Extract the fields of a C struct

Question

I often have to write code in other languages that interact with C structs. Most typically this involves writing Python code with the struct or ctypes modules.

So I

Answer 1

If you compile your C code with debugging (-g), pahole (git) can give you the exact structure layouts being used.

$ pahole /bin/dd
…
struct option {
        const char  *              name;                 /*     0     8 */
        int                        has_arg;              /*     8     4 */

        /* XXX 4 bytes hole, try to pack */

        int *                      flag;                 /*    16     8 */
        int                        val;                  /*    24     4 */

        /* size: 32, cachelines: 1, members: 4 */
        /* sum members: 24, holes: 1, sum holes: 4 */
        /* padding: 4 */
        /* last cacheline: 32 bytes */
};
…

This should be quite a lot nicer to parse than straight C.