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

As many people have pointed out, you need to allocate memory for that str struct, before writing the fields of it.

The best way to do so in C is:

p = malloc(sizeof *p);

This has the following advantages:

1. No cast, since no cast is needed in C and having a cast can hide actual errors.
2. No duplication of type information, by using the sizeof operator to compute how much storage is needed for the value p points at.

When you then allocate the string space, you can simplify it to:

p->f = malloc(30); 

Because:

1. No cast, for the very same reason.
2. C guarantees that sizeof (char) is always 1, so using it like you did adds nothing, 1 * 30 is always just 30.

Last, you should always check the return value of malloc() before using it, since it can fail and return NULL.