Thread: Return of the multiplication function

Hello, I'm beginner in C, use kdevelop -> Qt: 3.3.6 KDE: 3.5.4-Red Hat 25.el5.centos.1 KDevelop: 3.3.4
and the compiler is gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)

My doubt is that I made a function (mult_mat_vet) to multiply a matrix (9x9) and a vector (9) and I couldn't return the resulting vector multiplication, within the function I can visualize the result of multiplying, but when the program exits the function tells me that great message: "segmentation fault", I need the y vector to make other important things, sending down the algorithm, summarized, and look forward to your help. Thanks in advance.

Code:

#include<stdio.h>
#include<math.h>
#include<stdlib.h>

float *allocate_vector (int n)
{
	float *v; 
	if (n<1) {
	printf("ERROR INVALID PARAMETER!!!");
	return (NULL);
	}
	v=(float *)malloc(n*sizeof(float));
	if (v==NULL){
	printf("ERROR - NO MEMORY");
	return(NULL);
	}
	else //printf("\nOK!!!\n");
	return (v);
}

float **allocate_matrix(int m,int n)
{
	float **v; 
	int i;	
	if(m<1||n<1)
	{	
		printf("\nINVALID PARAMETER\n");
		return(NULL);
	}
	//aloca as linhas da matriz
	v=(float **)calloc(m,sizeof(float *));
	if(v==NULL)
	{
		printf("ERROR - NO MEMORY!!");
		return(NULL);
	}
	for (i=0;i<m;i++)
	{
		v[i]=(float *)calloc(n,sizeof(float)); 
		if (v[i]=NULL)
		{
			printf("ERROR - NO MEMORY!!");
			return(NULL);
		}
	}
	return(v); 
}

float **read_matrix(int *nlin, int *ncol) {
  FILE  *fr;
  float **matriz;
  int i, j;

  fr = fopen ("ridge.txt", "r");

  if (fr == NULL) {
    perror("ridge.txt: ");
    exit(-1);  
  }
  
  matriz = (float **) calloc (*nlin, sizeof(float*));
  
  for (i = 0; i < *nlin; i++)
    matriz[i] = (float *) calloc(*ncol, sizeof(float));

  for (i = 0; i < *nlin; i++)
    for (j = 0; j < *ncol; j++)
    fscanf(fr, "%f", &matriz[i][j]);

  fclose(fr);


  return matriz;

}


float *mult_mat_vet(int lin,int col,int linvet, float **mat,float *vetin)
{
	int i,j,k;
	float *vetout;
	vetout=allocate_vector(9);
	for(i=0;i<lin;i++)
	{
		for(j=0;j<col;j++)
			vetout[i]=vetout[i]+mat[i][j]*vetin[j];
	printf("\nvector %f",vetout[i]); //JUST TO TEST THE MULTIPLICATION!!
	}
	return(vetout) ;
}


main()
{
	
	float *y,**A;
	int nlin,ncol;
	/*SYNTHECT VECTOR*/
	float Ap[9]={1,0.7,0.2,0.62,1.2,0.9,1,1.08,1.2};
	
	nlin=9;
	ncol=9;

      A = read_matrix(&nlin, &ncol);

	p=Ap;
	
	y=mult_mat_vet(9,9,9,A,p);
	printf("\n Don't get here!!!!!!!!!");

//...
//..
//. 
//should continue with others commands
return
}

After you allocate memory for vetout, its elements are some unpredictable values. Summing into them is dangerous. The results could be anything. This wouldn't normally account for segmentation faults though. So let's fix one problem at a time.

When I printed the vector vetout I could see it.

So what should I do?

Hmmm, then I have to compile this myself. I will try if I don't get distracted with work.

Please, help me if you can.

Funny, my compiled code runs perfectly. I don't understand it.

However in your function allocate_matrix(), which is not called in your example, you have

Code:

if (v[i]=NULL)

. You meant to use '=='. Otherwise, you're assigning NULLs and wrecking your allocated pointers.

The code already complies before but gave problems when running, but now WORKED !!!!!

I changed two things:
when I was allocating the matrix was

Code:

if (v[i]=NULL)

and now is:

Code:

if (v[i]==NULL)

And the other thing was not pass nlin and ncol as pointers and only as integers, these two things have changed and now the code is ok, someone explains to me why?

Grateful

Since you never called allocate_matrix() in the program you posted, fixing the v[i]=NULL problem shouldn't have mattered. I also don't see where you passed nlin and ncol erroneously. You must be working from another version of the code.