C/C++ :: Manipulating Data Through Own Iterator
Apr 10, 2014
We were given a task to use lists and iterators. We were supposed to make them from scratch. I'm done with that. The problems that I'm having are as following:
1. I'm not able to access the list made of Course datatype which is present in each Student instance. Does this mean I need to make an iterator for that course list inside the student class?
2. Similarly since I don't have direct access to The course list so I added the course into the Student list through the student objects not through the iterator. How can I do it through the iterator?
3. Printing of a particular student and his courses is not happening as my iterator made for student only prints out the students, not the courses present in their courselist. How to do that?
Here's the code
#include <iostream>
#include <string>
using namespace std;
const int ILLEGAL_SIZE = 1;
const int OUT_OF_MEMORY = 2;
const int NO_SPACE = 3;
const int ILLEGAL_INDEX = 4;
[Code] .....
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Jan 31, 2015
So, it seems I have a bug in my code:
Code:
char *mem = malloc(9), *bottom = malloc(3), *in = "abc";
int position = 2, i;
mem = "onetwo";
printf("OLD mem = %s
", mem);
[Code]....
What I'm trying to do is insert "abc" in the 3rd position of "onetwo". Results would be "oneabctwo", but all I get is crashing.
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Sep 28, 2014
How can I manipulate a data in a file for example the saved file is like this:
code name Price Quantity
001 hammer 100 4
002 screwdriver 100 4
what i like to do is:
1. the user will be ask to enter its code
2. will output the searched code and then
3. the user will be ask to enter how many pcs he/she will buy.the formula should be
pcs=pcs-users_input if the user selected the code 001 and enters only 1pc it should be updated to only 3 pcs left in the file.
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Jul 7, 2012
File Data format
A,A
A,B
C,E
C,F
And so on ... it could be up to any alphabet. The number of As and Bs and Cs and Ds in first column depends on the number of unique alphabets used in the first column. For example the unique alphabets used in this case are 2 (A,C) hence each alphabet appears in the first column of consecutive 2 rows.
Which means
Code:
A:A,B,C,D
B:B,C,D,E
C:C,D,E,F
D:D, ,F,G (E is missing)
Actual Data
A,1
A,2
A,3
A,4
C,18
C,33
Final Solution: Add each integer value to its previous value and store the resulting value.
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Dec 17, 2013
I have the following code and I am trying to do simple math calculations to the data. I need to take the car price (y) minus down payment (z) and then divide that quantity by 12 times "yearsx" That answer is then assigned to x. The problem is that x will not print the correctly!I also noticed that if I increase the "count" to amnything higher than the number on lines in the file, I get the correct value for x but only on the last set of the struct..my file reads as follows:
last_name first_name car_price down_payment years
johnson bill 10,000 2,000 3
When I printf the struct to the screen, i need to do the following:
x = (10,000 - 2,000)/(12*years);
but this is the math part that wont work. I have checked and doubled checked number types and I cant get it right.
Code:
#include<stdio.h>
#include<stdlib.h>
#define FILENAME "file.txt"
#define SIZE 100
}
[code]....
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Feb 6, 2015
I found this elegant looking code on the net that claims to be able to manipulate an images colors using ColorMatrix.
When I run it, it does nothing! I used the code exactly as is with no editing, except to feed it my own image to do its work.
private void ApplySaturation(float saturation) {
float rWeight = 0.3086f;
float gWeight = 0.6094f;
float bWeight = 0.0820f;
float a = (1.0f - saturation) * rWeight + saturation;
[code].....
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Jul 11, 2012
I am writing a little OS agnostic library for my team for manipulating files.
One such function is used to move/rename files (only files, not dirs). I got into a little argument with a colleague about naming: "rename" or "move"?
"move" makes more sense, but the c api calls it rename.
Is there any historic (or actual) difference between a "rename" and a "move" we could base ourselves on? Or is this purely an Apples vs Oranges?
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Sep 23, 2014
Implementing and manipulating a Polynomial ADT using a linked list.
So far I have:
poly_ADT.h
Code: typedef struct nodeT{
int coef;
int powr;
struct nodeT *next;
} node;
[Code]...
I need to create a function that creates the polynomial using input first.
poly *poly_create (num,...) ;return a new polynomial with num terms terms are listed in order of lowest ordered-term to highest. i.e., to initialize poly 15x^6 + -9x^4 + 3x^2 call poly_create(3, 3,2, -9,4, 15,6 );
Once I do that I need to implement various functions that can manipulate the polynomial itself but I'm having trouble just with creating the polynomial itself, how to do that using a linked list and nodes?
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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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Mar 1, 2014
Why do most C examples pass a double pointer when manipulating linkedlists? Why can not we just pass a single pointer to the struct?I think using an external reference accessor for a linked list would be a more appropriate solution, yes or no?
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Jun 17, 2013
I'm making my first steps in STL, and I have a few question:
Is there a way to get an iterator to the i'th element in the collection (set or list), instead of just to the end or the begin?
And another question: Let's say I have an iterator, pointing to some element in my collection, and I use erase() (which takes as parameter an iterator that points to the soon-to-be erased element), what happens to that iterator? will it now point to NULL?
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Aug 20, 2014
I have this class with template:
template<template<class, class> class ContainerType>
class Movie {
public:
typedef ContainerType<Actor*, std::allocator<Actor*> > Container;
and i have a member func to find actor in movie according to actor id:
const Actor* findActor(int id) const {
typename Container::iterator it;
Actor* p(NULL);
it=actors.begin();
std::for_each(it,actors.end(),(*it)->getId()==id?p=*it:0);
if (p==*actors.end()) return NULL;
return p;
}
I receive error that no match for operator= in it.
How to declare correct iterator ?the type of actors is Container..
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Apr 8, 2014
Why this code works
Elenco e1;
e1.add(Persona("a","b"));
e1.add(Persona("c","d"));
e1.add(Persona("e","f"));
e1.add(Persona("e","f"));
e1.remove(2); //list of 4 elements
but this not work?
Elenco e1;
e1.add(Persona("a","b"));
e1.add(Persona("c","d"));
e1.add(Persona("e","f"));
e1.remove(2); //list of 3 elements
This is remove method:
Persona Elenco:: remove(int pos){
list<Persona> ::iterator iter=l.begin();
for(int i=0 ;i<pos;i++){
iter++;
}
return *(l.erase(iter)); //erase ritorna un iterator
}
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Nov 18, 2013
Here's a few parts of a program I'm working at. It does compile, and it does work as expected. Anyway Eclipse Kepler marks one line as a bug with the remark Field 'befehl' could not be resolved. The bug sign didn't show up when both classes were in one file.
ScriptInterpreter maintains and processes a vector of Objects, initialised with example data. An iterator of the vector keeps track of the current position while various methods process the data. I've copied the relevant lines only.
I can live with a few wrongly bug-marked lines in Eclipse. What I don't want is any hidden errors that express at some time later.
Is there anything wrong with the code? Anything that's not recommended and compiles anyway? Is anything c++11-specific about the questionable line?
AtomicCommand.h
class AtomicCommand {
public:
int befehl;
[Code] .....
Note that line 9 has a bug sign, too. Eclipse doesn't recognise all my c++11 code.
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Feb 22, 2013
I am running some simulation, in which i need to control the iterator of a multimap, like
multimap<double, int> mapp;
......
int n=6;
for(int i=0; i<5; i++) {
for(auto it = mapp.begin()+i*n; it!=mapp.begin()+(i+1)*n; it++) {
......
However this way of controlling is not possible for multimap. Why and how the make it work? Do I need to overload the operator +?
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May 24, 2013
I can't seem to make the STL iterator class work how I need it to.I am implementing a multi list graph and I need to iterate through my STL list of Vertex pointer objects. I keep getting the error:
Error 1 error C2679: binary '=' : no operator found which takes a right-hand operand of type 'std::_List_iterator<_Mylist>' (or there is no acceptable conversion) and the same for != for my terminating condition.
template <typename V, typename E>
void Graph<V, E>::InsertEdge(V from, V to, E edge) {
list<Vertex<V>*>::iterator iter;
for(iter = m_Vertices.begin(); iter != m_Vertices.end(); ++iter)
[code].....
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Jan 21, 2013
I just figured out that some std functions (for example: copy) need the resource and target objects have iterators to work. Otherwise, the compiler rejects. In case of two arrays, declared as:
double myA[100] = {};
array<double, 100> myB = {};
myA[0] is like a pointer, myB.begin() an iterator, if I do not make any mistake. So, what is exactly the difference between the pointer and the iterator here? They all give the access to elements.
If I need the target of copy to be an array like myA which cannot give an iterator, is there a way to make the command "copy" work for it?
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Jan 25, 2013
I want to get the iterator position after to use find if:
std::list<Texture*>::iterator result = find_if(
texturelist.begin(),
texturelist.end(),
std::bind2nd<CompareTEX>(CompareTEX(),n_tex));
if (result != texturelist.end()) {
return // position result
}
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May 25, 2013
I am receiving the error: Vector Iterator not incrementable. However, when erasing I'm already re-setting 'it' and pre-incrementing at the end of the while-clause.what's wrong?
vector<st>::iterator it = map[0][0].begin();
while(it != map[0][0].end()) {
if((*it).val == 5) {
[Code] .....
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Jan 10, 2013
I'm trying out the code below; it runs and produces the output I'd expect, but could it lead to undefined behavior?
To test with, I show the key and wait for user input; if the input doesn't match the value, the iterator is stored in the vector.
map<string, string> test;
map<string, string>::iterator it;
vector<map<string, string>::iterator> bad_input;
string input;
test["key 1"] = "value 1";
[Code] ....
I am also interested in knowing if I can use an iterator to walk through the vector? I tried
vector<map<string, string>::iterator>::iterator v_it;
for(v_it = bad_input.begin(); v_it != bad_input.end(); ++v_it)
cout << v_it-> ??
However, I couldn't figure out how to access "first" and "second" using this method. Is it possible to do so?
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Jan 5, 2015
I have created a multimap for my road points. The key refers to the road number and the values are vec3 points that make up the road.
I am trying to iterate through the values of each key point and create a road segment at each point on the road (except the last), adjust the values to be on the road points and then store them in a std::vector.
The RoadSegment constructor creates 6 vec3 points and pushes them onto a std::vector.
I have a segmentation fault in the line marked in bold
[for(mapIt = it.first; mapIt != it.second; ++mapIt)]
When i take out the lines creating the new objects and pushing them onto the std::vector it works fine.
std::vector<glm::vec3>::iterator SegIt;
for(int i = 0; i < m_genRoads->getKeyValueData().size(); i++)
{
int numberDesired = m_genRoads->getMultimapData().count(i) - 1;
[Code]...
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Mar 6, 2013
I have a list and a vector, for example like
list<int> mylist = {1, 1, 1, 0, 0, 1, 0, 0}
vector<int> myvec;
I want to create an efficient algorithm to erase all element of value "1", and give these elements to a vector. My code (not efficient) is as follows
for(auto it = mylist.begin(); it != mylist.end(); it++) {
if(*it == 1) {
myvec.push_back(*it);
it = mylist.erase(it);
if(it != mylist.begin())
it--;
}
}
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Sep 4, 2013
I defined the following function to find out the iterator of a certain value in the vector. I defined it as such so if the value exist in the vector then return a iterator of it, if not then return a pointer pointing to nonsense.:
vector<tIndex_t>::iterator unlabelTit(const tIndex_t index) {
for(vector<tIndex_t>::iterator it=unlabelT.begin(); it<unlabelT.end(); it++) {
if(index==*it) return it;
} return NULL;
}
But looks this one is not accepted by compiler, saying I cannot do this kind of comparison like:
unlabelTit(i)!=NULL;
so I just delete the return NULL; and then the compiler giving me warning about no return statement before }.
a pointer pointing to nonsense? how to do that?
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Nov 18, 2013
I'm working on a program where I have a vector full of <myClassType> structs.
I'm trying to insert items into a vector, searching first through the vector to make sure the value isn't already in the vector before inserting it. The "find" function isn't working properly.
I keep getting C2678 "binary '==': no operator found which takes a left-hand operand of type "myClassType" or there is no conversion errors in Visual Studio 2010.
I know it's something having to do with the find function and my iterators, but I can't, for the life of me, figure out what it is.
I've tried switching to const_iterators, but I get the same error message.
void foo::insert(const myClassType& en) {
vector<myClassType>::iterator it;
vector<myClassType>::iterator it1;
it = find(Table.begin(), Table.end(), en.memberOne);
[Code] .....
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Jun 24, 2014
I'm trying to make a function to show the content of maps as follows:
template<typename A, typename B>
void show_map(const std::map<A,B> &src) {
for( std::map<A,B>::iterator it=src.begin(); it!=src.end(); ++it ) {
cout << it->first << " ____ " << it->second << endl;
}
};
However, I got this error in the 'for' line: "error: expected ‘;’ before ‘it’" (and then errors that it is not declared, etc). I'm sure that there is no missing ; in other functions. If you try to write a random line before that you get no error there for example, always in the for.
It is there something that you need to do with iterators when you declare generic datatypes?
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Oct 15, 2014
I got the core dump file so I know exactly which line it crashes. Below are some of the information:
OS: Red Hat Enterprise 5.8
Example snippets of when the crash happen:
Code:
typedef map<int, MyClassObj> MyMapT;
.
.
void someFunction( MyMapT& inMap )
{
for ( MyMapT::iterator iter=inMap.begin(); iter!=inMap.end(); ++iter )
{
.
.
}
}
Using GDB, I am able to find out that it crashes at the "++iter" as the .h file indicate it was a "++" operation for the iterator. Tracing up the stack frame it indicate it crash during the copy constructor of some "__rb_tree_node". I did some Googling and it seems that is some Red-Black tree implementation for the map. Honestly I do not quite understand the Red-Black tree and I believe STL map is a very very well tested container, so the problem must lie in my code so that I can look out for it.
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