Re: Lua define ARRAY_FLEXIBLE

"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;

}

On Sun, Nov 13, 2022 at 6:02 AM Ranier Vilela <ranier.vf@gmail.com> wrote:

Lua could benefit from introducing ARRAY_FLEXIBLE_MEMBER define.

With C99 or greater, struct with array flexible member can be:
struct STRING_S
{
size_t size;
char data[];
};

Before C99, I think maybe it needs to be used with zero,
I haven't checked.

struct STRING_S
{
size_t size;
char data[0];
};

x86_64 plattform -O2
https://godbolt.org/z/PKP4hhMbe

#include <stdio.h>

struct STRING_S
{
size_t size;
char data[1];
};

typedef struct STRING_S string_t;

int main(void)
{
string_t str;

printf("size=%zu\n", sizeof(str));

return 0;
}

ASM generation compiler returned: 0
Execution build compiler returned: 0
Program returned: 0
size=16

So, some structs can be reduced by 8 bytes.

struct Udata
struct CClosure
struct LClosure