CODEWITHSUNDEEP
cdynamicmalloc
Mel
Mel

Reputation: 175

Memory allocation for a matrix

I have written code that generates a matrix with NODES rows and each row has a user specified number of columns (see node_degree below). I then fill each entry in the matrix with some value (the value doesn't matter).

When I build the program on Fedora using Geany, I receive no error messages. However, when I run the program I get:

./geany run script.sh line 5: 3586 Segmentation fault (core dumped)"./ ad_matrix_outside_main

Note: ad_matrix_outside_main is the name of the c file.

Here is the program: 

#include <stdio.h>
#include <stdlib.h>
#define NODES (10)
#define CONNECTED (5)

int main()
{
int i, j;
double **matrix;

matrix = (double **)malloc(sizeof(double *)*NODES); 

int node_degree[CONNECTED]; //Example: 5 nodes are connected (have non-zero degree).    

for(i=0; i<CONNECTED; i++)
{
    printf("Enter degree of node %d\n", i);  //Index is node, value is degree. 
    scanf("%d", &node_degree[i]);                               
} 

for(i=0; i<CONNECTED; i++)
{
    matrix[i] = (double*)malloc( sizeof(double)* (node_degree[i] + 1) );
}

for(i=0; i<NODES; i++) 
{

    for(j=0; j<node_degree[i]; j++) 
    {
        matrix[i][j] = j; //j can be the node that node i connected to. 
    }
    matrix[i][j] = NODES; 
}

for(i=0; i<NODES; i++)
{
    free( matrix[i] );
}

free(matrix);
return(0);
}

What could be causing the error? I have a feeling my notation might be the problem.

Upvotes: 2

Views: 107

Answers (1)

Varvarigos Emmanouil
Varvarigos Emmanouil

Reputation: 757

#include <stdio.h>
#include <stdlib.h>
#define NODES (10)
#define CONNECTED (5)

int main()
{
int i, j;
double **matrix;

matrix = (double **)malloc(sizeof(double *)*NODES); 

int node_degree[CONNECTED]; //Example: 5 nodes are connected (have non-zero degree).    

for(i=0; i<CONNECTED; i++)
{
    printf("Enter degree of node %d\n", i);  //Index is node, value is degree. 
    scanf("%d", &node_degree[i]);                               
} 

for(i=0; i<CONNECTED; i++)
{
    matrix[i] = (double*)malloc( sizeof(double)* (node_degree[i] + 1) );

//here you malloc for 5 }

for(i=0; i<NODES; i++) 
{

    for(j=0; j<node_degree[i]; j++) 
    {
        matrix[i][j] = j; //j can be the node that node i connected to. 
    }
    matrix[i][j] = NODES;

//here you assign for 10! }

for(i=0; i<NODES; i++)
{
    free( matrix[i] );
}

free(matrix);
return(0);
}

Upvotes: 1

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