Object oriented programming in C (2007)(ldeniau.web.cern.ch)

    /* foo.h */
    #ifndef FOO_H
    #define FOO_H

    typedef struct _foo_ctx_t {
            int timeout;
            void *priv;
    } foo_ctx_t;

    #ifdef _cplusplus
    extern “C” {
    #endif

    foo_ctx_t *foo_init(foo_ctx_t *self);
    int foo_bar(foo_ctx_t *self);

    #ifdef _cplusplus
    }
    #endif

    #endif /* FOO_H */


    /* foo.c */
    #include “foo.h”

    #include <stdlib.h>

    #define PRIVATE(var) ((foo_private_ctx_t *)(self->priv)->(var))

    typedef struct _foo_private_ctx_t {
            int whatever;
    } foo_private_ctx_t;

    foo_ctx_t *
    foo_init(foo_ctx_t *self) {
            self->timeout = 1000;
            self->priv = malloc(sizeof(ctx_private_ctx_t));
            if (!self->priv) return NULL;
            PRIVATE(whatever) = 0;
            return self;
    }

    int
    foo_bar(foo_ctx_t *self) {
            PRIVATE(whatever) += self->timeout;
            return 1;
    }