C中的分段错误（核心转储）

Question

Code attached below. I tried to run the code, the values printed are correct but getting segmentation fault. Can anyone explain why?

#include <stdio.h>

typedef struct
{
    char name[30];
    int age;
} rec[2];

void main()
{
    rec g;
    rec *pt = &g;

    for (int i = 0; i < 2; i++)
    {
        printf("Enter name: ");
        scanf("%s", &pt[i]->name);
        printf("Enter age: ");
        scanf("%d", &pt[i]->age);
    }

    printf("Name\tAge\n");
    for (int i = 0; i < 2; ++i)
    {
        printf("%s\t", pt[i]->name);
        printf("%d\n", pt[i]->age);
    }

Output :

And also please explain the difference between

typedef struct {
    int a;
} example[3];

example v;

and

typedef struct {
    int a;
} example;

example v[3];

Answer 1

1. void main() is wrong. It has to be int main(void)
2. Here you have an example why hiding arrays behind the typedefs is a very bad habit. In your case pt[1] references the next array of two structs which outside the array bounds. You invoke undefined behaviour which can result in segfault.

You need to:

typedef struct
{
    char name[30];
    int age;
} rec[2];

int main()
{
    rec g;
    rec *pt = &g;

    for (int i = 0; i < 2; i++)
    {
        printf("Enter name: ");
        scanf("%s", pt[0][i].name);
        printf("Enter age: ");
        scanf("%d", &(pt[0][i].age));
    }

    printf("Name\tAge\n");
    for (int i = 0; i < 2; ++i)
    {
        printf("%s\t", pt[0][i].name);
        printf("%d\n", pt[0][i].age);
    }
}

The best way is to typedef struct and define the array.

typedef struct
{
    char name[30];
    int age;
} rec;

int main()
{
    rec pt[2];

    for (int i = 0; i < 2; i++)
    {
        printf("Enter name: ");
        scanf("%s", pt[i].name);
        printf("Enter age: ");
        scanf("%d", &(pt[i].age));
    }

    printf("Name\tAge\n");
    for (int i = 0; i < 2; ++i)
    {
        printf("%s\t", pt[i].name);
        printf("%d\n", pt[i].age);
    }
}