Re: When Immutability and Nullability Meet: Exploring Mutable Objects in C

On 17/09/2024 18:27, Thiago Adams wrote:

 I found some use cases where we may want disable const and _not_null (if C had this qualifier) at same time. Kind of "anti-qualifier".

I think
I think my post might not have any replies because it's too long. So here's a shorter version.
Consider this sample: It has a error and a warning
#include <stdlib.h>
#include <string.h>
struct person {
   const char* const name;
};
struct person * make(const char* name)
{
   struct person * p = malloc(sizeof *p);
   if (p == 0) return 0;
   p->name = strdup(name);  //error read-only
   return p;
}
void person_delete(struct person* p) {
     free(p->name); //warning
}
int main()
{
   const struct person * p = make("a");
   if (p){
      person_delete(p); //warning
   }
   return 0;
}
My suggestion is remove the error and warning by adding a new qualifier mutable
mutable struct person * p = malloc(sizeof *p);
That allows p->name to be changed and person_delete to be called with no warnings.
void person_delete(mutable struct person* p) {
     free(p->name); //ok
}
https://godbolt.org/z/5Yo63ab1Y