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

Regular expressions would work great about 90% of the time and then cause endless headaches for the remaining 10%.

The headaches happen in the cases where the C code contains syntax that you didn't think of when writing your regular expressions. Then you go back and realise that C can't really be parsed by regular expressions, and life becomes not fun.

Try turning it around: define your own simple format, which allows less tricks than C does, and generate both the C header file and the Python interface code from your file:

define socketopts
    int16 port
    int32 ipv4address
    int32 flags

Then you can easily write some Python to convert this to:

typedef struct {
    short port;
    int ipv4address;
    int flags;
} socketopts;

and also to emit a Python class which uses struct to pack/unpack three values (possibly two of them big-endian and the other native-endian, up to you).

Answer 2

One my friend for this tasks done C-parser which he use with cog.

Answer 3

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.

Answer 4

Have you looked at Swig?

Answer 5

I have quite successfully used GCCXML on fairly large projects. You get an XML representation of the C code (including structures) which you can post-process with some simple Python.

Answer 6

ctypes-codegen or ctypeslib (same thing, I think) will generate ctypes Structure definitions (also other things, I believe, but I only tried structs) by parsing header files using GCCXML. It's no longer supported, but will likely work in some cases.