I found this post online (dates back to 2013) when I had trouble getting direct access to a specific cell in a vtkPolyData. I am using the latest version: VTK 8.1.1 and it seems like the newer version of VTK still has this issue.
polys->InitTraversal();
for(int i = 0; i < polys->GetNumberOfCells(); i++)
{
polys->GetNextCell(idList); // This sequential method gets the point IDs correctly
int a = idList->GetId(0);
int b = idList->GetId(1);
int c = idList->GetId(2);
}
However, the direct access method seems to have issues
polys->InitTraversal();
for(int i = 0; i < polys->GetNumberOfCells(); i++)
{
polys->GetCell(i, idList); // This method returns wrong ids
int a = idList->GetId(0);
int b = idList->GetId(1);
int c = idList->GetId(2);
}
How can I get the point IDs in a specific cell without looping through all the cell? Isn't polys->GetCell(i, idList) meant to give you direct access to a specific cell?
For direct access, we can use vtkPolyData::GetCellPoints() method. For example we can do
vtkNew<vtkIdList> idL; // or auto idL = vtkSmartPointer<vtkIdList>::New();
poly->GetCellPoints( 13, idL ); // Assuming you want the points for 13th cell
for(auto i = 0; i < idL->GetNumberOfIds(); ++i)
std::cout<< idL->GetId(i) << std::endl;
For looping over all cells I prefer a while loop:
vtkNew<vtkIdList> idL;
poly->GetPolys()->InitTraversal();
while(poly->GetPolys()->GetNextCell(idL)){
for(auto i = 0; i < idL->GetNumberOfIds(); ++i)
std::cout<< idL->GetId(i) << std::endl;
}
Related
I'm trying to write my first real program with dynamic arrays, but I've come across a problem I cannot understand. Basically, I am trying to take a dynamic array, copy it into a temporary one, add one more address to the original array, then copy everything back to the original array. Now the original array has one more address than before. This worked perfectly when trying with ints, but strings crash my program. Here's an example of the code I'm struggling with:
void main()
{
int x = 3;
std::string *q;
q = new std::string[x];
q[0] = "1";
q[1] = "2";
q[2] = "3";
x++;
std::string *temp = q;
q = new std::string[x];
q = temp;
q[x-1] = "4";
for (int i = 0; i < 5; i++)
std::cout << q[i] << std::endl;
}
If I were to make q and temp into pointers to int instead of string then the program runs just fine. Any help would be greatly appreciated, I've been stuck on this for an hour or two.
q = temp performs only a shallow copy. You lose the original q and all of the strings it pointed to.
Since you reallocated q to have 4 elements, but then immediately reassigned temp (which was allocated with only 3 elements), accessing (and assigning) the element at x now is outside the bounds of the array.
If you have to do it this way for some reason, it should look like this:
auto temp = q;
q = new std::string[x];
for(int x = 0; x < 3; ++x)
q[x] = temp[x];
delete [] temp;
q[x] = 4;
However, this is obviously more complex and very much more prone to error than the idiomatic way of doing this in C++. Better to use std::vector<std::string> instead.
In python i can write
s = "dad" * 3
Result will be: s = "daddaddad"
I want to append "tabs" to my string. Something like:
QString tabs = "\t" * count;
What would be a simple, idiomatic way to do it?
You can do it quite simply with a loop:
QString mystring("somestring");
QString output;
for (int i = 0; i < 3; ++i)
output.append(mystring);
//'output' will contain the result string
Please note that the code I provide is in C++, not Python, but the concept still applies (and should be easily ported).
EDIT:
If you need to concatenate single characters, you could do it more easily like this:
int size = 5;
QString output(size, QChar('\t'));
//'output' contains 5 tab characters
Or, if you need to assign to another string (output is already created):
int size = 5;
output.fill(QChar('\t'), size);
//'output' contains 5 tab characters
#include <QString>
QString s;
for(int i = 0; i < 3; ++i)
{
s << "dad";
}
this is what i have of the function so far. This is only the beginning of the problem, it is asking to generate the random numbers in a 10 by 5 group of numbers for the output, then after this it is to be sorted by number size, but i am just trying to get this first part down.
/* Populate the array with 50 randomly generated integer values
* in the range 1-50. */
void populateArray(int ar[], const int n) {
int n;
for (int i = 1; i <= length - 1; i++){
for (int i = 1; i <= ARRAY_SIZE; i++) {
i = rand() % 10 + 1;
ar[n]++;
}
}
}
First of all we want to use std::array; It has some nice property, one of which is that it doesn't decay as a pointer. Another is that it knows its size. In this case we are going to use templates to make populateArray a generic enough algorithm.
template<std::size_t N>
void populateArray(std::array<int, N>& array) { ... }
Then, we would like to remove all "raw" for loops. std::generate_n in combination with some random generator seems a good option.
For the number generator we can use <random>. Specifically std::uniform_int_distribution. For that we need to get some generator up and running:
std::random_device device;
std::mt19937 generator(device());
std::uniform_int_distribution<> dist(1, N);
and use it in our std::generate_n algorithm:
std::generate_n(array.begin(), N, [&dist, &generator](){
return dist(generator);
});
Live demo
I have recently come across with this problem,
you have to find an integer from a sorted two dimensional array. But the two dim array is sorted in rows not in columns. I have solved the problem but still thinking that there may be some better approach. So I have come here to discuss with all of you. Your suggestions and improvement will help me to grow in coding. here is the code
int searchInteger = Int32.Parse(Console.ReadLine());
int cnt = 0;
for (int i = 0; i < x; i++)
{
if (intarry[i, 0] <= searchInteger && intarry[i,y-1] >= searchInteger)
{
if (intarry[i, 0] == searchInteger || intarry[i, y - 1] == searchInteger)
Console.WriteLine("string present {0} times" , ++cnt);
else
{
int[] array = new int[y];
int y1 = 0;
for (int k = 0; k < y; k++)
array[k] = intarry[i, y1++];
bool result;
if (result = binarySearch(array, searchInteger) == true)
{
Console.WriteLine("string present inside {0} times", ++ cnt);
Console.ReadLine();
}
}
}
}
Where searchInteger is the integer we have to find in the array. and binary search is the methiod which is returning boolean if the value is present in the single dimension array (in that single row).
please help, is it optimum or there are better solution than this.
Thanks
Provided you have declared the array intarry, x and y as follows:
int[,] intarry =
{
{0,7,2},
{3,4,5},
{6,7,8}
};
var y = intarry.GetUpperBound(0)+1;
var x = intarry.GetUpperBound(1)+1;
// intarry.Dump();
You can keep it as simple as:
int searchInteger = Int32.Parse(Console.ReadLine());
var cnt=0;
for(var r=0; r<y; r++)
{
for(var c=0; c<x; c++)
{
if (intarry[r, c].Equals(searchInteger))
{
cnt++;
Console.WriteLine(
"string present at position [{0},{1}]" , r, c);
} // if
} // for
} // for
Console.WriteLine("string present {0} times" , cnt);
This example assumes that you don't have any information whether the array is sorted or not (which means: if you don't know if it is sorted you have to go through every element and can't use binary search). Based on this example you can refine the performance, if you know more how the data in the array is structured:
if the rows are sorted ascending, you can replace the inner for loop by a binary search
if the entire array is sorted ascending and the data does not repeat, e.g.
int[,] intarry = {{0,1,2}, {3,4,5}, {6,7,8}};
then you can exit the loop as soon as the item is found. The easiest way to do this to create
a function and add a return statement to the inner for loop.
i want to create a pattern in c++ that looks like a trianlge(or half a diamond)
using asteriscks: the pattern should have 1, 2, 3, 4, and end in 5 stars like this
*
**
***
****
*****
(but straight!)
my code is as follows:
-`#include
using namespace std;
int main()
{
int size;
cout<<"size:"<<endl;
cin>>size;
int blank=size/2;
int newsize=1;
for (int i=0; i<=size/2; i++)
{
for(int j=blank;j>0;j--)
cout <<" ";
blank--;
for(int j=newsize; j>0; j--)
cout <<"*";
newsize+=2;
cout <<endl;
}
return 0;
}
`
my only problem with it is that it displays 1, 3,and 5 stars like this.
*
***
*****
its just a minor problem but although i have changed different parts of the code
i dont seem to get it right.
any suggestions?
thanks
:)
I'm not sure what you mean by "but straight", so I'll just ignore that for now...
Start with blank the same value as size, so that you can decrement the value each time without having to decrement by a half:
int blank=size;
Loop up to size instead of size/2 to get more lines:
for (int i=0; i<=size; i++)
Decrement by two in the loop for spaces to get half the number of spaces:
for(int j=blank;j>0;j-=2)
Increase the size by one instead of two to get the slower increase:
newsize++;
That should produce the output that you showed.
Edit:
I tested this to be sure, and the output is:
*
**
***
****
*****
******
To get the exact output that you asked for, start with blank one less:
int blank=size - 1;
Did I get it right: you want to place some asterisks on borders of character places? If so, it isn't possible. Every asterisk (or any other symbol), when displayed in monospace fonts, will reside in a middle of a character place, like in a grid. You can place asterisks inside the cells, but you cannot place asterisks on the borders of the grid.
int NUMLINES = 5;
void display(int, char);
void main(){
for (int i=1; i<= NUMLINES; ++i){
display((NUMLINES + 1 - i), ' ');
display(( 2 * i - 1 ), '*');
cout << endl;
}
}
void display (int howmany, char symbol){
for (int i = 1; i<=howmany; ++i)
cout << symbol;
}