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From: Thiago Adams <thiago.adams@gmail.com>
Newsgroups: comp.lang.c
Subject: "not-const" qualifier for C
Date: Wed, 24 Apr 2024 16:24:52 -0300
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Motivation sample:

struct X {
      const char* const type;
};

struct X * make_x(){
   struct X * p = malloc(sizeof *p);
   if (p)
   {

       p->type = strdup("X");  // *** error, type is const ***

       if (p->type == NULL)
       {
          free(p);
          p = NULL;
       }
   }
   return p; //ok
}

void print(struct X * p){
   prinf("%s", p->type);
}

void x_destroy(struct X * p)
{
    free(p->type); // *** warning const to non-const ***
}

Now consider we have the keyword "mutable" that removes const from 
struct members.


struct X {
      const char* const type;
};

struct X * make_x(){
   mutable struct X * p = malloc(sizeof *p);
   if (p)
   {
       p->type = strdup("X");  //OK
       if (p->type == NULL)
       {
          free(p);
          p = NULL;
       }
   }
   return p; //ok
}

void print(struct X * p){
   prinf("%s", p->type);
}

void x_destroy(mutable struct X * p)
{
    free(p->type); //no warning
}