array of pointers to string , segmentation fault occurs - c

Question

I am learning pointer in c
i have written a small program , but i am getting segmentaion fault
i dont know where i am having the issue
please let me know the issue with the code , it is an array of pointers to string ,
which is in a pointer to structure .
# include <stdio.h>
#include <stdlib.h>
# include <string.h>
char *sum(char **sol) ;
char *summer_sum(char*** solcs) ;
int main()
{
char* datum ="teststring";
sum(&datum);
}
char *sum(char** sol)
{
printf("\n value is : %s",*sol);
summer_sum(&sol);
return "1" ;
}
char *summer_sum(char*** solcs)
{
int i=0;
typedef struct
{
char *asg[40];
}nlist;
nlist *n1;
for( i=0 ; i<= 38 ;i++)
{
n1->asg[i] = calloc(1,1*sizeof(*solcs));
strcpy(n1->asg[i],**solcs);
printf("\n %d value is : %s",i,n1->asg[i]);
}
return NULL;
}

Answer 1

n1 is used uninitialized:
n1->asg[i] = calloc(1,1*sizeof(*solcs));
On the other hand, if you want to allocate enough space for the use of strcpy, you must use strlen instead of sizeof
And you don't need a double or triple pointer, your code simplified:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void sum(char *sol);
char *summer_sum(char *solcs);
int main(void)
{
char *datum = "teststring";
sum(datum);
}
void sum(char *sol)
{
printf("\n value is : %s", sol);
summer_sum(sol);
}
char *summer_sum(char *solcs)
{
int i = 0;
size_t len;
typedef struct {
char *asg[40];
} nlist;
nlist *n1 = malloc(sizeof(*n1));
if (n1 == NULL) {
perror("malloc");
exit(EXIT_FAILURE);
}
len = strlen(solcs); /* No need to compute len on each iteration */
for (i = 0; i <= 38; i++) { /* you are filling 39 and declared 40 */
n1->asg[i] = calloc(1, len);
/* Always check the result of (m/c/re)alloc */
if (n1->asg[i] == NULL) {
perror("malloc");
exit(EXIT_FAILURE);
}
strcpy(n1->asg[i], solcs);
printf("\n %d value is : %s", i, n1->asg[i]);
/* Don't forget to free */
free(n1->asg[i]);
}
free(n1);
return NULL;
}

Answer 2

Before using n1->... You will have allocate memory to n1 as well using calloc()

Answer 3

There are two problems which involves dynamic memory allocation in your code:
n1 is not initialized, you should add a statement like n1 = malloc(sizeof(*n1)); before the for statement in summer_sum()
you did not allocate enough space for each asg[i], you should allocate spaces for these asg[i] by n1->asg[i] = malloc(strlen(**solcs) + 1);

Answer 4

You are using your pointer n1 uninitialized. Your program invokes undefined behavior. In such case you may get either expected or unexpected result.
Second, you are missing a closing brace } in function summer_sum.