Getting a segfaulr and I can't figure out why

[stealthy12341]

Title. I don't know why this is happening but I am getting a segfault saying free(): invalid size
error is
__GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
51 ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.

I will be splitting my files with *************************************

#include <iostream>
#include <cctype>
#include <cstring>
#include <fstream>
using namespace std;

// These are my non Tech functions.
void welcome();
int how_many_in_file();

struct tech_list
{
        char *tech_name;
        char *tech_desc;
        float cost;
        char *pro;
        char *con;
        float rating;
};

class Tech
{
        public:
                Tech(int howmany, int howmany_filein); // This is my constructor.
                ~Tech(); // This is my destructor.
                Tech file_in(); // This reads in from the file.
                void read_out(int howmany); // This reads out to the file.
                void input(); // This is my function for user input.
                void edit_name(int x); // This is an extension of my search function, for editting the name.
                void edit_desc(int x);
                void edit_cost(int x);
                void edit_pro(int x);
                void edit_con(int x);
                void edit_rating(int x);
                void display(int j); // This is my display all function.
                void search(); // This searches for the item name that the user wants to edit.
                void display_pro(); // This displays the pro.
                void display_con();// This displays the con.

        private:
                tech_list *object; // A pointer of the type tech_list.
                int size; // This is for holding my maximum number of items.
                int num_items; // This is a counter for making sure I am inputting only after the read in items.
};

*************************************************************************

#include "class.h"


int main()
{
        welcome();
        int selection;
        int howmany;
        char again;
        cin >> howmany; cin.ignore();
        int howmany_filein = how_many_in_file();
        howmany = howmany + howmany_filein;
        Tech object(howmany, howmany_filein);
        object.file_in();

        for(int i = howmany_filein; i < howmany; i++)
        {
                cout << "We are working with item #: "
                        << i + 1 << endl;
                object.input();
        }


        do{
                cout << "Please enter 1 to display all, 2 to edit an item, 3 to display the benefit of an item, and 4 to display the con of an item." << endl;
                cin >> selection; cin.ignore();

                if(selection == 1)
                {
                        for(int j = 0; j < howmany; j++)
                        {
                                object.display(j);
                        }
                }

                if(selection == 2)
                {
                        object.search();
                }

                if(selection == 3)
                {
                        object.display_pro();
                }

                if(selection == 4)
                {
                        object.display_con();
                }

                cout << "to continue enter y, to end the program enter n." << endl;
                cin >> again; cin.ignore();
        }while(again == 'y');
        object.read_out(howmany);
        return 0;
}

**************************************************************************

#include "class.h"

// This is my constructor.
Tech::Tech(int howmany, int howmany_filein)
{
        object = new tech_list[howmany]; // This initializes my object pointer of type tech_list (my struct) to point to a new array of type tech_list of size howmany.
        // Which is the sum of the number of items read in from our data.txt, and however many items the user indicated they wanted to add.
        size = howmany; // I am setting the maximum size, to be used so that I can stop my functions from inputting past my allocated memory.
        num_items = howmany_filein;  // num_items is a counter, that takes in the number of items read in so it doesn't write over any information we wanted to be saved in our data.txt
}

// This is my deconstructor, this deletes the new objects when we are done with them and have already saved them via external data files.
Tech::~Tech()
{
        delete object;
}

// This function reads in the first part of the external data file, an integer that represents the number of items that are saved in our external data file.
int how_many_in_file()
{
        ifstream filein;
        filein.open("data.txt");
        if(filein)
        {
                int size_temp;
                filein >> size_temp;
                filein.ignore(100, '\n');
                return size_temp;
        }
        filein.close(); // Closing the file so we can work with it later.
}

// This function is for reading in the data from our external data file.
Tech Tech::file_in()
{
        ifstream filein;
        filein.open("data.txt");
        if(filein) // If we're in the file it executes.
 {
                int size_temp;
                filein >> size_temp;
                filein.ignore(100, '\n'); // This is to move past the number at the start, because we have already used that in a seperate function. See function "how_many_in_file"


                int i= 0;
                char temp[200];

                while(filein && !filein.eof())
                {
                        // This reads in from the file into temp, and dynamically allocates our pointers within the struct tech_list and copies the temp into them.
                        filein.get(temp, 200, '|'); filein.ignore(200, '|');
                        object[i].tech_name = new char[strlen(temp)+1];
                        strcpy(object[i].tech_name, temp);

                        filein.get(temp, 200, '|'); filein.ignore(200, '|');
                        object[i].tech_desc = new char[strlen(temp)+1];
                        strcpy(object[i].tech_desc, temp);

                        filein >> object[i].cost; filein.ignore(100, '|'); // Like our input function, cost and rating are not pointers and do not need to be dynamically allocated.

                        filein.get(temp, 200, '|'); filein.ignore(200, '|');
                        object[i].pro = new char[strlen(temp)+1];
                        strcpy(object[i].pro, temp);

                        filein.get(temp, 200, '|'); filein.ignore(200, '|');
                        object[i].con = new char[strlen(temp)+1];
                        strcpy(object[i].con, temp);

                        filein >> object[i].rating; filein.ignore(100, '\n');
                        ++i; // As we read from the next part of the file, we increment i to save the next line of information to the next item.
                        filein.peek(); // This peeks to the next line and makes sure we aren't hitting the end of the file.

                }
                filein.close(); // Closing the file so we can work with it later.
        }
}

// This function writes the items into an external data file "data.txt".
void Tech::read_out(int howmany)
{

        ofstream fileout("data.txt", ios::in);

        if(!fileout)
        {
                return; // If we're not accessing the file, return.
        }

        fileout << howmany << endl;
        for(int j = 0; j < howmany; ++j)
        {
                fileout << object[j].tech_name << "|"; // Write the information of object tech_name at index "j".
                fileout << object[j].tech_desc << "|";
                fileout << object[j].cost << "|";
                fileout << object[j].pro << "|";
                fileout << object[j].con << "|";
                fileout << object[j].rating << endl; // Ends the line, indicating a new item.
 }
        fileout.close(); // Closes the file.
}

Any help would be very much appreciated, I got some help with classes on here and I was able to get it working earlier, but I tried to mess with main to add something else and it stopped working. Also I took out some of the input functions, they work fine I just didn't want to go over the character limit.

[salem c]

> object = new tech_list[howmany];
If you allocate an array of object, you MUST use

delete [] object;

But you also need

for ( int i = 0 ; i < howmany ; i++ ) {
  delete [] object[i].tech_name;
  // ditto for all the other elements you new'ed.
}

[stealthy12341]

Awesome thank you for the feedback, I just incorporated that into my deconstructor. I'm still having trouble figuring out why it is giving me the free(): invalid size error though, if you've got any thoughts I'd love to hear them, thanks!

[salem c]

Because underneath all the gloss that C++ gives you, there is still a need to allocate memory via one means or another.

Which in this instance means that at the bottom of the call chain, it's just C-style malloc and free.
But you never notice this detail until it all blows up.

[stealthy12341]

So how do I make sure that it is allocating memory? I thought I was doing that when I initialized my variables, and within my constructor

[salem c]

You've been allocating memory just fine all along.

It was your destructor that was the issue.

[stealthy12341]

So my destructor is

Tech::~Tech();
{
  for(int i = 0; i  < size; i++)
        {
                delete [] object[i].tech_name;
                delete [] object[i].tech_desc;
                delete [] object[i].pro;
                delete [] object[i].con;
        }
        delete [] object;
}

but this isn't solving my free(); invalid size error

[salem c]

> while(filein && !filein.eof())
You also need to be checking

i < num_items
Eg.
while ( i < num_items && !filein.eof())

> for(int i = 0; i < size; i++)
Is it size, or is it num_items ?


As it stands, your tech_list contains garbage pointers when you create it.

So maybe default-ctor which initialises all the pointers to NULL.
Because deleting null is actually harmless.

struct tech_list
{
        char *tech_name;
        char *tech_desc;
        float cost;
        char *pro;
        char *con;
        float rating;
        tech_list() : tech_name(0), tech_desc(0), pro(0), con(0) { }
};