C const behavior

gcc.log

q.c: In function ‘main’:
q.c:6:10: error: assignment of read-only location ‘*a’
    6 |     a[0] = 'H';
      |          ^
q.c:7:10: warning: passing argument 1 of ‘free’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
    7 |     free(a);
      |          ^
In file included from q.c:1:
/usr/include/stdlib.h:687:25: note: expected ‘void *’ but argument is of type ‘const char *’
  687 | extern void free (void *__ptr) __THROW;
      |                   ~~~~~~^~~~~
q.c:12:10: error: assignment of read-only location ‘*a’
   12 |     a[0] = 'H';
      |          ^
q.c:13:10: warning: passing argument 1 of ‘free’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
   13 |     free(a);
      |          ^
/usr/include/stdlib.h:687:25: note: expected ‘void *’ but argument is of type ‘const char *’
  687 | extern void free (void *__ptr) __THROW;
      |                   ~~~~~~^~~~~

q.c

#include <stdlib.h>

int main() {
  {
    const char *a = malloc(4);
    a[0] = 'H';
    free(a);
  }

  {
    char const *a = malloc(4);
    a[0] = 'H';
    free(a);
  }

  {
    char * const a = malloc(4);
    a[0] = 'H';
    free(a);
  }

  return 0;
}