I'm getting problem with segmentation fault when trying to compile a C++ program, but not sure where the problem lies. I suspect that the problem lies with the .find() ..... could it be the iterator operator < and == which are the comparators for find() that is the issue? I hope that someone can point out to me where they think the problem lies.
The following is part of test01.cpp, where I run it to test the code and use print statements to find out where the problem is:
bool confirmEverythingMatches(const btree<long>& testContainer, const set<long>& stableContainer) {
cout << "Confirms the btree and the set "
"contain exactly the same values..." << endl;
for (long i = kMinInteger; i <= kMaxInteger; i++) {
cout << "Start of for-loop to find iterator for comparisons..." << endl;
if (stableContainer.find(i) != stableContainer.end()) {
cout << "can find i (" << i << ") in stableContainer!" << endl;
} else {
cout << "cannot find i (" << i << ") in stableContainer!" << endl;
}
cout << "In between finding i in stable and testContainers..." << endl;
if (testContainer.find(i) != testContainer.end()) {
cout << "can find i (" << i << ") in testContainer!" << endl;
} else {
cout << "cannot find i (" << i << ") in testContainer!" << endl;
}
cout << "Before assigning the find to boolean variables..." << endl;
bool foundInTree = (testContainer.find(i) != testContainer.end());
cout << "testContainer.find(i) != testContainer.end()" << endl;
bool foundInSet = (stableContainer.find(i) != stableContainer.end());
cout << "stableContainer.find(i) != stableContainer.end()" << endl;
if (foundInTree != foundInSet) {
cout << "- btree and set don't contain the same data!" << endl;
cout << "Mismatch at element: " << i << endl;
return false;
} else {cout << "foundInTree == foundInSet!!!" << i << endl;}
}
cout << "- btree checks out just fine." << endl;
return true;
}
} // namespace close
/**
* Codes for testing various bits and pieces. Most of the code is commented out
* you should uncomment it as appropriate.
**/
int main(void) {
// initialise random number generator with 'random' seed
initRandom();
cout << "after initRandom().." << endl;
// insert lots of random numbers and compare with a known correct container
btree<long> testContainer(99);
cout << "after specifying max node elements in testContainer.." << endl;
set<long> stableContainer;
cout << "after constructing stableContainer.." << endl;
insertRandomNumbers(testContainer, stableContainer, 1000000);
cout << "after inserting random numbers into testContainer and for success inserts, also into stableContainer.." << endl;
btree<long> btcpy = testContainer;
cout << "after copy assigning a copy of testContainer to btcopy.." << endl;
confirmEverythingMatches(btcpy, stableContainer);
cout << "after confirming everything internally matches between testContainer and stableContainer.." << endl;
return 0;
}
The output I get when running the program (No problem when compiling) is this:
Confirms the btree and the set contain exactly the same values...
Start of for-loop to find iterator for comparisons...
cannot find i (1000000) in stableContainer!
In between finding i in stable and testContainers...
ASAN:DEADLYSIGNAL
=================================================================
==7345==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000018 (pc 0x000108d132a8 bp 0x000000000000 sp 0x7fff56eee6f0 T0)
#0 0x108d132a7 in btree<long>::find(long const&) const (test01+0x1000022a7)
AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (test01+0x1000022a7) in btree<long>::find(long const&) const
==7345==ABORTING
Abort trap: 6
I also got this error when I tried to run it on another machine:
==29936==ERROR: AddressSanitizer failed to allocate 0x200000 (2097152) bytes of SizeClassAllocator32: 12
I found that when it goes into the find(), it will have the segmentation fault:
/**
* Identical in functionality to the non-const version of find,
* save the fact that what's pointed to by the returned iterator
* is deemed as const and immutable.
*
* #param elem the client element we are trying to match.
* #return an iterator to the matching element, or whatever the
* const end() returns if no such match was ever found.
*/
template<typename T> typename btree<T>::const_iterator
btree<T>::find(const T& elem) const {
std::cout << "CONST ITERATOR'S FIND" << std::endl;
Node *tmp_ = root_;
std::cout << "1" << std::endl;
while(true) {
std::cout << "2" << std::endl;
size_t i;
std::cout << "3" << std::endl;
// go through all elements from root to tail
for (i = 0; i < tmp_->__occupied_size_; ++i) {
std::cout << "4" << std::endl;
if (tmp_->__elem_[i] == elem) {
std::cout << "5" << std::endl;
// find the elem, return an iterator
return const_iterator(tmp_, i, this);
std::cout << "6" << std::endl;
} else if (tmp_->__elem_[i] > elem) {
std::cout << "7" << std::endl;
// elem is not in current Node, go to descendants
// for the elem.
if (tmp_->__descendants_ == nullptr) {
std::cout << "8" << std::endl;
return cend();
std::cout << "9" << std::endl;
} else {
std::cout << "10" << std::endl;
tmp_ = tmp_->__descendants_[i];
std::cout << "11" << std::endl;
break;
}
}
}
// handling boundaries cases
if (i == tmp_->__occupied_size_) {
std::cout << "12" << std::endl;
if (tmp_->__descendants_[i] == nullptr) {
std::cout << "13" << std::endl;
return cend();
std::cout << "14" << std::endl;
} else {
std::cout << "15" << std::endl;
tmp_ = tmp_->__descendants_[i];
}
}
}
}
The print statements for this find is:
CONST ITERATOR'S FIND
1
2
3
4
4
7
10
11
2
3
4
7
10
11
ASAN:DEADLYSIGNAL
Ok, so based on the implementation of this find function, I think the problem might be located in
if (tmp_->__descendants_ == nullptr) {
std::cout << "8" << std::endl;
return cend();
std::cout << "9" << std::endl;
} else {
std::cout << "10" << std::endl;
tmp_ = tmp_->__descendants_[i];
std::cout << "11" << std::endl;
break;
}
and then
// handling boundaries cases
if (i == tmp_->__occupied_size_) {
std::cout << "12" << std::endl;
if (tmp_->__descendants_[i] == nullptr) {
std::cout << "13" << std::endl;
return cend();
std::cout << "14" << std::endl;
} else {
std::cout << "15" << std::endl;
tmp_ = tmp_->__descendants_[i];
}
}
So, You are checking if tmp->__descendants_ is not null. If it is not, then you set tmp_ = tmp_->descendants_[i];
Note: you are just checking __descendants_ pointer to be null or not, you are not checking the __descendants_ [i] if it is null!
What if the tmp->__descendants_[i] is null (or gets out of the descendants array)?
If that value is null, then tmp_->occupied_size_ might give you segfault.
Note2: For some reason you are using same index "i" for iterating through __elem_ and __descendants_. I am not sure, how descendants are created, but it might be also a problem here.
This is why debuggers exist. Run your program in the debugger, let the program fail, and then the debugger will tell you where and why it's gone wrong.
It looks like you've got potentially a lot of code to trawl through, which no one here will really want to do as it's not a concise question.
Good luck!
Related
I am attempting to solve a problem to improve my C++ skills. I have come across some unusual behavior and I am not sure why it is happening.
I initially parsed the stdin and sorted it into a map with a key and a matching element (value). I then want to read a list of keys and output the element (value). However, for some of the key names it returns the correct value but for others it does not, but, if I hard code the intended key it works.
I know I am parsing correctly since the correct key and value are in the map as shown at the end of my output.
I assume it is an issue with reading stdin since the boolean str.compare("tag1.tag2~name") == 0 never evaluates to 0.
The code is as follows:
//'it' is the name of my map
//q = 3
for (int i = 0; i < q; i++)
{
getline(cin, str);
if (str.compare("tag1.tag2~name") == 0)
{
cout << "key is found" << endl;
}
else
{
cout << "'" << str << "'" << endl;
}
if (it.count(str) == 0)
{
cout << "Not Found!" << endl;
}
else
{
cout << it[str] << endl;
}
}
map<string, string>::iterator ptr;
cout << "\nThe map it is : \n";
cout << "\tKEY\tELEMENT\n";
for (ptr = it.begin(); ptr != it.end(); ++ptr) {
cout << '\t' << ptr->first
<<"\t" + ptr->second << "\n";
}
return 0;
The output is:
'tag1.tag2~name
Not Found!
'tag1~name
Not Found!
'tag1~value'
HelloWorld
The map it is :
KEY ELEMENT
tag1.tag2~name Name1
tag1~value HelloWorld
The input is :
tag1.tag2~name
tag1~name
tag1~value
Thank you! I have been struggling with this for a while.
For a school project I need to shuffle a vector with unique pointers.
However when I do this I get a read access violation error after some time.
I create the vector and then call the shuffle. This I do multiple times. I just create the vector with the values and shuffle it once and after a couple of times I get the read access violation error.
code
int RandomEngine::generateRandomInt(int minValue, int maxValue)
{
std::uniform_int_distribution<int> distribution(minValue, maxValue);
std::cout << "Random getal van " << minValue << " tot " << maxValue << std::endl;
return distribution(def_rand_engine);
}
void RandomEngine::shuffleCharacterCards(std::vector<std::unique_ptr<CharacterCard>>& cards)
{
// Succeeds once but with multiple swaps read access violation
//auto randomInt = generateRandomInt(0, cards.size() - 1);
//iter_swap(cards.begin() + randomInt, cards.begin());
// Read access violation
//for (int i = 0; i < cards.size(); i++)
//{
// std::swap(cards[i], cards[std::rand() % cards.size()]);
//}
// Read access violation
//std::shuffle(cards.begin(), cards.end(), std::mt19937{ def_rand_engine});
// Read access violation
//std::random_shuffle(cards.begin(), cards.end());
// Read access violation
//std::shuffle(cards.begin(), cards.end(), std::mt19937(std::random_device()()));
}
Other class where I call the shuffle from the static class
void CharacterCardStack::prepare()
{
std::cout << "Preparing CharacterCardStack..." << std::endl;
if(cards_.size() > 2)
{
// Shuffle the cards
RandomEngine::shuffleCharacterCards(cards_);
// Burn the first card
burnedCharacterCard_ = std::move(cards_[0]);
std::cout << "Burned charactercard: " << burnedCharacterCard_->getName() << std::endl;
cards_.erase(cards_.begin());
// Als de open kaart een koning is dan moet deze vervangen worden door een ander.
if(cards_[0]->getName() == "Koning")
{
turnedCharacterCard_ = std::move(cards_[1]);
}
else
{
turnedCharacterCard_ = std::move(cards_[0]);
}
std::cout << "Turned charactercard: " << turnedCharacterCard_->getName() << std::endl;
cards_.erase(cards_.begin());
}
else
{
std::cerr << "CharacterCardStack::prepare cards size is " << cards_.size() << std::endl;
throw std::exception("Error...");
}
for (const auto& c : cards_)
{
std::cout << "Other card: " << c->getName() << std::endl;
}
std::cout << "CharacterCardStack prepared" << std::endl;
}
You have flow in your logic, you move out either first or the second element based on condition:
if(cards_[0]->getName() == "Koning")
{
turnedCharacterCard_ = std::move(cards_[1]);
}
else
{
turnedCharacterCard_ = std::move(cards_[0]);
}
but then unconditionaly erase the first element:
cards_.erase(cards_.begin());
so you may end up with moved out pointers.
Simple fix could be:
if(cards_[0]->getName() == "Koning")
{
std::swap( cards_[0], cards_[1] );
}
turnedCharacterCard_ = std::move(cards_[0]);
std::cout << "Turned charactercard: " << turnedCharacterCard_->getName() << std::endl;
cards_.erase(cards_.begin());
this way it is easier to keep it correct and I would prefer use cards.front() instead of cards_[0], which is I think more readable in this case.
Below I have my two functions which are, when when insertItem calls findIndex producing a segmentation fault. For some reason this happens when the value is returned. (I will include the cout statements so that it is easy to see exactly where this error happens). I am trying to locate the index of a value which is not in the list so -1 should be returned but never does. The output is below.
template <class ItemType>
int SortedList<ItemType>::findIndex(ItemType item) {
cout << "Entering findIndex function" << endl;
int first = 0;
int last = length-1;
int middle;
bool found = false;
while(!found) {
middle = (first+last)/2;
cout << "In findIndex, this is middle: " << middle << " and this is the item: " << item << " and this is the length: " << length << endl;
if(info[middle] == item) {
cout << "In findIndex found is now true" << endl;
found = true;
}
else if(item < info[middle])
last = middle-1;
else// if(item > info[middle])
first = middle+1;
if(first > last)//else// if(first > last)
break;
}
cout << "About to exit and return value from findIndex function" << endl;
if(found == true) {
cout << "findIndex Function: the index of the found value was " << middle << endl;
return middle;
}
else {
cout << "findindex Function: -1 was returned" << endl;
return -1;
}
}
template <class ItemType>
void SortedList<ItemType>::insertItem(ItemType item) {
cout << "Inside insertItem function, length: " << length << endl;
if(findIndex(item) != -1)
cout << "**Item already in the list" << endl;
else if(length == Max_Items)
cout << "**There is no room in the list" << endl;
else {
cout << "before the try" << endl;
try{
cout << "This is length at the start of the insertItem function: " << length << endl;
if(length == 0) {//if the list is empty item becomes the first item in the list \
cout << "This is right after length==0 in insertItem function" << endl;
info[0] = item;//was this->inf...
length++;
cout << "This is length right after incrementing it up" << length << endl;
}
else {//its not the first item in the list
for(int i = 0; i <= length; i++) {
cout << "This is the length and i respectively right inside the for in insertItem" << length << " " << i << endl;
if(i == length) {
cout << "this is where i == length" << endl;
info[i] = item;
length++;
break;
}
if(info[i] < item)
continue;
//inserting the item where it needs to go
for(int p = length; p > i; p--) {//was >=
info[p] = info[p-1];
}
//item = info[i];
info[i] = item;
length++;
break;
}
}
}catch(...) {cout << "**insertItem failed" << endl;}
}
cout << "This is length at the end of the insert item function: " << length << endl;
}
output:
...
Inside insertItem function, length: 0
Entering findIndex function
In findIndex, this is middle: 0 and this is the item: Name: Eman ID: 81012 and this is the length: 0
About to exit and return value from findIndex function
findindex Function: -1 was returned
Segmentation fault (core dumped)
~$:
So even the print saying -1 was returned is hit but nothing ever gets back to the original function. I am not sure as to what could cause a seg fault in this area. Could this return do it?
The following loop:
for(int p = length; p > i; p--) {
info[p] = info[p-1];
probably writes to 1 index past the length of the array, because valid array indexes probably range from 0 to length - 1.
A write to an illegal memory location can corrupt the stack, and this is likely to manifest as a crash when returning from a function.
Still, you really need to start using a debugger.
i am just using cppcheck the code is working properly just cppcheck gives this errors.
void WorkerThread(WorkBuffer* m_buffer)
{
std::cout << "Thread : " << m_buffer->m_id << ".....Starting" << std::endl;
if (NULL == m_buffer)
std::cout << "Thread : " << m_buffer->m_id << "......work buffer is null" << std::endl;
while(!shut_down_flag)
{
int k = 0;
//Sleep(1);
SleepSystemUsec(100000);
std::cout << "Thread : " << m_buffer->m_id << "....in while loop" << std::endl;
} // of while(!shut_down_flag)
std::cout << "Thread : " << m_buffer->m_id << ".....Request from main thread so ending working thread ...." << std::endl;
};
error : : Possible null pointer dereference: m_buffer - otherwise it is redundant to check it against null.
if (NULL == m_buffer)
makes sure m_buffer is NULL, and then you derefence it with
std::cout << "Thread : " << m_buffer->m_id << "......work buffer is null" << std::endl;
^^^^^^^^^^^^^^^
this, which is only legal if m_buffer is not NULL (more precisely, only if it points to a correctly constructed WorkBuffer).
If NULL is a possible input for your function, you need to check for it before the very first dereference and then either make it point to something valid or leave the function without dereferencing.
Not only is your condition backwards:
if m_buffer is NULL:
do things that dereference m_buffer
(huh?!)
but you have no checks on any of the other output statements.
In this program, I am using template class, I have a header file and this is my main file. I am having trouble displaying the (".....") IndexOutOfBounds and displaying it on the screen.
#include "XArray.h"
#include <iomanip>
#include <string>
using namespace std;
template<class T>
void afriend ( XArray<T> );
int main()
{
XArray<double> myAD(18);
myAD.randGen(15, 100);
cout << myAD.getType() << endl;
cout << setprecision(1) << fixed << "\n\n Unsorted: " << myAD;
myAD.sort();
cout << "\n Now Sorted: " << myAD;
cout << "\n\n";
**try
{
cout << "A[-5] = " << setw(6) << myAD[-5] << endl;
}
catch(XArray<double>::IndexOutOfBound e)
{
e.print();
}
try
{
cout << "A[8] = " << setw(6) << myAD[8] << endl;
}
catch(XArray<double>::IndexOutOfBound e)
{
e.print();
}**
cout << "\n\n" << setprecision(2) << fixed;
cout << "Size = " << setw(6) << myAD.getSize() << endl;
cout << "Mean = " << setw(6) << myAD.mean() << endl;
cout << "Median = " << setw(6) << myAD.median() << endl;
cout << "STD = " << setw(6) << myAD.std() << endl;
cout << "Min # = " << setw(6) << myAD.min() << endl;
cout << "Max # = " << setw(6) << myAD.max() << endl;
return 0;
}
There is the Array.h file posted as a dropbox link
Array.h
The code for operator[] in Array.h is:
template <class T>
T XArray<T>::operator[] (int idx)
{
if( (idx = 0) && (idx < size) )
{
return Array[idx];
}
else
{
throw IndexOutOfBound();
return numeric_limits<T>::epsilon();
}
}
Although the question is somewhat obscure, give a try to these suggestions.
Firstly, it can happen that XArray<>::IndexOutOfBounds have no proper copy ctor. You can try catching by const reference to workaround that:
try
{
...
}
catch(const XArray<double>::IndexOutOfBound& e)
{
e.print();
}
Index operator in standard library containers does not check for bounds, there is a special getter that does the check called at(). If the XArray class is designed with standard library in mind, it could behave similarly.
However to get more adequate response you need to be more specific describing the trouble you are having.
I'm still wondering what exact question is.
However, I'm understanding the question is that how I can use 'catch' by using 'IndexOutOfBound'.
#include <exception>
#include <iostream>
using namespace std;
template <typename T>
class Array
{
private:
int m_nLength;
T *m_ptData;
public:
...
...
T& operator[](int nIndex)
{
//assert(nIndex >= 0 && nIndex < m_nLength);
if(nIndex < 0 || nIndex > m_nLength)
{
throw myex;
}
else
{
return m_ptData[nIndex];
}
}
//class definition for 'IndexOutOfBound'
class IndexOutOfBound: public exception
{
public:
virtual const char* print() const throw()
{
return "Exception occured 'Index Out Of Bound'";
}
}myex;
};
int main()
{
Array<double> arr(3);
try
{
arr[0] = 1;
//exception will occur here.
arr[4] = 2;
}
catch(Array<double>::IndexOutOfBound &e)
{
cout << e.print() << '\n';
}
return 0;
}
Here is no 'XArray.h', so I've written a sample array class for example.
The problem is in the operator[] function. The code idx = 0 sets idx to 0. So all of your calls to operator[] will return the first element, and therefore there is no out-of-bounds error unless the array is empty.
You probably meant to write if ( idx >= 0 && idx < size ).
BTW the throw aborts the function, it makes no sense to return after throw.