Modern C and What We Can Learn from It [video]

Post by belgesel » Sat, May 22, 2021, 5:28 PM UTC

an1sotropy wrote: post #130

belgesel wrote: post #128

Earlier quoted context omitted.

Although I disagree with some part of the presenter's ideas. I learned struct initializers and _Generic keyword from the presentation. So that is a great win for me. Now I can write safer code with the const and non-const pointer types. Suppose that I want to return a pointer to a field inside of a struct. Either I had to write const and non-const versions of the same function and use them which brings unreadable cod…

I just noticed your comment and I'm intrigued. Can you explain more or give a tiny example of this const/non-const flexibility?

Suppose I have the following struct and functions.

  struct my_struct{int a; char private[10];}
  void * get_struct_field_nonconst(struct my_struct *ptr)
  { return &(ptr->private[0]); }

With these elements you are only allowed to give non-const pointers to read or write inside private field. In order to truly apply this to const pointers (no casting etc.) you will need another get_struct_field() function but defined as this.

  const void * get_struct_field_const(const struct my_struct *ptr)
  { return &(ptr->private[0]); }

This will work but it is ugly. Here _Generic keyword allows you to write these functions but use them with a common name. Such as get_struct_field(). And that would be something like this:

  #define get_struct_field(ptr) \
  _Generic((ptr), \
  const struct my_struct * : get_struct_field_const, \
   struct my_struct * : get_struct_field_nonconst) \
  (ptr)

Hope this would help!

Post by an1sotropy » Fri, Jun 04, 2021, 3:48 PM UTC

belgesel wrote: post #131

an1sotropy wrote: post #130

Earlier quoted context omitted.

I just noticed your comment and I'm intrigued. Can you explain more or give a tiny example of this const/non-const flexibility?

Suppose I have the following struct and functions. struct my_struct{int a; char private[10];} void * get_struct_field_nonconst(struct my_struct *ptr) { return &(ptr->private[0]); } With these elements you are only allowed to give non-const pointers to read or write inside private field. In order to truly apply this to const pointers (no casting etc.) you will need another get_struct_field() function but defined as th…

(slow answer) yes, thanks for the example!)

Re: Modern C and What We Can Learn from It [video]

Re: Modern C and What We Can Learn from It [video]