C语言与面向对象

问题一:C++的private关键字主要作用是封装,那么C语言如何完成同样的需求?

答:封装就是不给人看到,依着这个思路,我们来看看优秀的代码是怎么实现的.

apache里的内存池这一概念,它的声明在apr_pool.h里,

/** The fundamental pool type */
typedef struct apr_pool_t apr_pool_t;

而它的定义却在apr_pool.c里,

struct apr_pool_t {
apr_pool_t *parent;
apr_pool_t *child;
apr_pool_t *sibling;
apr_pool_t **ref;
cleanup_t *cleanups;
cleanup_t *free_cleanups;
apr_allocator_t *allocator;
struct process_chain *subprocesses;
apr_abortfunc_t abort_fn;
apr_hash_t *user_data;
const char *tag;

#if !APR_POOL_DEBUG
apr_memnode_t *active;
apr_memnode_t *self; /* The node containing the pool itself */
char *self_first_avail;

#else /* APR_POOL_DEBUG */
apr_pool_t *joined; /* the caller has guaranteed that this pool
* will survive as long as ->joined */
debug_node_t *nodes;
const char *file_line;
apr_uint32_t creation_flags;
unsigned int stat_alloc;
unsigned int stat_total_alloc;
unsigned int stat_clear;
#if APR_HAS_THREADS
apr_os_thread_t owner;
apr_thread_mutex_t *mutex;
#endif /* APR_HAS_THREADS */
#endif /* APR_POOL_DEBUG */
#ifdef NETWARE
apr_os_proc_t owner_proc;
#endif /* defined(NETWARE) */
cleanup_t *pre_cleanups;
cleanup_t *free_pre_cleanups;
};

这样做的好处是外界(也即指apr_pool.c以外的文件)无法直接访问内存池的成员.内存池只提供类似这样的接口:

apr_pool_create(&ptemp, pconf);
apr_pool_tag(ptemp, "ptemp");

apr_pool_clear(plog);

apr_pool_destroy(ptemp);
apr_pool_lock(pconf, 1);

这样的是不是很像C++里的public和private的运用.

同样道理,在apr_pool_t里有一个成员cleanups,我们可以看到它的定义和声明都在apr_pool.c里,

typedef struct cleanup_t cleanup_t;

struct cleanup_t {
struct cleanup_t *next;
const void *data;
apr_status_t (*plain_cleanup_fn)(void *data);
apr_status_t (*child_cleanup_fn)(void *data);
};

这样做,一般的apache开发者根本都不知道有struct cleanup_t这种东西.