Chia module và đóng gói

/* 1. No chiu trach nhiem VE cai gi?
      Neu ban tra loi bang mot cau co chu "va" thi no lam qua nhieu.

      "quan ly danh sach sinh vien VA doc tep VA in bao cao"
      -> ba module: danh_sach.c, doc_tep.c, bao_cao.c

   2. No CAN nhung gi tu ben ngoai?
      Cang it cang tot. Mot module chi phu thuoc vao thu vien chuan
      la mot module ban kiem thu duoc de dang.

   3. No LO ra nhung gi?
      Dem so ky hieu trong header. Neu hon 20 thi hoac module qua
      to, hoac ban dang lo ra chi tiet ben trong. */

/* ds.h, cong khai */
#ifndef DS_H
#define DS_H
#include <stddef.h>

typedef struct Ds Ds;           /* ten thay duoc, noi dung KHONG */

Ds     *ds_tao(size_t suc_chua_dau);
void    ds_huy(Ds *d);
int     ds_them(Ds *d, int x);
size_t  ds_so_luong(const Ds *d);

#endif


/* ds.c, hien thuc */
#include "ds.h"
#include <stdlib.h>

struct Ds {                     /* dinh nghia CHI o day */
    int    *pt;
    size_t  co;
    size_t  suc_chua;
};

Ds *ds_tao(size_t suc_chua_dau) { ... }
size_t ds_so_luong(const Ds *d) { return d->co; }

#ifndef DU_AN_DS_H          /* bao ve: TIEN TO DU AN + duong dan */
#define DU_AN_DS_H

/* 1. Include TOI THIEU can cho chinh header nay */
#include <stddef.h>         /* size_t */

/* 2. Khai bao truoc thay cho include khi chi can con tro */
typedef struct CauHinh CauHinh;

/* 3. Kieu cong khai */
typedef struct Ds Ds;

/* 4. Hang so cong khai */
#define DS_TOI_DA 1000000

/* 5. Ham, kem tai lieu ngan */

/**
 * Tao mot danh sach rong.
 * @param suc_chua_dau  so phan tu cap truoc, 0 nghia la mac dinh
 * @return  con tro moi, hoac NULL neu het bo nho
 *          Nguoi goi PHAI goi ds_huy.
 */
Ds *ds_tao(size_t suc_chua_dau);

/** Giai phong. An toan voi NULL. */
void ds_huy(Ds *d);

/**
 * Them mot phan tu vao cuoi.
 * @return 0 thanh cong, -1 het bo nho, -2 vuot DS_TOI_DA
 */
int ds_them(Ds *d, int x);

#endif /* DU_AN_DS_H */

/* vong_a.h */
#ifndef VONG_A_H
#define VONG_A_H
#include "vong_b.h"                     /* A can B */
typedef struct { B *b; int x; } A;
A   *a_tao(void);
void a_dung_b(A *a);
#endif

/* vong_b.h */
#ifndef VONG_B_H
#define VONG_B_H
#include "vong_a.h"                     /* B can A: VONG */
typedef struct { A *a; int y; } B;
B   *b_tao(void);
void b_dung_a(B *b);
#endif

/* TRUOC: mang.c goi giao_dien_ve() -> mang phu thuoc giao dien
           giao_dien.c goi mang_gui()      -> giao dien phu thuoc mang
   VONG. */

/* SAU: mang.h khong biet gi ve giao dien */
typedef void (*HamNhan)(const char *tin, void *ctx);

void mang_dat_ham_nhan(HamNhan f, void *ctx);
int  mang_gui(const char *tin);

/* mang.c */
static HamNhan g_nhan;
static void   *g_ctx;

void mang_dat_ham_nhan(HamNhan f, void *ctx) { g_nhan = f; g_ctx = ctx; }

static void khi_co_tin(const char *tin) {
    if (g_nhan) g_nhan(tin, g_ctx);     /* khong biet ai se nhan */
}

/* giao_dien.c */
#include "mang.h"
static void hien_thi(const char *tin, void *ctx) { ... }

void giao_dien_khoi_tao(void) {
    mang_dat_ham_nhan(hien_thi, NULL);  /* giao dien -> mang, MOT chieu */
}

/* Bay gio do thi la:  giao_dien.c -> mang.h
   Khong con vong, va mang.c kiem thu duoc ma khong can giao dien. */