CODEWITHSUNDEEP
c++memory-leaksvalgrindnew-operatordelete-operator
sestus
sestus

Reputation: 1927

Valgrind errors when delete is done in another class

I am trying to test c++ performance when object locality is low, thus I am trying to allocate a large amount of memory that has many "dead objects". I am going to benchmark the "live objects" when there are many "dead ones" between them.

For that purpose I defined A simple LinkedList:

#include "LinkedList.hpp"
#include <iostream>
#include <string>

LinkedList::LinkedList() {
    this->first = NULL;
    this->last = NULL;
    this->size = 0;
}

void LinkedList::add(node_t *node) {
    if (!last) {
        first = node;
        last = first;
        size++;
        return;
    }
    last->next = node;
    last = last->next;
    size++;
}


void LinkedList::deleteFirst() {
    if (first == NULL || size <= 0) {
        std::cout << "Cannot Delete from empty list" << std::endl;
        return;
    }
    node_t* oldfirst = first;
    first = first->next;
    delete oldfirst;
    size--;
}

Header File:

#ifndef LINKEDLIST_HPP
#define LINKEDLIST_HPP

class node_t {
    public:
        node_t *next;
};


class LinkedList {

    public:
        LinkedList();
        void add(node_t*);
        void deleteFirst();
        node_t *first;
        int size;
    private:
        node_t *last;
};

#endif

While trying to experiment, I ve noticed that valgrind shows that I have some memory leaks. I am pretty sure that I am deleting every allocated object though. Here is my main:

#include "LinkedList.hpp"
#include <ctime>
#include <cstdlib>

bool doConnect() {
    int  r;
    r = rand();

    return ((r % 2) == 1);
}

int main() {

    srand(time(NULL));
    int size = 100000;
    int i = 0;
    LinkedList *node_list = new LinkedList();
    LinkedList *dead_node_list = new LinkedList();


    for (i=0; i < size; i++) {
        node_t *new_node = new node_t();
        if (doConnect()) {
            node_list->add(new_node);
        }
        else {
            dead_node_list->add(new_node);
        }
    }


    for (i=0; i < dead_node_list->getSize(); i++)
            dead_node_list->deleteFirst();

    for (i=0; i < node_list->getSize(); i++)
            node_list->deleteFirst();

    delete node_list;
    delete dead_node_list;



    return 0;
}

And here is valgrind's output:

==15291== Memcheck, a memory error detector
==15291== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==15291== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==15291== Command: ./main
==15291== 
==15291== 
==15291== HEAP SUMMARY:
==15291==     in use at exit: 199,720 bytes in 24,965 blocks
==15291==   total heap usage: 100,002 allocs, 75,037 frees, 800,048 bytes allocated
==15291== 
==15291== LEAK SUMMARY:
==15291==    definitely lost: 16 bytes in 2 blocks
==15291==    indirectly lost: 199,704 bytes in 24,963 blocks
==15291==      possibly lost: 0 bytes in 0 blocks
==15291==    still reachable: 0 bytes in 0 blocks
==15291==         suppressed: 0 bytes in 0 blocks
==15291== Rerun with --leak-check=full to see details of leaked memory
==15291== 
==15291== For counts of detected and suppressed errors, rerun with: -v
==15291== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

Am I missing something obvious?

I compile my code with: g++ -Wall -g LinkedList.cpp main.cpp -o main

Upvotes: 0

Views: 224

Answers (1)

JSF
JSF

Reputation: 5311

What did you think the variable i is doing in this code?

for (i=0; i < dead_node_list->getSize(); i++)
        dead_node_list->deleteFirst();

The size should be going down, so with i going up, you only delete half the original nodes.

You didn't show all the code, so I have to assume the missing parts are ordinary. But with that assumption, the above code should have been:

while ( dead_node_list->getSize())
        dead_node_list->deleteFirst();

and similar for the other list.

Upvotes: 2

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