nested structures with pointer in C - c

Question

i want to use nested structures with pointers in c. i write this code but i dont know why this code not working. actually how can i allocate memory for my second structure?
#include <stdio.h>
#include <stdlib.h>
struct address
{
int code;
char city[10];
};
struct student {
char name[10];
struct address *ads;
} *person1;
int main()
{
person1 = malloc(sizeof(struct student));
scanf("%s", person1->name);
scanf("%d", &person1->ads->code);
scanf("%s", person1->ads->city);
printf("%s", person1->name);
printf("%d", person1->ads->code);
printf("%s", person1->ads->city);
return 0;
}
NOTE: when i use "person1->ads = malloc(sizeof(struct address));" program ran to problem and stop working.
[Update from comment:]
I use DEV C++ v5.4.2

Answer 1

You need to also allocate memory for members stored via pointer.
int main()
{
person1 = malloc(sizeof(struct student));
person1->ads = malloc(sizeof(struct address));
scanf("%s", person1->name);
scanf("%d", &person1->ads->code);
scanf("%s", person1->ads->city);
printf("%s", person1->name);
printf("%d", person1->ads->code);
printf("%s", person1->ads->city);
free(person1->ads);
free(person1);
return 0;
}

Answer 2

You have a few poblems
You don't check the success of malloc.
You don't malloc for person1->ads member.
You don't check the success of scanf.
This is a fixed and anotated version of your code
#include <stdio.h>
#include <stdlib.h>
struct address
{
int code;
char city[10];
};
struct student
{
char name[10];
struct address *ads;
};
int main()
{
/* You don't need te struct to be global, and it's generally a bad idea, not always of course */
struct student *person;
/* you should check that malloc succeeded otherwise undefined behavior would happen */
person = malloc(sizeof(*person));
if (person == NULL)
{
printf("cannot allocate memory\n");
return -1;
}
/* you should check that scanf succeeded too */
if (scanf("%9s", person->name) != 1)
/* ^ prevent buffer overflow */
{
printf("Invalid, input\n");
free(person);
return -1;
}
person->ads = malloc(sizeof(*(person->ads)));
if (person->ads == NULL)
{
printf("cannot allocate memory\n");
/* on failure free successfuly allocated person */
free(person);
return -1;
}
/* you should check that scanf succeeded too */
if (scanf("%d", &person->ads->code) != 1)
{
printf("Invalid, input\n");
free(person->ads);
free(person);
return -1;
}
/* you should check that scanf succeeded too */
if (scanf("%9s", person->ads->city) != 1)
/* ^ prevent buffer overflow */
{
printf("Invalid, input\n");
free(person->ads);
free(person);
return -1;
}
printf("Name: %s\n", person->name);
printf("Code: %d\n", person->ads->code);
printf("City: %s\n", person->ads->city);
free(person->ads);
free(person);
return 0;
}

Answer 3

how can i allocate memory for my second structure?
For example the same way as you did for the first structure: allocate it from the heap
#include <stdlib.h>
#include <stdio.h>
struct address
{
int code;
char city[10];
};
struct student
{
char name[10];
struct address * ads;
};
int main(void)
{
struct student * person1 = malloc(sizeof * person1);
if (NULL == person1)
{
perror("malloc() failed for person1");
}
else
{
person1->ads = malloc(sizeof * person1->ads);
if (NULL == person1->ads)
{
perror("malloc() failed for person1->ads");
}
else
{
/* scan and print */
free(person1->ads);
}
free(person1);
}
}