> "char data[0]" is not supported by the C standard, it's a GNU extension I
> believe.
>
> You can use 'offsetof' to determine the offset of a structure member, you
> can do something like
>
> struct STRING
> {
> size_t length;
> char data[1];
> }
>
> struct STRING* build_string(size_t size, const char* data)
> {
> struct STRING* p = (struct STRING*)malloc(offsetof(struct STRING, data) +
> size);
> p->length = size;
> memcpy(p->data, data, size);
> return p;
"char data[0]" is not standard C, and "char data[]" is not standard C89.
Lua uses exactly the technique described here, with offsetof, to
allocate Udata, CClosure, and LClosure without wasting memory.
Postgres, per example, benefits from ARRAY_FLEXIBLE_MEMBER 0.
See at:
#define ARRAY_FLEXIBLE_MEMBER 1
Lua 5.4.2 Windows (64 bits)
type sizes (bytes):
Struct Size
lua_State 192
Proto 128
Table 56
Udata 48
CClosure 48
TString 40
Udata0 40
UpVal 40
LClosure 40
Node 24
NodeKey 24
TValue 16
GCObject 16
Upvaldesc 16
#define ARRAY_FLEXIBLE_MEMBER 0
Lua 5.4.2 Windows (64 bits)
type sizes (bytes):
Struct Size
lua_State 192
Proto 128
Table 56
Udata 32
CClosure 32
TString 40
Udata0 40
UpVal 40
LClosure 32
Node 24
NodeKey 24
TValue 16
GCObject 16
Upvaldesc 16
I was wrong, with ARRAY_FLEXIBLE_MEMBER 0, Lua reduces the structures by 16 bytes:
UData
CClosure
And, reduces the structure by 8 bytes:
LClosure
