4 ms·

"C is a weak, statically typed language" Wouldn't that imply that a variable of one type could be coerced into another type? I would say C is strong typed...

kscaldef 14y ago
C is weakly-typed. You can cast anything to anything else and the compiler won't stop you.
- pimentel 14y ago
  That's right! Completely forgot about the cast.
  - dakimov 14y ago
    The worse thing is that you can address a memory location and interpret it as another type (aliasing).
emeraldd 14y ago
> Wouldn't that imply that a variable of one type could be coerced into another type? Yup! It's quite common to cast things from a void * to a more specific one. You do it every time you call malloc.
dspeyer 14y ago
int i; float f = *(float*)&i; I'm not saying you should do this, but you can. Or to use an example the author didn't regret: struct foo { int a; int b; int c; }__attribute__((packed)); void print(foo* f) { int *p = f; int i; for (i=0; i<sizeof(foo)/sizeof(int); i++) { printf("%d,",p[i]); } }
- emeraldd 14y ago
  Here's one I used in a GC implementation a while back. That last 'uint_8t obj[]' is used to hold the object that was actually allocated. struct meta_obj { meta_obj_type *next; // next object in our list mark_type mark; size_t size; gc_type_def type_def; uint8_t obj[]; // contained object }; Or another (contrived) example: struct obj_type { obj_type_enum type; }; struct string_obj_type { obj_type_enum type; char *c; }; You start with a collection of obj_type pointers and cast them to the appropriate pointer type when you have identified the actual contained struct. Useful if you need to have a heterogeneous list of things.
  - chj 14y ago
    Is this standard? I mean the unknown size field 'obj'.
    - dagw 14y ago
      It was added to the C99 standard.

kscaldef 14y ago

C is weakly-typed. You can cast anything to anything else and the compiler won't stop you.

pimentel 14y ago
That's right! Completely forgot about the cast.
- dakimov 14y ago
  The worse thing is that you can address a memory location and interpret it as another type (aliasing).

emeraldd 14y ago

> Wouldn't that imply that a variable of one type could be coerced into another type? Yup! It's quite common to cast things from a void * to a more specific one. You do it every time you call malloc.

dspeyer 14y ago

int i; float f = *(float*)&i; I'm not saying you should do this, but you can. Or to use an example the author didn't regret: struct foo { int a; int b; int c; }__attribute__((packed)); void print(foo* f) { int *p = f; int i; for (i=0; i<sizeof(foo)/sizeof(int); i++) { printf("%d,",p[i]); } }

emeraldd 14y ago
Here's one I used in a GC implementation a while back. That last 'uint_8t obj[]' is used to hold the object that was actually allocated. struct meta_obj { meta_obj_type *next; // next object in our list mark_type mark; size_t size; gc_type_def type_def; uint8_t obj[]; // contained object }; Or another (contrived) example: struct obj_type { obj_type_enum type; }; struct string_obj_type { obj_type_enum type; char *c; }; You start with a collection of obj_type pointers and cast them to the appropriate pointer type when you have identified the actual contained struct. Useful if you need to have a heterogeneous list of things.
- chj 14y ago
  Is this standard? I mean the unknown size field 'obj'.
  - dagw 14y ago
    It was added to the C99 standard.