cJSON学习笔记

cJSON 总共有以下 8 种数据类型：

/* cJSON Types: */
/*
* 用 8-bit 表示 8 种数据类型
*/
#define cJSON_Invalid (0)
#define cJSON_False  (1 << 0)
#define cJSON_True   (1 << 1)
#define cJSON_NULL   (1 << 2)
#define cJSON_Number (1 << 3)
#define cJSON_String (1 << 4)
#define cJSON_Array  (1 << 5)
#define cJSON_Object (1 << 6)
#define cJSON_Raw    (1 << 7) /* raw json */

Hooks

该项目在调用内存分配、清理函数时用到了Hook技术。

1. 先定义 internal_hooks 数据结构，在结构体内声明 allocate,deallocate,reallocate这3个函数。

   typedef struct internal_hooks
   {
       /* 分配 */
       void *(CJSON_CDECL *allocate)(size_t size);
       /* 解除 */
       void (CJSON_CDECL *deallocate)(void *pointer);
       /* 重分配 */
       void *(CJSON_CDECL *reallocate)(void *pointer, size_t size);
   } internal_hooks;

2. 特殊处理 MSVC error C2322

   #if defined(_MSC_VER)
   /* work around MSVC error C2322: '...' address of dllimport '...' is not static */
   static void * CJSON_CDECL internal_malloc(size_t size)
   {
       return malloc(size);
   }
   static void CJSON_CDECL internal_free(void *pointer)
   {
       free(pointer);
   }
   static void * CJSON_CDECL internal_realloc(void *pointer, size_t size)
   {
       return realloc(pointer, size);
   }
   #else
   #define internal_malloc malloc
   #define internal_free free
   #define internal_realloc realloc
   #endif

3. 定义global_hooks

   static internal_hooks global_hooks = { internal_malloc, internal_free, internal_realloc };

4. 初始化global_hooks

   CJSON_PUBLIC(void) cJSON_InitHooks(cJSON_Hooks* hooks)
   {
       if (hooks == NULL)
       {
           /* 分配默认使用 malloc, free, realloc */
           /* Reset hooks */
           global_hooks.allocate = malloc;
           global_hooks.deallocate = free;
           global_hooks.reallocate = realloc;
           return;
       }
   
       /* 可自定义 hooks */
       global_hooks.allocate = malloc;
       if (hooks->malloc_fn != NULL)
       {
           global_hooks.allocate = hooks->malloc_fn;
       }
   
       global_hooks.deallocate = free;
       if (hooks->free_fn != NULL)
       {
           global_hooks.deallocate = hooks->free_fn;
       }
   
       /* use realloc only if both free and malloc are used */
       global_hooks.reallocate = NULL;
       if ((global_hooks.allocate == malloc) && (global_hooks.deallocate == free))
       {
           global_hooks.reallocate = realloc;
       }
   }