so lets assume i have a nested vector in a set or vice versa o in a more general form a container in a container example...
Code:
std::set<vector<int> > my_tuple;
How do i access individual elements of lets say the first vector in the set! Or the last element in the 3rd vector?
i had a structure as follows:
struct a{
int x;
struct b{
int y;
b *next;
}b;
};
when i try to access as follows:
struct a *a;
a->b=a->b->next;
i got the following error: base operand of ‘->’ has non-pointer type
I have two classes, a Package class and a Person class. The Package class has two Person objects has member variables, a Sender and a Receiver. While overloading the << operator for the Package class so that it will make an output label from everything in the Package class. Here is my code...
class Package{
public:
Person Sender;
Person Reciever;
int weight;
double cost;
friend ostream &operator<<(ostream &out, Package &pack);
[Code] .....
So my problem is on that last output line, I am unable to call Sender.getName()... etc. Is there a proper syntax so that I can access the members of the Person class while overloading the << operator for the Package class?
I'm confused about accessing elements from arrays. Supposed I have an array of pointers to char:
char *names = { "John", "Rose", "Steven" };
To access one of the strings, should I use names[ 0 ][ i ], where i is an index in the set ( 0, 1, 2 ), or should I use names[ i ]? I would think it would be the first option, because this array has 1 dimension that contains others arrays, right?
I want to access the elements of my array dynamically. So far I've only figured out how to do this manually. if I tried it like this my code would work but there should be a better way right?
View 10 Replies View RelatedI am trying to retrieve the elements in an array to print them. I am pretty sure I have everything right, but it is not working. There are 5 values in the array {3, 4, 10, 5, 6}, but the first two elements (supposed to be 3,4) are coming out a 0,-2654238590. The last three elements are coming out correct.
void addDynArr(DynArr *v, TYPE val) {
/* FIXME: You will write this function */
assert(v != 0);
//resize if necessary
if(v->size >= v->capacity)
[Code] ....
I've been working for some number of days on this code to take information about movies from both a file and the user, store the infos in an array of structs, and at the end, write all the info out to a file. I'm having some problems with an error message reading:
"prog.c:102:11: error: subscripted value is neither array nor pointer nor vector"
this error occurs in many lines (which I will label specifically below -- they are everywhere where I am trying to access/modify an individual element of a struct element of the array).
A few examples of where I am having the problems are lines:
39, 52-55, 70, 72, and 86 (and more of the same exact variety).
I am obviously rather systematically doing something wrong, but I am quite certain all of these are the exact same mistakes.
I pull up also 2 or 3 other errors, but I don't think they are related and should be able to fix them quickly once I work out this conundrum.
#include <string.h>
#include<stdlib.h>
#include <stdio.h>
int moviecount =0;
typedef struct{
int year;
[Code] .....
Code:
int arr[10];
int* p = arr;
int (*p2)[10] = &arr;
So, pointer p is a pointer to an array, I can use it to access elements of arr as in *(p+5).
Pointer p2 is a pointer to an array of ten integers. What is it for, how can I use it to access elements of arr?
I have a nested record structure in C++ that contains a FileHeader record, a RecordHeader record and a DataRecord record. The last item is an array of unknown size (at compile time). I have to open a file and read the array size and then create the array.
I have worked on this for some time and can't figure out how to make it work. I know the sample data I am using has 85 records. I insert 85 into the array size and it works fine. But how do I create a dynamic array or define a vector within a nested structure?
1. What is the best (easiest) method to accomplish this (array or vector)?
2. How would it be implemented/how do you add data to it?
PreviousLogRecord.FaultRecord.push_back(field1); // does not work
PreviousLogRecord.FaultRecord[recordNumber].field1 = somedata; // works with 85 in array size.
struct LogFileHeaderRecordType {
QString field1;
int field2;
[Code] .....
I have the following map: myMap<string,vector<int>>. I now want to look through my map to see if a key exists and if it does, retrieve one of the int values from within that vector. What would be the best way to do this? Right now I have the following:
What would be the best way to look for a key and get one of the int values from its vector value? Right now I'm doing something like this:
[code]
map<string,vector<unsigned int>>::iterator it;
it = wordMap.find(someWord);
if(it == wordMap.end){
cout << "No matching entry";
} else{
// this is where I'd want to access the value (the vector) of the map
}
Is there a better way to do this?
Is it possible to pass the vector index '4' to the Height() function without passing it as a parameter of the function.
Basically, I'm trying to eliminate using 4 twice... what I'd LIKE the statement below to look like is this:
gx.Cell[4].Height();
The only way I can figure out how to get it to work is like this...
class grid{
public:
class CELL{
public:
int Height(int index); //returns the height of this cell
[Code] .....
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.
How I can use class functions in a vector. I have 2 classes:
Gamemode class
bullets class
Inside the Gamemode class I declared: vector<bullets> Bullet and bullets * b.
If the user presses the shoot button a new bullets class will be added to the Bullet vector:
b = new bullets;
Bullet.push_back(b)
Bow I'd like to check all objects in the Bullet vector for the collision() function inside the bullets class.
I already set up a for loop which counts from 0 to the end of the vector:
for( int i=0;i<Bullet.size;i++)
{
}
My idea was to do something like:
if(Bullet[i].collision()) then erase Bullet[i]
But that doesn't work...
So I have this problem with not being able to iterate over a vector in a nested for-loop. Here's the nested for-loop:
bool innerHit = false;
for (std::vector<Sprite*>::iterator outerIter = sprites.begin(); outerIter != sprites.end() && (!sprites.empty()); outerIter++) {
Sprite* spriteOne = *outerIter;
for (std::vector<Sprite*>::reverse_iterator innerIter = sprites.rbegin(); innerIter != sprites.rend() && (!sprites.empty()); innerIter++) {
Sprite* spriteTwo = *innerIter;
[Code] .....
What happens is, after having called the collisionDestroy-function and the program tries to execute the nest loop in the outer for-loop, it all crashes with the text "Expression: vector iterator not decrementable", which I understand is because the iterator will have already become useless. The question is: know this, how do I fix it? I can't seem to get a hang of it.
Here's the collisionDestroy-function (the collisionReaction does nothing but sets a few local variables):
void Enemy::collisionDestroy(std::vector<Sprite*>& sprites) {
for (std::vector<Sprite*>::iterator iter = sprites.begin(); iter != sprites.end(); iter++) {
Enemy* tmp = dynamic_cast<Enemy*>(*iter);
if (this == tmp && collisionType == 3 || collisionType == 1) {
sprites.erase(iter);
break;
}
}
}
I initialized a nested vector with the following code as:
Code:
vector<vector<Point> > vectorB(4, vector<Point> (int(vectorA.size()), 0));
And came across the following error during link stage:
"/usr/include/c++/4.6/bits/stl_vector.h:1080:4: error: no matching function for call to ‘std::vector<cv::Point_<int> >::_M_fill_initialize(std::vector<cv::Point_<int> >::size_type, int&)’ "
I have a vector that I would like to access and work with from multiple threads. I have created an example below to illustrate the functionality that I would like to accomplish.
The goals are to be (1) high speed, (2) thread safe, and (3) *if possible* continue to use vectors as my larger project uses vectors all over the place and as such I would like to maintain that.
However, if I need to switch from vectors to something else then I am open to that as well.
The following example below compiles but crashes rather quickly because it is not thread safe.
How I can fix the example below which I can then apply to my larger project?
#include <string>
#include <vector>
#include <ctime>
#include <thread>
#include <iostream>
#include <random>
#include <atomic>
#include <algorithm>
enum EmployeeType {
[Code] ....
I have a vector (structures) in a struct (instances). I make a declaration of this struct called instance. The vector is a 3-layer vector of pointers, like so:
vector < vector < vector<scene::IAnimatedMeshSceneNode*> > > structures; (The type is from Irrlicht 3D). I have 3 nested "for" loops which looks similar to the following:
for (int a = 0; a < instance.structures.size(); a++) { /*note:vector size previously set*/
for (int b = 0; b < instance.structures[a].size(); b++){
for (int c = 0; c < instance.structures[a][b].size(); c++) {
if (1) { //checking value of variable not included in snippet
(instance.structures)[a][b][c] = smgr->addAnimatedMeshSceneNode(fl);
(instance.structures)[a][b][c]->setPosition(renderPos);
}
}
}
}
The problem is in these two lines, I think:
(instance.structures)[a][b][c] = smgr->addAnimatedMeshSceneNode(fl);
(instance.structures)[a][b][c]->setPosition(renderPos);
These are currently referencing the pointers, it seems. The program compiles but crashes at this point. I need them to reference the values of the pointers. Problem is, I don't know where to put the dereference operator (*). Where should it go?
i have this vector:
#ifndef new_thing_Inventory_h
#define new_thing_Inventory_h
#include <vector>
#include <string>
using namespace std;
class Inventory {
[code]....
so i know i need to use .push_back or .pop_back, but the program im using dosn't even recognize that inventory is a created vector.
I'm writing a program with a class containing a private std::vector<bool>. I chose bool because the vector represents a 2D array (think grid) and I only need 2 states per cell. I kept it one-dimensional as this hardly complicates things.
My problem is that I don't know how to initialize the vector, i.e. fill it with 0's.
The grid's resolution is not known at compile time, so I imagine I have to set the size (and content) of the vector in the class constructor.
Here's what I have tried among several things:
Code: World::World(const u_short worldsize)
{
grid.reserve(worldsize * worldsize); // grid is the private vector; square dimensions.
std::fill(grid.begin(), grid.end(), 0);
std::cout << grid.size();
} The output is 0. Only std::vector::push_back seems to have an effect on size(), but judging by its description, it doesn't look like the right candidate to populate a vector with zeros. Correct me if I'm wrong.
Frankly I expected line 3 to set the vector's size.
how to swap the first and 'mid' elements of a vector?
View 2 Replies View RelatedI have an integer vector of size "n".
e.g.
std::vector<int> vec;
vec.pushback(0);
vec.pushback(1);
vec.pushback(2);
vec.pushback(3);
Now I want to generate all possible combinations of size = {0, 1, 2, ... , n}.
{0, 1, 3} is not equal to {3, 1, 0} or {1, 0, 3} or {3, 0, 1}
I had a question about memory allocation/how iterators work for a std::vector<foo> of a user defined class 'foo'. Say foo contains variables of variable size, so that each member of the std::vector<foo> does not require the same amount of memory space.
Does c++ allocate the same amount of memory for each element, equal to the amount of memory required for the largest element? Or does it use some sort of array of pointers pointing to the location of each element in the vector to make the iterator work? Or does it use some other method? I am wondering because I wrote a code which reads data from a binary files and stores most of it in std::vectors.
The code seems to be using significantly more memory than the sum of the size of all the binary files, and I am using vectors made up of the datatype within the binary files (float). So I was wondering if internally the code was allocating space for each vector element which is the size of the largest element as a way to handle indexing/iterators. I ran my code through a memory leak checker and it found no errors.
I am currently trying to implement a 2d vector to store x and y of type int.
I have successfully passed it to the function, however i am unable to store the values in it. It always returns with a segmentation fault and my program terminates from there. May i know how do i store them properly and call them out?
Below is my code snippet
int reconstructSecret(int x, int y, vector< vector<int> > &inVec ,int constructSecret) {
int getX,getY,formula,accum,count,getSecret,startPosition,nextPosition,numerator,denominator;
getX=x;
getY=y;
int result;
[Code] .....
The main method
vector< vector<int> > inVec;
for(int i=0;i<constructSecret;i++) {
cout<<"please key in the "<<i<< "share of x value:";
cin>>x;
[Code] ...
I am working on a project for class where I use a parent Shape class with circle, rectangle, ect. Classes inheriting from that. Along side these I use a class called Scene. In main I need to create a scene and add some shapes to a vector in scene.
vector<Shape*> shapes
I need to use functions addShape(Shape* shape) and a delete shape method. I have the addShape finished. The problem I am having is with the delete method. Is there a way that I can use something like deleteShape(Shape* shape)? Is it possible for me to delete a specific shape from the vector by passing in that shape, or can it only be done using index? I have looked at the documentation for std::vector as well as std::vector::erase. I am wondering this because if I use index values and do something like
void Scene::deleteShape(unsigned int x) { shapes.erase(shapes.begin() + x ); }
It will lead to some errors later on due the the changing size and indexes of the vector and elements.
here is a piece of my code:
while(T--)
{
std::vector<std::pair<int, int> > *dragon;
std::vector<std::pair<int, int> > *villager;
[Code]....
I now wish to print the elements of the vector. How do I do it?
"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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