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Segmentation fault (core dumped)

phuoc557 (2)
please help me figure out the error. thanks

my code is :

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#include <fstream>
#include <iostream>
#include <string>

using namespace std;

struct Leader;
struct Follower;

struct Follower
{
		Leader *adjacentLeader;
		Follower *nextFollower;

};

struct Leader
{
		std::string element;
		int inDegree;
		Leader *nextLeader;
		Follower *firstFollower;
		
};

Leader *head, *tail, *p, *q, *r, *temp;
Follower *f;
string x, y;
int elementCount;

void TopologicalSort(ifstream&);
Leader *BuildList(string,Leader*&,Leader*&,int);
void PrintIn();

int main()
{
	ifstream inFile;
	TopologicalSort(inFile);
	return 0;
}

void TopologicalSort(ifstream &inFile)
{
	
	inFile.open("CS_Prerequisites.txt");
		if(!inFile.is_open())
		{
			cout<<"error finding file"<<endl;
			return;

		}
		
	head = new Leader;
	tail = head;
	elementCount =0;
	getline(inFile,x);
		while(!inFile.eof())
		{
			getline(inFile,y);
			p = BuildList(x,head,tail,elementCount);
			q = BuildList(y,head,tail,elementCount);
			f = new Follower;
			f -> adjacentLeader=q;
			f -> nextFollower = p -> firstFollower;
			p-> firstFollower = f;
			q -> inDegree++;
			getline(inFile,x);
					
		}
	
	PrintIn();
	p = head;
	head = NULL;
	r = tail;
	
	
	int i = 0;
		while(p != r)
		{
			q = p;
			p = p ->nextLeader;
			if(q -> inDegree == 0)
			{
				q -> nextLeader = head;
				head = q;
				i++;
				if(i==1)
					tail = q;
			}
			
		}
	q = head;
	r = tail;
		while( q != NULL)
		{
			cout << q ->element;
			elementCount --;
			f= q -> firstFollower;
			q = q -> nextLeader;
			while( f !=NULL)
			{
				p = f -> adjacentLeader;
				p-> inDegree --;
				if(p -> inDegree == 0)
				{
					p-> nextLeader = NULL;
					r-> nextLeader = p;
					r=p;
					if (q == NULL)
						q=r;
					
				}
				f = f ->nextFollower;
			}
			
		}
		if (elementCount !=0 )
			cout << "ERROR - SET NOT PARTIALLY ORDERED"<<endl;
}

Leader* BuildList ( string w, Leader* &head, Leader* &tail, int i)
{
	Leader *h = head;
	tail -> element = w;
	while(h -> element !=w)
		h = h -> nextLeader;
	if ( h == tail)
	{
		tail = new Leader;
		i++;
		h -> inDegree=0;
		h -> firstFollower = NULL;
		h -> nextLeader = tail;
		
	}
	return h;
}

void PrintIn()
{
	
	temp = head;
	int j = 0;
	temp ++;
	while(temp != tail)
	{
		j++;
		cout << "Leader "<<j<<endl;
		cout<<"Element = "<< temp ->element << endl;
		cout<< "inDegree = "<< temp->inDegree<<endl;
		if ( temp ->firstFollower == NULL)
		{
			cout << "Follower 1 = N/A"<<endl;
		}
		else
		{
			cout << "Follower 1 = "<<temp->firstFollower ->adjacentLeader->element<< endl;
			if( temp -> firstFollower->nextFollower == NULL)
				cout << "Follower 2 = N/A"<< endl;
			else
				cout << "Follower 2 = "<< temp->nextLeader->element;
			
		}
	}
	
	temp ++;
	
	
}
Last edited on
darshantm (2)
HI,

there are no error in this program
as u need to place the txt file which u r trying to open it.

if u facing any error please do mention the error mess

Cheers..!!
TheIdeasMan (6782)
Hi,

Have you tried using a debugger? You can step through the code line by line, keeping an eye on the variables with a watch list and deduce where things go wrong. You can also set break points.

If you are using an IDE, hopefully there will be a GUI debugger built in. If not, there are command line versions like gdb.

If you learn how to do this, then it will save you days of messing around :+)

Hope all goes well, cheers
kbw (9488)
You're just asking for trouble, writing code like that. C++ was designed to avoid the sort of problems you're having. Even if you fix the particular problem you're having, you can never be sure that the program is error free.

The problems are:
1. Global variables
2. All those pointers
3. No local scopes
4. Lots of unclear code

For example:
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void PrintIn()
{
	temp = head;
	int j = 0;
	temp ++;		// What does this mean?

phuoc557 (2)
I debug it and it give me this, can someone help me please?


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Program received signal SIGSEGV, Segmentation fault.
std::operator<< <char, std::char_traits<char>, std::allocator<char> > (__os=..., __str=<value optimized out>)
    at /usr/src/debug/gcc-4.4.7-20120601/obj-x86_64-redhat-linux/x86_64-redhat-linux/libstdc++-v3/include/bits/basic_string.h:2503
2503          return __ostream_insert(__os, __str.data(), __str.size());
(gdb) ^C(gdb) Quit
(gdb) ^C(gdb) Quit
(gdb) bt
#0  std::operator<< <char, std::char_traits<char>, std::allocator<char> > (__os=..., __str=<value optimized out>)
    at /usr/src/debug/gcc-4.4.7-20120601/obj-x86_64-redhat-linux/x86_64-redhat-linux/libstdc++-v3/include/bits/basic_string.h:2503
#1  0x0000000000401529 in PrintIn () at new1.cpp:149
#2  0x00000000004011bb in TopologicalSort (inFile=...) at new1.cpp:71
#3  0x0000000000400f40 in main () at new1.cpp:38
coder777 (8439)
As kbw pointed out: Line 144 makes the pointer invalid and it crashes on line 149 because of that.
#1 0x0000000000401529 in PrintIn () at new1.cpp:149
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