Segmentation Fault

This is a discussion on Segmentation Fault within the C Programming forums, part of the General Programming Boards category; I tried another version of my program(post "memory problem") with lists.But now i´m having a segmentation fault problem. here´s the ...

  1. #1
    Registered User Lost__Soul's Avatar
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    Segmentation Fault

    I tried another version of my program(post "memory problem") with lists.But now i´m having a segmentation fault problem.
    here´s the code:
    Code:
    #include <stdio.h>
    #define MAX 1000  /* Array limit */
    
    int percurso[MAX]; /* must be dinamic */
    int cara=0,coroa=0;
    int maxpeso=-1000000000; /* another infinite */
    int in;
    int ja_ta=0;
    int somei=0;
    
    typedef struct as_adjacencias
    {
    	int vertice;
    	int peso;
    	struct as_adjacencias *proximo;
    } ADJACENCIAS;
    
    typedef ADJACENCIAS* adjacencias;
    
    void insere (adjacencias* Adjacencias, int nof, int peso)
    {
    	if(*Adjacencias == NULL)
    		{
    			*Adjacencias=(adjacencias)malloc(sizeof(ADJACENCIAS));
    			if(*Adjacencias == NULL)
    				return;
    				(*Adjacencias) -> vertice=nof;
    				(*Adjacencias) -> peso=peso;
    				(**Adjacencias).proximo = NULL;
    		}
    		else
    			insere (&(**Adjacencias).proximo, nof, peso);
    }
    adjacencias proximo_elemento (int elemento, adjacencias* Adjacencias)
    {
         if (elemento == (*Adjacencias) -> vertice)
              return (**Adjacencias).proximo;
    
         return proximo_elemento (elemento, &(**Adjacencias).proximo);
    }
    
    adjacencias lista[7001]; /*must be dinamic */
    
    void poe_na_fila(int x) 
    {
    	percurso[coroa]=x;
    	coroa++;
    }
    int peso_elemento(adjacencias *Adjacencias, int b)
    {
         if (b== (*Adjacencias) -> vertice)
              return (*Adjacencias) -> peso;
    
         return peso_elemento (&(**Adjacencias).proximo,b);
    }
    
    
    int somador(int percurso[],int nos)
    {
    	int i=0,soma=0;
    	somei=1;
    	for(i=0; i< coroa-1;i++)
    		soma += peso_elemento(&lista[percurso[i]],percurso[i+1]);
    	return soma;
    }
    		
    void max_peso(int source, int sink, int nodes, adjacencias proximo)
    {
        int u = 0, n = 0;
        if ( ja_ta ) return;
        if (proximo==NULL && source == in) 
        {
            ja_ta = 1;
            return;
        }
        else
        {
            if (source == sink) {
                poe_na_fila(source);
            }
            else
            {
                if (proximo==NULL)
                {
                    percurso[coroa] = 0;
                    coroa -= 1;
                    max_peso(percurso[coroa], sink, nodes,proximo_elemento(source, &(*(lista+percurso[coroa]))));
                }
                else
                {
                    	
                        poe_na_fila(source);
                        max_peso(proximo->vertice, sink, nodes, lista[proximo->vertice]);
                    
                }
            }
            if ( ja_ta ) return;
            else
            {
            n = somador(percurso, nodes);
            if (n > maxpeso)
                maxpeso = n;
            coroa = coroa - 1;
            percurso[coroa] = 0;
            coroa = coroa - 1;
             max_peso(percurso[coroa], sink, nodes, proximo_elemento(source, &(*(lista+percurso[coroa]))));
            }
        }
    }
    
    main (int argc, char *argv[])
    {
    	int noi,nof,peso,i,u,j,arcos,nos,inicio,fim;
    	inicio=fim=noi=nof=i=j=peso=arcos=nos=u=0;
    	FILE *fp;
    	fp=fopen(argv[1],"r");
    	if (fp==NULL)
    		printf("Impossível abrir o ficheiro %s", argv[1]);
    	else
    		{
    			fscanf(fp,"%d",&nos);
    			fscanf(fp,"%d",&arcos);
    			for(u=0;u<=nos;u++)
    			{
    				percurso[u]=0;
    			}
    			for(j=0; j<=nos;j++)
    				lista[j]=NULL;
    			for(i=0;i<arcos;i++)
    			{
    				
    				fscanf(fp,"%d %d %d", &noi,&nof,&peso);
    				insere(&lista[noi],nof,peso);
    			}
    			fscanf(fp,"%d %d", &inicio, &fim);
    			in=inicio;
    			max_peso(inicio,fim,nos,lista[inicio]);
    			if(somei)
    			printf("%d\n",maxpeso);
    			else
    			printf("NA\n");
    		}
    		
    
    }
    As I said in previous posts,the idea is to calculate max flow along a directed graph.The path is stored in the array percurso.For example:
    7
    9
    1 2 1
    2 3 2
    3 4 3
    4 5 4
    5 6 5
    6 7 6
    1 3 4
    3 5 8
    5 7 12
    1 7
    the first path stored is 1-2-3-4-5-6-7(since we want to compute the max flow between nodes 1 and 7).Then there´s somador that calculates the flow,which is correct,21.Then the program start "moving backwards",trying to look for other paths. To do that,i have to look at the next element of the adjency list of each node. For example 6 only has a transition to 7,so proximo will be NULL. This works fine until it gets to five.Since it already used the 6 transition, it discovers the 7 one, the path becomes 1-2-3-4-5-7,but the calculated flow results in 14,and not 22,as it should be.This is my first problem.
    The second is when it begins moving backwards again. Its going to search for alternative paths in 5,which sould be NULL,since there arent any others,but its not,and i get segmentation fault...
    Can anyone help me?this is probably one of those small errors so hard to find...
    Last edited by Lost__Soul; 04-20-2003 at 11:32 AM.

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    I just ran you code using the test data with no segmentation fault.

    maxpeso = 24 when completed.

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    Registered User Lost__Soul's Avatar
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    Holly $$$$,thats the correct result!How do i get this segmentation fault problem?

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    When I complile your code I get the following warnings which could cause a problem, as it could return a random value!, which could be the correct value when run on my PC but not yours?

    warning C4715: 'proximo_elemento' : not all control paths return a value
    Code:
    adjacencias proximo_elemento (int elemento, adjacencias* Adjacencias)
    {
    	if (elemento == (*Adjacencias) -> vertice)
    	return (**Adjacencias).proximo;
    	else proximo_elemento (elemento, &(**Adjacencias).proximo);
    }
    warning C4715: 'peso_elemento' : not all control paths return a value
    Code:
    int peso_elemento(adjacencias *Adjacencias, int b)
    {
    	if (b== (*Adjacencias) -> vertice)
    		return (*Adjacencias) -> peso;
    	else peso_elemento (&(**Adjacencias).proximo,b);
    }

  5. #5
    Registered User Lost__Soul's Avatar
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    I´m compiling in eclipse,which is the program i´m obligated to use...I get a segmentation fault in the program run and when i run the debug i realize that some flows arent correctly computed,but the result in your pc is correct,and thats the result of the last flow,so the others are correct as well...Is there any C++ or "not so ANSI C" stuff in my code?cant understant this!

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    Try adding returns shown in the following functions that I described in my last post. With this change I still get 24.
    Code:
    adjacencias proximo_elemento (int elemento, adjacencias* Adjacencias)
    {
         if (elemento == (*Adjacencias) -> vertice)
              return (**Adjacencias).proximo;
    
         return proximo_elemento (elemento, &(**Adjacencias).proximo);
    }
    
    int peso_elemento(adjacencias *Adjacencias, int b)
    {
         if (b== (*Adjacencias) -> vertice)
              return (*Adjacencias) -> peso;
    
         return peso_elemento (&(**Adjacencias).proximo,b);
    }
    I'm compiling with MS Visual Studio C++ v6
    Last edited by Scarlet7; 04-20-2003 at 06:24 AM.

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    Or, it could be that the stack size on your comple is to small for the level of recursion. The MS VC6 that I'm using may default to a higher stack size than yours. Try increasing the stack size.
    Last edited by Scarlet7; 04-20-2003 at 06:44 AM.

  8. #8
    Registered User Lost__Soul's Avatar
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    Ok,now its working fine but only with small inputs.For example:
    http://mega.ist.utl.pt/~smcos/t4.in
    or:
    http://mega.ist.utl.pt/~smcos/t5.in

    I get errors.In t4,i dont get a result at all,and in t5 i get segmentation fault.And believe me,these are the small inputs...My program must work with a 16 mb one.Maybe its that stack thing,how do i increase it?

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    It depends on your compiler/linker. In VC6 I add a link option /stack: If for example, setting the stack to 15 mb I use the following link option:

    /stack:0xe4e1c0

    Which may be different on your compiler.
    Last edited by Scarlet7; 04-20-2003 at 07:28 AM.

  10. #10
    Registered User Lost__Soul's Avatar
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    I´m using eclipse,cywin and gcc...But where do i write that?in the code?Can u help me make my program work with those large files?im quite a begginner...

  11. #11
    Registered User Lost__Soul's Avatar
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    So,do i have to work with the stack?there must be some way of making the program capable of handling those big files.What sould i do?Any ideas?

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    I'm not sure if the stack size is the root of the problem (too sleepy to read it thru yet... might do it tomorrow

    Anyway, there is a "limit" command which you can use to increase the OS stack size on Unix like machine:

    limit stack 32M

  13. #13
    Registered User Lost__Soul's Avatar
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    Thnks,hope u can help me.The other thing i must do is turn the percurso array into a dinamic one .It must have the number of nodes(nos).For that i only have to do something like percurso=(int)malloc(sizeof(int)*nos), right? I can post the 16 mb file in my home page to see if anyone can help me making my program work with that kind of file.For now,i have the 500 kb ones to handle.

  14. #14
    Registered User Lost__Soul's Avatar
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    Like u said,there are no low limits so we must work in another solution.The only thing i know is that my program will be tested with very big files,so i have to prepare it for that.

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    Just tried running using t5.in and I'm getting a stack overflow.

    I set the stack to 40 mb and still getting stack overflow. I added a counter to count the levels of recursion which gets to 345085 levels before overflow which is not suprising.

    I set then set the stack to 100 mb and overflowed at recursion level 862026.

    200mb stack = recursion level 1724166 before overflow. This will never work until the recursion problem is sorted out.
    Last edited by Scarlet7; 04-20-2003 at 11:02 AM.

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