++ :: Implementation Of A Vector Of Structures
Apr 14, 2014
I created a structure Vector and implement some functions to make the new defined type (vector) dynamically allocated and resized (inspired from the C++ implementation of the dynamic arrays : vector). I need to assign a structure to every vector element but I am not sure that I am doing it right:
here is the structure that I've defined:
typedef struct {
void** mem; // to make this parametrizable I want the void* to point to a Structure (referenced with * a pointer)
unsigned long elems;
unsigned long elemsize; //element size
[Code] ....
I believe I have serious problems with pointers, values and dereferencing a pointer.
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Jul 5, 2013
I have asked a related question before, and it was resolved successfully. In the past, when I wanted to use std::max_element in order to find the maximum element (or even sort by using std::sort) of a vector of structures according to one of the members of the structure, all I had to do was to insert a specially designed comparison function as the third argument of the function std::max::element. But the latter comparison function naturally accepts two arguments internally.
For instance, here is a test program that successfully finds the maximum according to just one member of the structure:
Code:
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
[Code] ....
And the output was this, as expected:
Maximum element S.a of vector<S> vec is at: 9
[I]max element of vec.a between slot 3 and slot 6 is: 6, and its index is: 6 vec[6].a = 6
[I]max element of vec.a between slot 4 and slot 7 is: 7, and its index is: 7 vec[7].a = 7
[I]max element of vec.a between slot 5 and slot 8 is: 8, and its index is: 8 vec[8].a = 8
[I]max element of vec.a between slot 6 and slot 9 is: 9, and its index is: 9 vec[9].a = 9
However, I now need to search and find an element of vector<myStruct> according to just one member of myStruct, instead of finding the maximum or sorting as before. This presents a problem because the function std::find does not accept such a comparison function as its third argument.
This was the description of the std::find function that I found: find - C++ Reference
Code:
template <class InputIterator, class T> InputIterator find (InputIterator first, InputIterator last, const T& val);
I could also find another function called std::find_if, but this only accepts a unary predicate like this: find_if - C++ Reference
Code:
template <class InputIterator, class UnaryPredicate> InputIterator find_if (InputIterator first, InputIterator last, UnaryPredicate pred);
And once again this is either inadequate of I don't see how to use it directly, because for the third argument I would like to insert a function that takes two arguments with a syntax like this:
Code:
int x=7;
std::vector<S>::iterator result;
result = std::find(vec.begin(), vec.end(), []( const (int x, const S & S_1) { return ( x == S_1.a ) ; } ) ;
Is there another std function that I can use to make search and find an element according to just one member of myStruct?
Or perhaps there is a clever way to pass two arguments to the unary predicate.
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Mar 1, 2015
There appears to be some kind of error in by removeMin() function. Inserting items seems to work just fine but attempting to remove any items gives me the error "vector subscript out of range".
Here is my SortedPQ class... Below it you will find the quicksort implementation, in case looking at it is necessary.
template <class Type>
class SortedPQ {
private:
int front;
int rear;
vector<Type> V;
public:
SortedPQ(void) : front(-1), rear(-1), V(0){}
[Code] ....
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Aug 18, 2013
I have to develop minimalistic implementation of RSA algorithm in C for an embedded device.
I'm doing that for two days but I have run into a problem. The N modulus is the limitation for the maximum message value to be encrypted with RSA.
For example theoretically RSA-1024 can encrypt/decrypt messages 1024 bits long but I still cannot understand how to choose p and q values to produce N == pow(2, 1024).
Is it possible to encrypt/decrypt 1024 bits long messages in practice if the N < pow(2, 1024)?
So far I'm getting the following results
Code:
Encrypting with RSA
d=15689981, e=21, n=16484947
In=16484942, Encrypted= 6074492, Out=16484942 (OK)
In=16484943, Encrypted= 5468920, Out=16484943 (OK)
[Code] ....
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Aug 8, 2013
I was trying to implement Big Integer Implementation. I wanted to start with the basic operation of addition. I am having some problems with operator overloading part
/**
BigInteger implementation
*/
#include "conio.h"
#include "iostream"
[Code]....
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Apr 19, 2014
I was looking at this tutorial: [URL] ..... And I was wondering if implementing it in MVC would be pretty much the same way? How would I display feed items in the views page using?
I tried something like:
ReaderModel Reader = new ReaderModel();
Collection<Rss.Item> List;
List = Reader.GetFeed();
ViewData["RssItems"] = List;
// then in index.cshtml
@foreach(Collection<Rss.Item> items in ViewData["RssItems"]) {
<h3>items.Title</h3>
...
}
I don't think this is right as I'm getting those red error lines...
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Aug 5, 2013
Here is the code,
Code:
class A {
private:
void* operator new(size_t size);
};
int main() {
return 0;
}
The code above compiles fine without errors. But operator new might not have implementation body?
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Jul 9, 2013
I've been working on creating a simulator to crash two galaxies together as part of a project to stress test a CUDA super computer. I've got a long way to go and am currently just working on correctly simulating n-body gravity functions. First I will use this to simulate the cores of the galaxies (the black holes) and eventually the stars.
So long story short I'm working on the beginnings of a gravity simulator. At this point I found some basic code that works well but doesn't quite give the effect I'm looking for.
The code below only pulls each object towards each other like a spring faster and faster until they shoot off into infinity. I try to give one of my bodies an initial velocity to get it to orbit another, but it always just shoots straight at the other body. I'm thinking I need to factor in inertia so that the initial velocity doesn't just get calculated away really fast by the other calculations.
I'm really looking for a bit of direction to get a real gravity simulator with orbits and such working right so eventually I can scale it up to a galaxy, throw in 100B stars and let the CUDA run for a month..
Code:
void update_galaxies(GLdouble elapsedTime) {
//Calculate gravity simulations
GLdouble r1, r2, r3;
r1 = r2 = r3 = 0.0;
for(unsigned int i = 0; i < galaxies.size(); i++)
[Code] ....
As you can see, I'm calculating all the bodies in a vector called "galaxies" with each other, and doing a basic gravity calculation to it. The update_position function simply takes the calculated acceleration and uses it to calculate the velocity and position based on the "elapsedTime".
I think I need to use the Varlet or Runge-Kutta integration methods, after doing a bit more research.
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Mar 12, 2013
I'm having problems with implementing depth first search.
Code:
6 10 //6vertices 10edges
0 2 //vertex and its adjacent vertex
1 0
1 2
2 3
2 4
3 1
4 1
4 3
4 5
5 3
Output to terminal: 0 2 3 1 4 5
but it should be: 0 2 4 5 3 1
Here's my code:
#include<stdio.h>
#include<assert.h>
/* maxVertices represents maximum number of vertices that can be present in the graph. */
#define maxVertices 100
void Dfs(int graph[][maxVertices], int *size, int presentVertex,int *visited)
[Code] ....
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May 31, 2014
Code:
#include <stdio.h>#include <unistd.h>
#include <stdlib.h>
#define STACKSIZE 100
struct stackk
{
int top;
int items[STACKSIZE];
};
typedef struct stackk *s;
[Code]...
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Apr 7, 2014
I am trying to implement a stack class which has struct data type as its private member. I am getiing the following error ,
bash-3.2$ g++ stack_str_arr.cpp
stack_str_arr.cpp: In member function ‘void stack::push(int)’:
stack_str_arr.cpp:39: error: ‘top’ was not declared in this scope
stack_str_arr.cpp: At global scope:
stack_str_arr.cpp:43: error: no ‘void stack::display()’ member function declared in class ‘stack’
Code:
#include<iostream>
using namespace std;
#define MAX 5
class stack {
public :
stack();
[Code] ....
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Sep 19, 2013
I'm implementing a 4x4 matrix class and all is going well until the inverse function turned up. I'm trying to implement the inverse function, but I can't seem to get my head around it.
I've tried the internet, but found nothing useful. Also, I've looked into source code of other programs/libraries that implement a matrix class, but the code is unreadable.
How I can implement this damn 4x4 inverse function? I know the process of inversion, but putting that process into code is proving quite a challenge.
In addition, I do have some code, but it's unmanageable and inefficient at the moment. If you want to see it, just ask.
Additional question(s): What applications does the inverse matrix have in 3-D?
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Nov 22, 2014
I'd like te have a heap which contains any item inserted by me. However, when I insert the values, if I delete the min value of this coded heap twice, I get the min value uncorrect.I could not find where the mistake is.
Code:
void BinaryHeap::percolateDown(int hole) {
int child = hole*2;
while (child < size) {
[Code].....
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Sep 12, 2014
I am trying to implement some kind of named class. It would look something like this:
class MyClass {
virtual std::string getName() = 0;
};
And now (what doesn't pass the compilation)
template <std::string NAME> class MyNamedClass {
std::string getName() { return NAME;}
};
And so every time I would like to have a class with a name, I could just do the following:
FinalClass : public MyNamedClass<"FinalClass">{};
The idea is not to have to always reimplement getName(), and just do it concisely in the declaration.
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Aug 26, 2013
I was trying to implement a hash function in c++. This is just for learning purposes and not for a class project or assignment question. I had some questions before I started programming it:
1) Is it meaningful to have a hash function which maps string to string, string to int, int to int, float to int?
2) Can we have a template implementation which does element to element hashing?
I looked at several sources for a clear understanding of concepts and implementation technique but could not find a good source for reading about hashing.
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May 11, 2013
I am currently trying to implement a pathfinding algorithm using c++ and opengl. My code so far is shown below:
#define OPEN 1
#define CLOSED 2
#define UNVISITED 3
#define BLOCKED 4
#define HIGHLIGHT 5
#define ONROUTE 6
#define GOAL 7
#define GSIZE 20 // size of tile grid
#define ISTART 15 // index position of starting tile in grid
[Code] ....
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May 5, 2014
How can we implement an expression parser in C++.
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Apr 19, 2013
So I'm going through and trying to do a recursive implementation of a Heap. I keep getting access violations for some reason on my sifts (_siftUp) - even though I'm trying to insert into sub[0] (currSize = 0 in the constructor). I don't think either of my sifts are implemented correctly, are they?
Here's my Heap:
Code:
#ifndef HEAP_H
#define HEAP_H
//**************************************************************************
template<typename TYPE>
[Code].....
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May 13, 2012
What is the benefit on separating the abstraction and implementation.
The below code
Code:
class FileProcessor {
public:
virtual void processFile();
};
class DocProcessor : public FileProcessor
[Code] ....
Till now it is fine. suppose DocProcessor and ExcelProcessor uses two big algorithm to process these file types then I still can have subclasses like :
class Algorithm1 : public DocProcessor
{
public:
void algorithm(); //which will be called as per the algorithm class instantiated for to process
};
[Code] ....
same for ExcelProcessor class
Here everything looks fine to me. [ I have not used the bridge pattern to separate the abstraction and implementation]. The only thing i can achieve using bridge is that the number of classes will be reduced if new class like jpgProcessor is introduced or new algorithim is introduced.
Then why it is recommended that always separate the abstraction and implementation...
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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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Jun 7, 2012
I have a cpp app that reads in a number of files and writes revised output. The app doesn't seem to be able to open a file with a ' in the file name, such as,
N,N'-dimethylethylenediamine.mol
This is the function that opens the file :
Code:
// opens mol file, reads in rows to string vector and returns vector
vector<string> get_mol_file(string& filePath) {
vector<string> mol_file;
string new_mol_line;
// create an input stream and open the mol file
ifstream read_mol_input;
read_mol_input.open( filePath.c_str() );
[Code] ....
The path to the file is passed as a cpp string and the c version is used to open the file. Do I need to handle this as a special case? It is possible that there could be " as well, parenthesis, etc.
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May 13, 2013
I need to create a class vector as a template and define operations on vectors.
And this is what I made.
#include<iostream>
using namespace std;
template<class T>
[Code].....
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Feb 13, 2013
How a graph can be implemented in the form of a c program?
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Apr 12, 2013
I'm trying to code one of the problems but it really is hard to catch errors for a novice like me at first.
I have to Write a single C function for computing the histogram of a list of nonnegative integers into 4 bins.
The main() function first initializes a positive integer array called List of size N, takes 3 inputs from the user A, B, C (assume 0 < A < B < C), and declares a second integer array Bin[4].
The doBinning function should count the number of elements of List in the interval [0, A) and store it in Bin[0], count of [A, B) in Bin[1], count of elements in [B,C) in Bin[2], and the number of elements >= C in Bin[3]
Code:
#include <stdio.h>
#define N 10
#define M 4
int *doBinning (int source[], int dest[], int a, int b, int c);
int main (){
[Code] ....
Somehow I keep getting error from ptr = doBinning(List[], Bins[]. What am I doing wrong? Code might contain some errors.
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Mar 23, 2013
I am trying to create a code to represent a queue using a linked list but i get the disturbing "Segmentation fault coredumped" after compilation.
Code:
#ifndef QUEUE_H
#define QUEUE_H
#include <stdbool.h>
typedef int Item;
typedef struct queue_type *Queue;
typedef struct node *return_node;
[Code] .....
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Aug 26, 2014
I implemented Anisotropic Diffusion for 2d image in C language in order to develop "Brain Surface Extractor". My code is having some flaw which I am not able to find.Its taking a pgm image as input and not producing the expected output which is the "Edge highlighted image".
Code:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define SIZE 128
typedef struct PGM {
[Code] .....
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