I have the following struct in C:
typedef struct
{
int age;
char name[20];
} Person;
in the main() I have:
Person *person;
person->age = 21;
This causes a segmentation fault, I have tried Googling but the resources that I have found do not have the struct declared as a pointer. I need this struct to be declared as a pointer so that it can be passed into another function. How would I properly access the members of this struct? (I also need to do this for char).
It is fairly straight forward, declare a pointer to struct, then allocate with malloc and assign/copy values:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct {
int age;
char name[20];
} Person;
void agingfunction (Person **p)
{
(*p)->age = 25;
}
int main (void) {
Person *p = malloc (sizeof *p);
if (!p) return 1;
p->age = 5;
strncpy (p->name, "Charles Darwin", 20);
printf ("\n %s is %d years old.\n", p->name, p->age);
agingfunction (&p);
printf ("\n %s is now %d years old.\n", p->name, p->age);
free (p);
return 0;
}
Output
$ ./bin/structinit
Charles Darwin is 5 years old.
Charles Darwin is now 25 years old.
You need to allocate memory for the struct somewhere. If you have a function like void func (Person* p); then you pass a struct to it like this:
Person person;
func(&person);
or equivalent:
Person person;
Person* ptr = &person;
func(ptr);
You have to allocate memory for your struct instantiation as:
Person *person = malloc(sizeof(Person));
else you can also declare as
Person person;
and assign values as,
person.age = 21;
In the main do:
Person *person=malloc (1 * sizeof (Person ));
person->age = 21;
You need allocate a real place in the memory for your object. Then, you can deal with it
If you want to use this pointer, you need to allocate memory with malloc first. Like so:
Person *person = malloc(sizeof(Person));
But in your code you can also do without the pointer, by declaring person normally, like this:
Person pers;
pers.age = 21;
Person* pointer = &pers;
malloc()