My code crashes at insert function (segmentation fault), it looks like 'List.last' behave as static but its not. Dont mind the rest of a code. I know the solution must be simple but it cracks my head. It was a long time science I coded anything
#include <iostream>
#include <string>
#include <cmath>
#include <iomanip>
using namespace std;
typedef int elementtype, position ;
const int maxlength=10;
struct List
{
elementtype elements[maxlength];
elementtype last;
};
position END(List l)
{
return(l.last+1);
}
position First(List l)
{
if (l.last>=0)
return(l.last);
else
return(END(l));
}
position Next(position p,List l)
{
return(l.elements[p+1]);
}
position Previous(position p,List l)
{
return(l.elements[p-1]);
}
position Locate(elementtype x, List l)
{ int i;
for(i=0;i<=maxlength;i++)
{
if(x==l.elements[i])
return(i);
else
return(END(l));
}
}
elementtype Retrieve(position p, List l)
{
return(l.elements[p]);
}
bool Insert(int x, position p, List &l)
{
int i;
if(l.last-1==maxlength)
return(false);
else
if((p>=0)&&(p<=maxlength))
{l.last++;
for(i=l.last;i>p;i--)
l.elements[i+1]=l.elements[i];
l.elements[p]=x;
return(true);}
else return(false);
}
bool Delete(position p, List &l)
{
int i;
if(p>0||p<l.last){
l.elements[i]=l.elements[i+1];
l.last=l.last-1;
return(true);}
else
if(p=l.last){
l.last=l.last-1;
return(true);}
else
return(false);
}
void print(List l)
{
position i=First(l);
while (i!=END(l))
{
cout<< Retrieve(i,l);
i=Next(i,l);
}
cout<<("\n");
}
int main(){
List l;
l.last=-1;
Insert(100,First(l),l);
print (l);
cout<<l.elements[0];
for (int i=0; i<3;i++)
Insert(i,First(l),l);
print (l);
Insert (20,Previous(END(l),l) ,l);
print(l);
Delete( Locate(20,l),l);
print(l);
return 0;}
Here in your Locate function
for(i=0;i<=maxlength;i++)
you have a problem as you are allowing access of index 10 in an array of length 10. Change to
for(i=0;i<maxlength;i++)
similarly here in Insert
if((p>=0)&&(p<=maxlength))
allows later access of index 10 at this line
l.elements[p]=x;
Currently you are accessing elements beyond the array limits. If an array is of size x you cannot access array[x] as indices are zero based.
Using a debugger would help you identify this.
Apart from the changes suggested by #mathematician1975 , one basic error is in the
print(List)
method.
When the statement i=Next(i,l); executes , it fetches a value from the List.elements array, which initially contains random values. So what comes in the variable i is a random index for the array which seems to be generating the segmentation fault.
Related
#include<iostream>
#include<vector>
using namespace std;
class Stack
{
public:
int top;
vector<int> v;
Stack(int size)
{
top=0;
cout<<"Enter the values"<<endl;
for(int i=0; i<size; i++)
{
int val;
cin>>val;
v.push_back(val);
top++;
}
}
void push(int val)
{
v.push_back(val);
top++;
}
int pop()
{
int x=v[top];
top--;
return x;
}
void disp()
{
for(int j=top; j<=0; j--)
cout<<v[j]<<' ';
}
};
int main()
{
Stack s(3);
int k=s.pop();
cout<<k;
return 0;
}
I am trying to learn the basics of OOP.
Here, my Stack constructor and push function are working fine, but there is a problem with the pop and disp functions.
I'm assuming that I am using an incorrect syntax to access the elements of a vector(maybe?). Can anyone tell me where I am going wrong?
Also, the value of k always comes out to be 0.
You can use the vector functions
int k = s.back();
s.pop_back();
cout << k;
more informationhttp://www.cplusplus.com/reference/vector/vector/back/
You have a off-by-one index error.
The way you have implemented your class, when there are N items in the stack, the value of top is N.
Hence, top is not a valid index to access the elements of v. You can use:
int pop()
{
int x=v[top-1];
top--;
return x;
}
or
int pop()
{
top--;
int x=v[top];
return x;
}
As some of the other answers say, you can use the built-in vector functions to do these things (see pop_back and back.
However, if you want to define your own, I would use the vector.at(index) function. Addressing the values with the index as you have works, but it doesn't do any bounds checking at() does. Which would solve your problem above where your index isn't correct for the zero-based indexing of a vector.
I just wrote a code to build a Huffman Tree using MinHeap. When testing I want to output its traversal result.
The algorithm is simple, but my code can't get the right answer. It's strange that the output was different when I set different breakpoints. For instance, it depends on if I set a break point in the loop, such as line 165 input_list.insert(*parent);.
The test input was
4 //number of nodes.
1 1 3 5 //weight of each node.
and the output when debugging it with a breakpoint in the loop is
5
10
1
2
1
5
3
that is correct. But when I just run it without debug, it even didn't have any output. Does anyone know how to explain it?
#include <iostream>
#include <vector>
using namespace std;
#define max_size 100
int sum=0;
class huffman_node
{
public:
int weight;
huffman_node* left_child;
huffman_node* right_child;
huffman_node(){}
huffman_node(int w, huffman_node* l, huffman_node* r):
weight(w),left_child(l),right_child(r) {}
};
vector <huffman_node> node_list;
class minheap
{
public:
minheap()
{
heap=new huffman_node [max_size];
current_size=0;
}
~minheap()
{
delete []heap;
}
void siftdown(int start, int m)
{
int i=start;
int j=2*i+1;
huffman_node temp=heap[i];
while(j<=m)
{
if(j<m && heap[j+1].weight<heap[j].weight)
{
++j;
}
if(temp.weight<=heap[j].weight)
{
break;
}
else
{
heap[i]=heap[j];
i=j;
j=2*i+1;
}
}
heap[i]=temp;
}
void siftup(int start)
{
int j=start;
int i=(j-1)/2;
huffman_node temp=heap[j];
while(j>0)
{
if(heap[i].weight<=temp.weight)
{
break;
}
else
{
heap[j]=heap[i];
j=i;
i=(j-1)/2;
}
heap[j]=temp;
}
}
bool insert(const huffman_node& input)
{
if(current_size==max_size)
{
cout<<"minheap full"<<endl;
return false;
}
heap[current_size]=input;
siftup(current_size);
++current_size;
return true;
}
bool remove_min(huffman_node& output)
{
if(!current_size)
{
cout<<"minheap empty"<<endl;
return false;
}
output=heap[0];
heap[0]=heap[current_size-1];
--current_size;
siftdown(0,current_size-1);
return true;
}
private:
huffman_node* heap;
int current_size;
};
void route_length(huffman_node* &root,int depth)
{
if(root!=NULL)
{
// if(root->left_child==NULL&&root->right_child==NULL)
// {
// sum+=depth*root->weight;
// }
route_length(root->left_child,depth+1);
cout<<root->weight<<endl;
route_length(root->right_child,depth+1);
}
else
{
return;
}
}
int main()
{
minheap input_list;
int n;
cin>>n;
for(int i=0;i<n;++i)
{
int key;
cin>>key;
huffman_node input(key,NULL,NULL);
input_list.insert(input);
cin.get();
}
huffman_node* root;
for(int i=0;i<n-1;++i)
{
huffman_node* parent;
huffman_node out1;
huffman_node out2;
input_list.remove_min(out1);
input_list.remove_min(out2);
node_list.push_back(out1);
node_list.push_back(out2);
parent=new huffman_node(out1.weight+out2.weight,&node_list[node_list.size()-2],&node_list[node_list.size()-1]);
input_list.insert(*parent);
root=parent;
}
route_length(root,0);
// cout<<sum<<endl;
return 0;
}
The problem is that you are using pointers to elements of a vector<huffman_node> and storing these in your data structure (i.e. left and right members of the huffman_node object).
The thing that is randomly killing your program is that std::vector moves values around in memory when you append to it. The contents of the elements of the vectors are preserved, but the location is not. Once it moves the elements, the memory where the vector used to be can be overwritten by whatever (i.e. gdb needs heap memory too) and now the pointers are pointing to garbage.
As a quick sanity check, you can make your code not crash by reserving space in your node_list by calling
node_list.reserve(max_size*2);
in the beginning of main. This is not the right way of developing this piece of code further, but should illustrate the problem.
It would be better if your node_list was a vector<huffman_node*> instead. Or if you changed the left/right members to be vector indices instead of pointers.
#include <vector>
#include <iostream>
using namespace std;
void SubSetNum(bool * select, int*a, int selectk, int k, int selectn, int n )// depthk to
{
if(k>n) return;
if(selectn==n)
{
if(selectk==k)
{
for(int i=0;i<n;i++)
if(select[i]==true)
cout<<a[i];
cout<<endl;
}
return;
}
select[selectk]=false;
SubSetNum(select,a,selectk,k,selectn+1,n);
select[selectk]=true;
SubSetNum(select,a,selectk+1,k,selectn+1,n);
}
int main()
{
int k=3;
int n=5;
int a[]={1,5,8,10,13};
//while(cin>>k)
{
bool *select=new bool[n];
memset(select,0,sizeof(bool)*n);
SubSetNum(select,a,0,k,0,n);
delete []select;
}
return 0;
}
This a question, that I want to get k elements from n elements set.
But it prints out incorrect answer? I am always confused when I design recursive algorithms...Especially the parameter of functions, if or not return value, and so on, thus I always try to forcely remember the code in textbook.
Your mistake is here:
select[selectk]=false;
...
select[selectk]=true;
It should be this:
select[selectn]=false;
...
select[selectn]=true;
I believe the cause of the mistake was a failure to remember what the variables represent. The variable selectn is the index of the element being included or excluded. The variable selectk is the number of elements already included. It does not make sense to use selectk as an index into a.
#ifndef BINARY_TREE_H
#define BINARY_TREE_H
#include<iostream>
#include<vector>
using namespace std;
class Binary_Tree;
static int levelCount=0;
extern vector<vector<Binary_Tree*>> vec;
extern vector<Binary_Tree*> tempVec;
class Binary_Tree
{
public:
Binary_Tree()
{
childNum=0;
data=0;
level=0;
prev=NULL;
next[0]=NULL;
next[1]=NULL;
};
Binary_Tree(int d)
{
childNum=0;
data=d;
level=0;
prev=NULL;
next[0]=NULL;
next[1]=NULL;
levelCount++;
}
void insert_node(int,int,int);
int get_level();
int get_childCount();
friend int set_childNum(Binary_Tree*);
private:
int childNum;
int data;
int level;
Binary_Tree *prev;
Binary_Tree *next[2];
};
#endif // BINARY_TREE_H
Here is the implementation file
#include<iostream>
#include<cmath>
#include "Binary_Tree.h"
using namespace std;
void Binary_Tree::insert_node(int lev, int d, int sib)
{
if(vec.empty())
{
cout<<"You Have to create Root first";
}
else
{
if(set_childNum(vec[lev][sib-1])==0)
{
cout<<"Child cant be created parent Node already has two childs.";
}
else
{
childNum=set_childNum(vec[lev][sib-1]);
data=d;
level=lev+1;
prev=vec[lev][sib];
next[0]=NULL;
next[1]=NULL;
tempVec.clear();
for(int i=0; i<pow(2,(lev+1)); i++)
{
if(i==childNum-1)
{
tempVec.push_back(this);
}
else
tempVec.push_back(vec[lev][i]);
}
vector<vector<Binary_Tree*>>::iterator itr=vec.begin()+(lev+1);
vec.erase(itr);
vec.insert(itr,tempVec);
}
}
}
int set_childNum(Binary_Tree *lstNdAdr)
{
if(lstNdAdr->get_childCount()==0)
return 1;
else if(lstNdAdr->get_childCount()==1)
return 2;
else
return 0;
}
int Binary_Tree::get_level()
{
return level;
}
int Binary_Tree::get_childCount()
{
if(next[0]==NULL)
{
return 0;
}
else if(next[0]!=NULL && next[1]==NULL)
{
return 1;
}
else
{
return 2;
}
}
MAIN.cpp
#include <iostream>
#include<cmath>
#include"Binary_Tree.h"
using namespace std;
vector<vector<Binary_Tree*>> vec;
vector<Binary_Tree*> tempVec;
int main()
{
Binary_Tree tree;
here:
cout<<"Enter your Choice:1.Create Root Of Tree\n"
<<"2.Insert node\n"<<endl;
int choice;
cin>>choice;
switch(choice)
{
case 1:
{
int d;
cout<<"Enter Data to insert: ";
cin>>d;
Binary_Tree treeDummy(d);
tree=treeDummy;
tempVec.push_back(&tree);
vec.push_back(tempVec);
}
break;
case 2:
{
int lev;
int sibbling;
int d;
cout<<"Enter at which level and data and parent's sibling-no.: ";
cin>>lev;
cin>>d;
cin>>sibbling;
if(sibbling>pow(2,lev))
cout<<"Illegal Sibbling Number."<<endl;
else
tree.insert_node(lev,d,sibbling);
}
break;
}
int x;
cin>>x;
if(x==5)
{
cout<<endl<<endl;
goto here;
}
return 0;
}
in above code i am trying to create a binary tree type structure which can be manipulated and traversed dynamically that is any node can be inserted and can be removed at run time (although its incomplete because i am stuck at a problem). While pushing back the tempVec vector the code produces a segmentation fault and i am also doubtful in passing the object stored in vetcor> vec to the functions in the implementation (I am new to Stl and first time dealing with vector of vectors containing pointer to the class types)
The nested vector's entries are only filled if i is set to 1. But you attempt to access its element [0][0] regardless. You have out of bounds access when i is not 1.
There are numerous problems present in your code, that and combined with the poor style and formatting makes it not so fun to debug.
Binary_Tree treeDummy(d);
tree = treeDummy;
tempVec.push_back(&tree);
I'm not sure what you're trying to do here but the above looks wrong. You are shallow copying treeDummy's data over to tree. You'll lose the link to whatever child node tree points to. Afterwards you're pushing that same tree instance into your temporary vector. That means all the elements in your vector ends up pointing to the local variable tree in main. So even if no segfault occurred you would run into aliasing problems since they all refer to the same tree object and not a separate unique BinaryTree instance.
vector< vector<Binary_Tree*> >::iterator itr=vec.begin()+(lev+1);
vec.erase(itr);
vec.insert(itr,tempVec);
Your BinaryTree::insert_node is using an invalidated iterator after performing erase which is undefined behavior.
childNum = set_childNum(vec[lev][sib-1]);
// ...
prev = vec[lev][sib];
The above can access an out-of-bound index in your vector. eg. You push_back a tempVec with only 1 element in it and then call insert_node with sib = 1.
// ...
if(x == 5)
{
cout<<endl<<endl;
goto here;
}
The use of goto is also completely unnecessary here and should be replaced with a traditional while loop that checks for condition != 5.
The higher level problem in your program, however, is that there's no clear constraints and invariants in its design. What assumptions and preconditions do each of those functions need to work? Why use vectors to hold BinaryTree nodes when the class itself should be dealing with that. You should get the overall design sorted out first, otherwise you'll just play whack-a-mole as other bugs crop up.
I'm implementing a simple priority queue in C++.
However when it runs, it prints out gibberish numbers.
Am I somehow trying to access invalid entries in the array in my code?
Below is the code.
Also, is my "remove" function somehow not doing its job? Conceptually, shall I be putting null into the first entry and return whatever was just erased?
Thanks.
[Priority.h]
#ifndef Priority_h
#define Priority_h
class Priority
{
public:
Priority(void);
Priority(int s);
~Priority(void);
void insert(long value);
long remove();
long peekMin();
bool isEmpty();
bool isFull();
int maxSize;
long queArray [5];
int nItems;
private:
};
#endif
[Priority.cpp]
#include <iostream>
#include <string>
#include <sstream>
#include <stack>
#include "Priority.h"
using namespace std;
Priority::Priority(void)
{
}
Priority::Priority(int s)
{
nItems = 0;
}
Priority::~Priority(void)
{
}
void Priority::insert(long item)
{
int j;
if(nItems==0) // if no items,
{
queArray[0] = item; nItems++;
}// insert at 0
else // if items,
{
for(j=nItems-1; j=0; j--) // start at end,
{
if( item > queArray[j] ) // if new item larger,
queArray[j+1] = queArray[j]; // shift upward
else // if smaller,
break; // done shifting
} // end for
queArray[j+1] = item; // insert it
nItems++;
} // end else (nItems > 0)
}
long Priority::remove()
{
return queArray[0];
}
long Priority::peekMin()
{
return queArray[nItems-1];
}
bool Priority::isEmpty()
{
return (nItems==0);
}
bool Priority::isFull()
{
return (nItems == maxSize);
}
int main ()
{
Priority thePQ;
thePQ.insert(30);
thePQ.insert(50);
thePQ.insert(10);
thePQ.insert(40);
thePQ.insert(20);
while( !thePQ.isEmpty() )
{
long item = thePQ.remove();
cout << item << " "; // 10, 20, 30, 40, 50
} // end while
cout << "" << endl;
system("pause");
}
Here is one error:
for(j=nItems-1; j=0; j--) // start at end,
^ this is assignment, not comparison.
I am also not convinced that there isn't an off-by-one error in
queArray[j+1] = item; // insert it
Finally, your default constructor fails to initialize nItems.
There could be further errors, but I'll stop at this.
I agree with the other answers here, but I would add this:
Your "Remove" method isn't actually removing anything - it is just returning the first element - but it doesn't do anything to the array itself.
Edited to say that your insert method needs some work - it may or may not write over the end of the array, but it is certainly confusing as to what it is doing.
Try initializing your queue array in the constructor.