Reading a Structure using pointer second time gives segmentation fault error - c

Question

When I read the second vector using vector_read() function or by intializing it to zero by usign vector_init_zero() I get segementation fault. I have searched it alot still not got the answer why it's happening. If I use only one pointer and don't initiallize it to 0 it works fine. Every other function works fine with single variable of structure pointer.
#include <stdio.h>
#include <stdlib.h>
typedef struct vector_s
{
int dim;
float *data_ptr;
} vector_type;
/* Allocate and initialize to 0 a vector with the given dimension */
void vector_init_zeros(vector_type *v_ptr, int dim)
{
v_ptr->dim = dim;
v_ptr->data_ptr = (float *)calloc(dim, sizeof(float));
#ifdef DEBUG
if (v_ptr->data_ptr == 0)
{
printf("vector_init_zeros error: calloc returned a null ptr\n");
exit(1);
}
#endif
}
/* Free up a vector that was allocated using vector_init_zeros */
void vector_deinit(vector_type *v_ptr)
{
v_ptr->dim = 0;
free(v_ptr->data_ptr);
v_ptr->data_ptr = 0;
}
/* Attempt to read a vector from stdin. */
/* Returns 1 if read successful and 0 otherwise */
int vector_read(vector_type *v_ptr)
{
int i;
float next;
for (i = 0; i < v_ptr->dim; i++)
{
if (scanf("%g\n", &next) != 1)
{
return 0;
}
v_ptr->data_ptr[i] = next;
}
return 1;
}
/* w = u + v */
void vector_add(vector_type *u_ptr, vector_type *v_ptr,
vector_type *w_ptr)
{
int i;
for (i = 0; i < v_ptr->dim; i++)
{
w_ptr->data_ptr[i] = u_ptr->data_ptr[i] + v_ptr->data_ptr[i];
}
}
/* v = cv */
void vector_scalar_mult(vector_type *v_ptr, float c)
{
int i;
for (i = 0; i < v_ptr->dim; i++)
{
v_ptr->data_ptr[i] = v_ptr->data_ptr[i] * c;
}
}
/* print the compondents of the given vector */
void vector_print(vector_type *v_ptr)
{
int i;
for (i = 0; i < v_ptr->dim; i++)
{
printf("%f ", v_ptr->data_ptr[i]);
}
printf("\n");
}
int main()
{
int dim;
int count = 0;
if (scanf("%d", &dim) != 1)
{
printf("Error reading the vector dimension from stdin\n");
exit(1);
}
vector_type *s,*t;
vector_init_zeros(s, dim);
vector_init_zeros(t, dim);
vector_read(s);
vector_read(t);
}

Answer 1

In main() where you declare s and t, you never initialize them. You can either declare them as structure variables and pass their addresses to the functions with the & 'address of' operator or allocate and deallocate them with malloc() and free() or equivalents.
int main(){
...
vector_type s, t;
...
vector_init_zeros(&s, dim);
vector_init_zeros(&t, dim);
vector_read(&s);
vector_read(&t);
}
or
int main(){
...
vector_type *s, *t;
s = (vector_type *) malloc(sizeof(vector_type));
t = (vector_type *) malloc(sizeof(vector_type));
...
free(s);
free(t);
}