Segmentation fault while using malloc with char pointers

Question

I am new to C and learning structs. I am trying to malloc a char pointer with size 30 but it is giving a segmentation fault(core dump). I searched it on the interne

Answer 1

The problem lies here.

str *p;   ---> Problem Line 1

p->f = (char*)malloc(sizeof(char)*30); ----> Problem  Line2
p->l = (char*)malloc(sizeof(char)*30);

You have declared a pointer p of type str.
Problem 1:
You have not initialized this pointer to NULL. Thus, p can point to anything.
Problem 2:
Since p is an uninitialized pointer, p->f can point anywhere which is causing the segfault. Below is the correct way

str *p = NULL;
p = malloc(sizeof(str));
// Check p for NULL
memset(p, 0, sizeof(str));

Now you have an initialized memory pointed by p. You are now free to use it as you want.