How to get whole structure from function? - c

Question

This is my code:
#include <stdio.h>
typedef struct
{
char name[100];
char number[100];
} contact_t;
void empty_array(char *line)
{
for (int j = 0; line[j] != '\0'; j++)
{
line[j] = '\0';
}
}
void read_text(contact_t *contact)
{
int c, cnt = 0;
int i = 0;
char line[100];
do
{
c = getchar();
if ( (c == '\n') || (c == EOF))
{
if( cnt % 2 == 0)
{
for(int j = 0; line[j] != '\0'; j++)
contact -> name[j] = line[j];
}
else
{
for(int j = 0; line[j] != '\0'; j++)
contact -> number[j] = line[j];
}
empty_array(line);
i = 0;
cnt++;
}
line [i] = c;
i++;
} while (c != EOF);
}
int main()
{
contact_t contact = {"x", "0"};
int *j_ptr;
read_text(&contact);
printf("%s", contact.name);
printf("%s", contact.number);
return 0;
}
I am reading a text file(6 lines, name and number, name and number...) from standard input. Then I assign every second line(starting from the first) from that text file to structure contact.name and the rest are I assign to contact.number. So I have several 3 contact structures. I managed to pass to main only the last one, because I don't know how to get acces to int cnt and again make a for cycle.
This is what last prints give me:
John Green
254454556
UPDATE:
I am sorry for not being clear enough as I was writing this question in a hurry. This code is a part of school project and we are not allowed to work with dynamically allocated memory or use fscanf, fopen, qsort, lsearch, bsearch and hsearch etc. Basically, I would just like to use pointers to index of array line and then in main function use a for cycle again to pass all structures from the function read_text to main function of the program.

Answer 1

A few issues ...
main only provides space for one contact entry
read_text needs to use a dynamic array (vs. overwriting the same entry)
read_text needs to return the list pointer and the count to the caller (e.g. main)
The method used in read_text is a bit convoluted.
Style fixes:
contact -> name --> contact->name
list [i] --> list[i]
Here is the refactored code. It is annotated:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct {
char name[100];
char number[100];
} contact_t;
int
read_text(contact_t **listp)
{
char buf[1000];
contact_t *list = NULL;
char *cp = NULL;
int cnt = 0;
// loop on input until EOF
while (fgets(buf,sizeof(buf),stdin) != NULL) {
// increase size of list
++cnt;
list = realloc(list,sizeof(*list) * cnt);
// handle error
if (list == NULL) {
perror("realloc/increase");
exit(1);
}
// point to current record
contact_t *contact = &list[cnt - 1];
// get first name
contact->name[0] = 0;
cp = strtok(buf," \n");
if (cp == NULL)
break;
strcat(contact->name,cp);
// add separater
strcat(contact->name," ");
// get last name
cp = strtok(NULL," \n");
if (cp == NULL)
break;
strcat(contact->name,cp);
// get number
cp = strtok(NULL," \n");
if (cp == NULL)
break;
strcpy(contact->number,cp);
}
// trim to actual amount stored (if error)
if ((cp == NULL) && (cnt > 0)) {
--cnt;
list = realloc(list,sizeof(*list) * cnt);
if (list == NULL) {
perror("realloc/trim");
exit(1);
}
}
// give caller the list pointer
*listp = list;
return cnt;
}
int
main(void)
{
int cnt;
contact_t *list;
cnt = read_text(&list);
// print all entries read in
for (int idx = 0; idx < cnt; ++idx) {
contact_t *contact = &list[idx];
printf("'%s' '%s'\n",contact->name,contact->number);
}
return 0;
}
Here is the test input I used:
John Green 254454556
Fred Smith 8765309
Bob Jones 99728967341
Mary Gallagher 4329268757
Here is the program output:
'John Green' '254454556'
'Fred Smith' '8765309'
'Bob Jones' '99728967341'
'Mary Gallagher' '4329268757'
UPDATE:
I am sorry, I should have clarified that I cannot use dynamically allocated memory. Malloc, calloc or also fsangf is not available –
gregalz
Okay, no malloc et. al. Ironically, I was going to use a predefined fixed size array. But, decided to use a dynamic array instead ;-)
Not sure what fsangf is. So, I'll assume that's fscanf. If you're heavily restricted, maybe you should edit your question and post what you can and can not use.
Here's the code that uses just a fixed array:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct {
char name[100];
char number[100];
} contact_t;
#define NLIST 1000
contact_t list[NLIST];
int
read_text(contact_t *list,int max)
{
char buf[1000];
char *cp = NULL;
int cnt = 0;
// loop on input until EOF
while (fgets(buf,sizeof(buf),stdin) != NULL) {
// don't overflow the max size
if (cnt >= max)
break;
// point to current record and increase list count
contact_t *contact = &list[cnt++];
// get first name
contact->name[0] = 0;
cp = strtok(buf," \n");
if (cp == NULL)
break;
strcat(contact->name,cp);
// add separater
strcat(contact->name," ");
// get last name
cp = strtok(NULL," \n");
if (cp == NULL)
break;
strcat(contact->name,cp);
// get number
cp = strtok(NULL," \n");
if (cp == NULL)
break;
strcpy(contact->number,cp);
}
// trim to actual amount stored (if error)
if ((cp == NULL) && (cnt > 0))
--cnt;
return cnt;
}
int
main(void)
{
int cnt;
cnt = read_text(list,NLIST);
// print all entries read in
for (int idx = 0; idx < cnt; ++idx) {
contact_t *contact = &list[idx];
printf("'%s' '%s'\n",contact->name,contact->number);
}
return 0;
}