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Aborted (core dumped)?

Brian Justice (25)
Alright so I have this code that compiles nicely but when it outputs I get these messages that I have no idea wtf is going on. Could someone help me with whats going on?

Output:

*** glibc detected *** ./a.out: free(): invalid pointer: 0xb76617b4 ***
======= Backtrace: =========
/lib/i386-linux-gnu/libc.so.6(+0x73e42)[0xb7533e42]
/usr/lib/i386-linux-gnu/libstdc++.so.6(_ZdlPv+0x1f)[0xb772d51f]
/usr/lib/i386-linux-gnu/libstdc++.so.6(_ZNSs4_Rep10_M_destroyERKSaIcE+0x1b)[0xb771499b]
/usr/lib/i386-linux-gnu/libstdc++.so.6(+0x909dc)[0xb77149dc]
/usr/lib/i386-linux-gnu/libstdc++.so.6(_ZNSs6assignERKSs+0x98)[0xb7716478]
/usr/lib/i386-linux-gnu/libstdc++.so.6(_ZNSsaSERKSs+0x23)[0xb77164c3]
./a.out[0x8048e51]
./a.out[0x8049594]
./a.out[0x8048fb8]
/lib/i386-linux-gnu/libc.so.6(__libc_start_main+0xf3)[0xb74d94d3]
./a.out[0x8048d21]
======= Memory map: ========
08048000-0804a000 r-xp 00000000 07:00 785817 /home/brianjustice/CS/a.out
0804a000-0804b000 r--p 00001000 07:00 785817 /home/brianjustice/CS/a.out
0804b000-0804c000 rw-p 00002000 07:00 785817 /home/brianjustice/CS/a.out
0817b000-0819c000 rw-p 00000000 00:00 0 [heap]
b7492000-b7494000 rw-p 00000000 00:00 0
b7494000-b74be000 r-xp 00000000 07:00 267853 /lib/i386-linux-gnu/libm-2.15.so
b74be000-b74bf000 r--p 00029000 07:00 267853 /lib/i386-linux-gnu/libm-2.15.so
b74bf000-b74c0000 rw-p 0002a000 07:00 267853 /lib/i386-linux-gnu/libm-2.15.so
b74c0000-b765f000 r-xp 00000000 07:00 267780 /lib/i386-linux-gnu/libc-2.15.so
b765f000-b7661000 r--p 0019f000 07:00 267780 /lib/i386-linux-gnu/libc-2.15.so
b7661000-b7662000 rw-p 001a1000 07:00 267780 /lib/i386-linux-gnu/libc-2.15.so
b7662000-b7666000 rw-p 00000000 00:00 0
b7666000-b7682000 r-xp 00000000 07:00 263235 /lib/i386-linux-gnu/libgcc_s.so.1
b7682000-b7683000 r--p 0001b000 07:00 263235 /lib/i386-linux-gnu/libgcc_s.so.1
b7683000-b7684000 rw-p 0001c000 07:00 263235 /lib/i386-linux-gnu/libgcc_s.so.1
b7684000-b775c000 r-xp 00000000 07:00 916057 /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16
b775c000-b775d000 ---p 000d8000 07:00 916057 /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16
b775d000-b7761000 r--p 000d8000 07:00 916057 /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16
b7761000-b7762000 rw-p 000dc000 07:00 916057 /usr/lib/i386-linux-gnu/libstdc++.so.6.0.16
b7762000-b7769000 rw-p 00000000 00:00 0
b7778000-b777b000 rw-p 00000000 00:00 0
b777b000-b777c000 r-xp 00000000 00:00 0 [vdso]
b777c000-b779c000 r-xp 00000000 07:00 267748 /lib/i386-linux-gnu/ld-2.15.so
b779c000-b779d000 r--p 0001f000 07:00 267748 /lib/i386-linux-gnu/ld-2.15.so
b779d000-b779e000 rw-p 00020000 07:00 267748 /lib/i386-linux-gnu/ld-2.15.so
bf968000-bf989000 rw-p 00000000 00:00 0 [stack]
Aborted (core dumped)

My code is
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#include <iostream>
#include <string>
#include <fstream>
#include <cstdlib>
#include <stdio.h>
#include <stdlib.h>
#include <sstream>
using namespace std;

class Queue;

class City {
  friend class Queue;
  friend class DataOrganizer;
  Queue *q;       // List of cities this one is directly connected to
  City *from;    // To trace a path back to origin
  string name;    // Name of the city
  bool mark;    // false=unmarked, true=visiting or done
  City *nextOne;

public:
  City ();
  void setName (string theName);
  void neighbor (City *c);
  City *next ();
  void setMark();
  void setFrom(City* g);
  void displayBestRoute ();
  bool checkMark();

  //~City () { delete q; if (name != NULL) delete name; }
};

//################## Queue class ######################
class Queue {
  friend class City; 
  City *tail;
public:
  Queue() { tail = NULL;  }

  void enqueue(City *t) {
    if (t == NULL) return;
    if (tail == NULL) {
      tail = new City();
      tail->setName(t->name);
      tail->nextOne = tail; }
    else {
      City *h = new City();
      h->setName(t->name);
      h->nextOne = tail->nextOne;
      tail->nextOne = h;
      tail = h;
    }
  }

  City *dequeue() {
    if (tail == NULL) return NULL;
    City *ptr = tail->nextOne;
    if (ptr != tail) tail->nextOne = ptr->nextOne; 
    else tail = NULL;
    City *t = ptr;
    delete ptr;
    return t; 
  }

  int isEmpty() {  return tail == NULL;  }
}; 

City:: City () { q = new Queue();  from = NULL;  mark = false;  name = ""; nextOne = NULL; }
void City::setName (string theName) { name = theName; }
void City::neighbor (City *c) { q->enqueue(c); }
City *City::next () { return (City *)q->dequeue(); }
void City::setMark() { mark = true; }
void City::setFrom(City* g) { from = g; }
bool City::checkMark() {
  if (mark == true) return true;
  if (mark == false) return false;
}
void City::displayBestRoute () {     // displays route back to city of origin
    cout << name << " ";
    while (from != NULL) {
      cout << from->name << " ";
      from = from;
    }
}


/////  Organizes Data
class DataOrganizer {
  int count;      // Counts the number of cities
  string name;    // accepts input from the file
  City **cities;

 public:
  DataOrganizer () { count = 0; }

  void readInput (char *filename) {
    fstream *fin = new fstream(filename, ios::in);
    while (true) {
      string buffer;
      *fin >> buffer; 
      if (buffer.compare("-") == 0) break;
      count ++; }
    fin->close();  
    fin->clear();
    
    string tok;
    cities = new City*[count];
    fin->open(filename, ios::in);
    size_t mark = fin->tellg(); 
    for (int i=0; *fin>>tok && tok != "-"; i++) cities[i]->setName(tok);
    for (int i=0; i < count; i++) {
      for (int j=0; *fin>>tok && tok != "-"; j++) { 
	int n;
	istringstream(tok) >> n;
	cities[i]->neighbor(cities[n]); 
      }  
    }
    fin->close();
    fin->clear();
  }

  City *getOrigin() { return cities[0]; }
  City *getDestination() { return cities[count]; }
};

int main (int argc, char **argv) {
  if (argc != 2) {
    cout << "Usage: " << argv[0] << " \n";
    exit(0);
  }

  DataOrganizer dao;
  dao.readInput(argv[1]);

  // Set origin and destination cities
  City *origin = dao.getOrigin();
  City *destin = dao.getDestination();
  City *city;
  Queue *q = new Queue ();  // Simulate simultaneity

  origin->setMark();
  q->enqueue(origin);
  while (!q->isEmpty()) {
    City *current = (City*) q->dequeue();
    while((city = current->next()) != NULL) {
      if (city == destin) {
	city->setFrom(current);
	cout << "Origin: " << origin << endl;
	cout << "Destin: " << destin << endl;
	city->displayBestRoute();
	return 0;
      }
      if (!(city->checkMark() == true)) {
	city->setMark();
	city->setFrom(current);
	q->enqueue(city);
      }
    }
  }
  cout << "No Route Between Selected Cities\n";
}
Last edited on
Moschops (7244)
Somewhere you are deleteing a pointer that you shouldn't be.

You can easily find where by compiling your code with the switch -g and then running your code under gdb, for example

gdb ./a.out

and then

run <usual command line options here>

When it crashes, you will be told the offending line and you can interrogate the variables with the print command.

Brian Justice (25)
Yes I know about this but I dont know how to read all the messages it gives. I've never really used a debugger before
Moschops (7244)
Yes I know about this but I dont know how to read all the messages it gives

Well then it's time to learn. At the very least build it with debug symbols ( -g ). You'll get a line number containing the code that caused the crash.
Brian Justice (25)
i usally alway compile it with -g . then i did gdb ./a.out, then run hops.10.dat (which is the file that I want it to read) its printed quite of bit of messages and from there its just confusing. Ive read through it a bit and really not seeing anything that could make do this.
Athar (4466)
The important part is the backtrace.
Brian Justice (25)
i saw that in the error when i run it normally and with gdb. wtf does does it mean
Athar (4466)
Tells you in which function and which line the crash happened and which function called that function and where and which function called *that* function and so on.
However, to get meaningful output (i.e. not something like what you posted) you need to compile with -g and link without -s.
Last edited on
ne555 (10692)
Queue::dequeue() always returns invalid pointers.
Brian Justice (25)
Hmm so how would I got about taking a City off of the queue returning it and deleting it? Or is that even possible
ne555 (10692)
You could let the client free the memory.
You could make a two step 
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City *current = queue.front();
// use current
//...
queue.pop(); //returns nothing

You could store and return objects
Last edited on
Brian Justice (25)
Im pretty sure tho my professor only wanted a link list not an array. If thats what your talking about right?
ne555 (10692)
No. ¿What did make you think that?
Brian Justice (25)
Alright here is my new code that ive switched up now dequeue should not have a pointer pointer to nothing when it returns... but i am stil gettting that error


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//Brian Justice
//Assignment 6
// 5/17/12
#include <iostream>
#include <string>
#include <fstream>
#include <cstdlib>
#include <stdio.h>
#include <stdlib.h>
#include <sstream>
using namespace std;

class Queue;
class City;

class Cell {
  friend class Queue;
  Cell *next; City *object;
public:
  Cell (City *o, Cell *n) { next = n; object = o; }
};

class City {
  friend class Queue;
  friend class DataOrganizer;
  Queue *q;       // List of cities this one is directly connected to
  City *from;    // To trace a path back to origin
  string name;    // Name of the city
  bool mark;    // false=unmarked, true=visiting or done

public:
  City ();
  void setName (string theName);
  void neighbor (City *c);
  City *next ();
  void setMark();
  void setFrom(City* g);
  void displayBestRoute ();
  bool checkMark();
  //~City ();
};

//################## Queue class ######################
class Queue {
  friend class City; 
  Cell *tail;
public:
  Queue() { tail = NULL;  }

  void enqueue(City *t) {
    if (t == NULL) return;
    if (tail == NULL) {
      tail = new Cell(t, NULL);
      tail->next = tail;
    }
    else {
      Cell *h = new Cell (t, tail->next);
      tail->next = h;
      tail = h;
    }
  }

  City *dequeue() {
    if (tail == NULL) return NULL;
    Cell *ptr = tail->next;
    City *t = ptr->object;
    if (ptr != tail) tail->next = ptr->next; 
    else tail = NULL;
    delete ptr;
    return t; 
  }
  int isEmpty() { return tail == NULL;  }
}; 

City:: City () { q = new Queue();  from = NULL;  mark = false;  name = ""; }
void City::setName (string theName) { name = theName; }
void City::neighbor (City *c) { q->enqueue(c); }
City *City::next () { return (City *)q->dequeue(); }
void City::setMark() { mark = true; }
void City::setFrom(City* g) { from = g; }
bool City::checkMark() {
  if (mark == true) return true;
  if (mark == false) return false;
}
void City::displayBestRoute () {     // displays route back to city of origin
    cout << name << " ";
    while (from != NULL) {
      cout << from->name << " ";
      from = from;
    }
}
//City::~City() { delete q; if (name != NULL) delete name; }


/////  Organizes Data
class DataOrganizer {
  int count;      // Counts the number of cities
  string name;    // accepts input from the file
  City **cities;

 public:
  DataOrganizer () { count = 0; }

  void readInput (char *filename) {
    fstream *fin = new fstream(filename, ios::in);
    while (true) {
      string buffer;
      *fin >> buffer; 
      if (buffer.compare("-") == 0) break;
      count ++; }
    fin->close();  
    fin->clear();
    
    string tok;
    cities = new City*[count];
    fin->open(filename, ios::in);
    for (int i=0; *fin>>tok && tok != "-"; i++) cities[i]->setName(tok);
    for (int i=0; i < count; i++) {
      for (int j=0; *fin>>tok && tok != "-"; j++) { 
	int n;
	istringstream(tok) >> n;
	cities[i]->neighbor(cities[n]); 
      }  
    }
    fin->close();
    fin->clear();
  }

  City *getOrigin() { return cities[0]; }
  City *getDestination() { return cities[count]; }
};

int main (int argc, char **argv) {
  if (argc != 2) {
    cout << "Usage: " << argv[0] << " \n";
    exit(0);
  }

  DataOrganizer dao;
  dao.readInput(argv[1]);

  // Set origin and destination cities
  City *origin = dao.getOrigin();
  City *destin = dao.getDestination();
  City *city;
  Queue *q = new Queue ();  // Simulate simultaneity

  origin->setMark();
  q->enqueue(origin);
  while (!q->isEmpty()) {
    City *current = (City*) q->dequeue();
    while((city = current->next()) != NULL) {
      if (city == destin) {
	city->setFrom(current);
	cout << "Origin: " << origin << endl;
	cout << "Destin: " << destin << endl;
	city->displayBestRoute();
	return 0;
      }
      if (city->checkMark() != true) {
	city->setMark();
	city->setFrom(current);
	q->enqueue(city);
      }
    }
  }
  cout << "No Route Between Selected Cities\n";
}
ne555 (10692)
¿Do you come from java? To create an object you do Object_type object_name;
I don't understand why you've got so many new (leaking, as there are no matching delete)

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//  void DataOrganizer::readInput (char *filename) {
    cities = new City*[count];
    fin->open(filename, ios::in);
    size_t mark = fin->tellg(); 
    for (int i=0; *fin>>tok && tok != "-"; i++) cities[i]->setName(tok);
You create an array of pointers. Then you dereference those pointers.
You never created any object.

Please use a debugger and perform a backtrace.
Brian Justice (25)
Well i dont know how to use a debugger if you could,could you give a quick run down of gdb, ive tried and got lost. No i dont come from java, my professor gives us most of the code and most of it is from him. Im not sure what you did where would i create an object ? and would it be of City?
ne555 (10692)
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# this is a comment
# If it starts with $ you are in the terminal
# if it starts with > you are in a program waiting for input
#compile with debug information
$ g++ -ggdb file.cpp
#start the debugger
$ gdb
#Load the executable
> file ./a.out
#Execute (with arguments)
> run hops.10.dat
# Now your program will crash (that's good)
# Perform a backtrace to know the function that triggered the error
> backtrace
# A possible output
#0  0x0000000000401255 in City::setName (this=0x7ffff75c5d28, theName=...) at file.cpp:81
#1  0x0000000000401969 in DataOrganizer::readInput (this=0x7fffffffe0b0, filename=0x7fffffffe518 "hops.10.dat") at file.cpp:125
#2  0x00000000004013c6 in main (argc=2, argv=0x7fffffffe1e8) at file.cpp:148
#
# It tells you the function, the line number and the file where the call is located
# In this case main() called readInput() that called setName() that tried name=theName; and crashed
# To see the line you could use your editor, or just inspect the frame
> frame 2
#148             dao.readInput(argv[1]);
# If you want you can see variables
# You need to move to the frame first
# select-frame, up, down
> select-frame 1
> print tok
# this is an structure, so you may to ask for an specific field
# For the content of the string
> print tok._M_dataplus._M_p
You should consult the reference
http://sourceware.org/gdb/current/onlinedocs/gdb/
http://users.ece.utexas.edu/~adnan/gdb-refcard.pdf

Your Queue class is incorrect.
You should focus on fix that first. Make a small unit where you test the functionality.
Check adding and removing elements, print them all, make sure you don't have leaks, etc.
You don't need to use the City class at all here. You better use int as the element for the test.
Brian Justice (25)
Okay so it is running BUT it is not printing out what we want in main, it is in the while loop for a bit and then jumps out? or something straight to ( cout << "No route between selected cities\n"; ) here is are new improved code.

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//Brian Justice
//Assignment 6
// 5/17/12
#include <iostream>
#include <string>
#include <fstream>
#include <cstdlib>
#include <stdio.h>
#include <stdlib.h>
#include <sstream>
using namespace std;

class Queue;
class City;

class Cell {
  friend class Queue;
  Cell *next; City *object;
public:
  Cell (City *o, Cell *n) { next = n; object = o; }
};

class City {
  friend class Queue;
  friend class DataOrganizer;
  Queue *q;       // List of cities this one is directly connected to
  City *from;    // To trace a path back to origin
  string name;    // Name of the city
  bool mark;    // false=unmarked, true=visiting or done

public:
  City ();
  void setName (string theName);
  void neighbor (City *c);
  City *next ();
  void setMark();
  void setFrom(City* g);
  void displayBestRoute ();
  bool checkMark();
  //~City ();
};

//################## Queue class ######################
class Queue {
  friend class City; 
  Cell *tail;
public:
  Queue() { tail = NULL;  }

  void enqueue(City *t) {
    if (t == NULL) return;
    if (tail == NULL) {
      tail = new Cell(t, NULL);
      tail->next = tail;
    }
    else {
      Cell *h = new Cell (t, tail->next);
      tail->next = h;
      tail = h;
    }
  }

  City *dequeue() {
    if (tail == NULL) return NULL;
    Cell *ptr = tail->next;
    City *t = ptr->object;
    if (ptr != tail) tail->next = ptr->next; 
    else tail = NULL;
    delete ptr;
    return t; 
  }
  int isEmpty() { return tail == NULL;  }
}; 

City:: City () { q = new Queue();  from = NULL;  mark = false;  name = ""; }
void City::setName (string name) { name = name; }
void City::neighbor (City *c) { q->enqueue(c); }
City *City::next () { return (City *)q->dequeue(); }
void City::setMark() { mark = true; }
void City::setFrom(City* g) { from = g; }
bool City::checkMark() {
  if (mark == true) return true;
  if (mark == false) return false;
}
void City::displayBestRoute () {     // displays route back to city of origin
    cout << name << " ";
    while (from != NULL) {
      cout << from->name << " ";
      from = from;
    }
}
//City::~City() { delete q; if (name != NULL) delete name; }


/////  Organizes Data
class DataOrganizer {
  int count;      // Counts the number of cities
  string name;    // accepts input from the file
  City **cities;

 public:
  DataOrganizer () { count = 0; }

  void readInput (char *filename) {
    fstream *fin = new fstream(filename, ios::in);
    while (true) {
      string buffer;
      *fin >> buffer; 
      if (buffer == "-") break;
      count ++; }
    fin->close();  
    fin->clear();
     
    string tok;
    int num=0;
    cities = new City*[count];
    fin->open(filename, ios::in);
    while (*fin>>tok) {
      if(tok == "-") break;
      cities[num] = new City;
      cities[num]->setName(tok);
      cout << cities[num]->name;   // not printing out the names.
      num++;
    }
    for (int i=0; i < count; i++) {
      for (int j=0; *fin>>tok && tok != "-"; j++) { 
	int n;
	istringstream buffer(tok);
	buffer >> n;
	cities[i]->neighbor(cities[n]); 
      }
      delete cities[i];  
    }
    fin->close();
    fin->clear();
  }

  City *getOrigin() { return cities[0]; }
  City *getDestination() { return cities[count]; }
};

int main (int argc, char **argv) {
  if (argc != 2) {
    cout << "Usage: " << argv[0] << " \n";
    exit(0);
  }

  DataOrganizer dao;
  dao.readInput(argv[1]);

  // Set origin and destination cities
  City *origin = dao.getOrigin();
  City *destin = dao.getDestination();
  City *city;
  Queue *q = new Queue ();  // Simulate simultaneity

  origin->setMark();
  q->enqueue(origin);
  while (!q->isEmpty()) {
    City *current = (City*) q->dequeue();
    while((city = current->next()) != NULL) {
      if (city == destin) {
	city->setFrom(current);
	cout << "Origin: " << origin << endl;
	cout << "Destin: " << destin << endl;
	city->displayBestRoute();
	return 0;
      }
      if (city->checkMark() != true) {
	city->setMark();
	city->setFrom(current);
	q->enqueue(city);
      }
    }
  }
  cout << "No Route Between Selected Cities\n";
}
ne555 (10692)
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  void readInput (char *filename) { //DataOrganizer
    ifstream fin(filename); //an object, as we only need input we use an input stream
    while (true) { //this will cause trouble if you don't have the "-" word in the input
      string buffer;
      fin >> buffer; 
      if (buffer == "-") break;
      count ++; }
    fin.close(); 
    fin.clear();
     
    string tok;
    int num=0;
    cities = new City*[count];
    fin.open(filename);
    while (fin>>tok) {
      if(tok == "-") break;
      cities[num] = new City;
      cities[num]->setName(tok);
      cout << cities[num]->name;   // ¿why are you printing? Probably a flush issue
      num++;
    }

    for (int i=0; i < count; i++) {
      for (int j=0; fin>>tok && tok != "-"; j++) { 
	int n;
	istringstream buffer(tok);
	buffer >> n;
	cities[i]->neighbor(cities[n]); 
      }
      delete cities[i];  //O_o you are killing all the objects, ¿how do you expect to access them later?, by instance in getOrigin()
    }
    //the destructor will take care
    //fin.close();
    //fin.clear();
  }

int main (int argc, char **argv) {
  if (argc != 2) {
    cout << "Usage: " << argv[0] << " \n";
    exit(0);
  }

  DataOrganizer dao;
  dao.readInput(argv[1]); //let's just test the input
}
Use the debugger and run the program step by step. You will need to set a breakpoint before executing it.
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$ gdb
> file a.out
> breakpoint main
> run hops.10.dat
# Use 'n' for the next line
# Use 's' to 'step into' the function
# Use 'p' to print variables
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