Question

I have a process that get killed immediately after executing the program. This is the code of the compiled executable, and it is a small program that reads several graphs represented by numbers from standard input (a descriptive file usually) and finds the minimum spanning tree for every graph using the Prim’s algorithm (it does not show the results yet, it just find the solution).

#include <stdlib.h>  
#include <iostream>  

using namespace std;

const int MAX_NODOS = 20000;
const int infinito = 10000;

int nnodos;
int nAristas;
int G[MAX_NODOS][MAX_NODOS]; 
int solucion[MAX_NODOS][MAX_NODOS];
int menorCoste[MAX_NODOS];
int masCercano[MAX_NODOS];



void leeGrafo(){
    if (nnodos<0 || nnodos>MAX_NODOS) {
        cerr << "Numero de nodos (" << nnodos << ") no valido\n";
        exit(0);
    }  
    for (int i=0; i<nnodos ; i++)
        for (int j=0; j<nnodos ; j++)
            G[i][j] = infinito; 
    int A,B,P;
    for(int i=0;i<nAristas;i++){
        cin >> A >> B >> P; 
        G[A][B] = P;
        G[B][A] = P;
    }   
}


void prepararEstructuras(){
    // Grafo de salida
    for(int i=0;i<nnodos;i++)
        for(int j=0;j<nnodos;j++)
            solucion[i][j] = infinito;
    // el mas cercaano 
    for(int i=1;i<nnodos;i++){
        masCercano[i]=0;
        // menor coste
        menorCoste[i]=G[0][i];
    }           
}

void prim(){
    prepararEstructuras();
    int min,k;  
    for(int i=1;i<nnodos;i++){
        min = menorCoste[1];
        k = 1;
        for(int j=2;i<nnodos;j++){
            if(menorCoste[j] < min){
                min = menorCoste[j];
                k = j;
            }
        }
        solucion[k][masCercano[k]] = G[k][masCercano[k]];
        menorCoste[k] = infinito;
        for(int j=1;j<nnodos;j++){
            if(G[k][j] < menorCoste[j] && menorCoste[j]!=infinito){
                menorCoste[j] = G[k][j];
                masCercano[j] = k;
            }       
        }           
    }
}

void output(){
    for(int i=0;i<nnodos;i++){
        for(int j=0;j<nnodos;j++)
            cout << G[i][j] << ' ';
        cout << endl;
    }
}

int main (){
    while(true){
        cin >> nnodos;
        cin >> nAristas;
        if((nnodos==0)&&(nAristas==0)) break;
        else{
            leeGrafo();
            output();
            prim(); 
        }
    }   
}

I have learned that i must use strace to find what is going on, and this is what i get :

execve("./412", ["./412"], [/* 38 vars */] <unfinished ...>
+++ killed by SIGKILL +++
Killed

I am runing ubuntu and this is the first time i get this type of errors. The program is supposed to stop after reading two zeros in a row from the input wich i can guarantee that i have in my graphs descriptive file. Also the problem happens even if i execute the program without doing an input redirection to my graphs file.

Answer 1

Although I’m not 100% sure that this is the problem, take a look at the sizes of your global arrays:

const int MAX_NODOS = 20000;

int G[MAX_NODOS][MAX_NODOS]; 
int solucion[MAX_NODOS][MAX_NODOS];

Assuming int is 4 bytes, you’ll need:

20000 * 20000 * 4 bytes * 2 = ~3.2 GB

For one, you might not even have that much memory. Secondly, if you’re on 32-bit, it’s likely that the OS will not allow a single process to have that much memory at all.

Assuming you’re on 64-bit (and assuming you have enough memory), the solution would be to allocate it all at run-time.