cjson源码剖析（1）

cJSON类型

    /* cJSON Types: */#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_IsReference 256#define cJSON_StringIsConst 512

前面七个是cJSON支持的七种类型

cJSON结构

    /* The cJSON structure: */    typedef struct cJSON {        struct cJSON *next,*prev;   /* next/prev allow you to walk array/object chains. Alternatively, use GetArraySize/GetArrayItem/GetObjectItem */        struct cJSON *child;        /* An array or object item will have a child pointer pointing to a chain of the items in the array/object. */        int type;                   /* The type of the item, as above. */        char *valuestring;          /* The item's string, if type==cJSON_String */        int valueint;               /* The item's number, if type==cJSON_Number */        double valuedouble;         /* The item's number, if type==cJSON_Number */        char *string;               /* The item's name string, if this item is the child of, or is in the list of subitems of an object. */    } cJSON;

1. struct cJSON *next,*prev;用于指向同级对象
2. struct cJSON *child;如果一个对象是一个对象集合或者是对象数组，该指针指向存储对象集合或者是对象数组
3. int type;即 /* cJSON Types: */
4. char *valuestring;int valueint;double valuedouble;存储对应值
5. char *string;该值的对象名字。。

cJSON接口

    typedef struct cJSON_Hooks {        void *(*malloc_fn)(size_t sz);        void (*free_fn)(void *ptr);    } cJSON_Hooks;    //释放/申请用    /* Supply malloc, realloc and free functions to cJSON */    extern void cJSON_InitHooks(cJSON_Hooks* hooks);    //初始化cJSON_Hooks    /* Supply a block of JSON, and this returns a cJSON object you can interrogate. Call cJSON_Delete when finished. */    extern cJSON *cJSON_Parse(const char *value);    //将json格式的字符串转换成cJSON对象    /* Render a cJSON entity to text for transfer/storage. Free the char* when finished. */    extern char  *cJSON_Print(cJSON *item);    //将cJSON对象转换成json格式的字符串    /* Render a cJSON entity to text for transfer/storage without any formatting. Free the char* when finished. */    extern char  *cJSON_PrintUnformatted(cJSON *item);    //输出无格式化字符串，不太懂    /* Render a cJSON entity to text using a buffered strategy. prebuffer is a guess at the final size. guessing well reduces reallocation. fmt=0 gives unformatted, =1 gives formatted */    extern char *cJSON_PrintBuffered(cJSON *item,int prebuffer,int fmt);    //还是不懂。似乎是可以选择式，提前申请的char空间为prebuffer，然后可以减少realloc次数    /* Delete a cJSON entity and all subentities. */    extern void   cJSON_Delete(cJSON *c);    //删除cJSON对象    /* Returns the number of items in an array (or object). */    extern int    cJSON_GetArraySize(cJSON *array);    //获得JSON数组对象个数    /* Retrieve item number "item" from array "array". Returns NULL if unsuccessful. */    extern cJSON *cJSON_GetArrayItem(cJSON *array,int item);    //获得数组中第item 的对象    /* Get item "string" from object. Case insensitive. */    extern cJSON *cJSON_GetObjectItem(cJSON *object,const char *string);    //取得名字为‘string’的该对象    extern int cJSON_HasObjectItem(cJSON *object,const char *string);    //看有没有名字为'string'的该对象    /* For analysing failed parses. This returns a pointer to the parse error. You'll probably need to look a few chars back to make sense of it. Defined when cJSON_Parse() returns 0. 0 when cJSON_Parse() succeeds. */    extern const char *cJSON_GetErrorPtr(void);    //没看懂，好像是cJSON_Parse失败后用，用于查看是哪里格式不对，得看代码才知道    /* These calls create a cJSON item of the appropriate type. */    extern cJSON *cJSON_CreateNull(void);    extern cJSON *cJSON_CreateTrue(void);    extern cJSON *cJSON_CreateFalse(void);    extern cJSON *cJSON_CreateBool(int b);    extern cJSON *cJSON_CreateNumber(double num);    extern cJSON *cJSON_CreateString(const char *string);    extern cJSON *cJSON_CreateArray(void);    extern cJSON *cJSON_CreateObject(void);    //创建对象    /* These utilities create an Array of count items. */    extern cJSON *cJSON_CreateIntArray(const int *numbers,int count);    extern cJSON *cJSON_CreateFloatArray(const float *numbers,int count);    extern cJSON *cJSON_CreateDoubleArray(const double *numbers,int count);    extern cJSON *cJSON_CreateStringArray(const char **strings,int count);    //创建对象数组    /* Append item to the specified array/object. */    extern void cJSON_AddItemToArray(cJSON *array, cJSON *item);    extern void cJSON_AddItemToObject(cJSON *object,const char *string,cJSON *item);    extern void cJSON_AddItemToObjectCS(cJSON *object,const char *string,cJSON *item);    //添加    /* Use this when string is definitely const (i.e. a literal, or as good as), and will definitely survive the cJSON object */    /* Append reference to item to the specified array/object. Use this when you want to add an existing cJSON to a new cJSON, but don't want to corrupt your existing cJSON. */    extern void cJSON_AddItemReferenceToArray(cJSON *array, cJSON *item);    extern void cJSON_AddItemReferenceToObject(cJSON *object,const char *string,cJSON *item);    /* Remove/Detatch items from Arrays/Objects. */    extern cJSON *cJSON_DetachItemFromArray(cJSON *array,int which);    extern void   cJSON_DeleteItemFromArray(cJSON *array,int which);    extern cJSON *cJSON_DetachItemFromObject(cJSON *object,const char *string);    extern void   cJSON_DeleteItemFromObject(cJSON *object,const char *string);    //删除对象    /* Update array items. */    extern void cJSON_InsertItemInArray(cJSON *array,int which,cJSON *newitem); /* Shifts pre-existing items to the right. */    extern void cJSON_ReplaceItemInArray(cJSON *array,int which,cJSON *newitem);    extern void cJSON_ReplaceItemInObject(cJSON *object,const char *string,cJSON *newitem);    //替换对象    /* Duplicate a cJSON item */    extern cJSON *cJSON_Duplicate(cJSON *item,int recurse);    /* Duplicate will create a new, identical cJSON item to the one you pass, in new memory that will     need to be released. With recurse!=0, it will duplicate any children connected to the item.     The item->next and ->prev pointers are always zero on return from Duplicate. */    /* ParseWithOpts allows you to require (and check) that the JSON is null terminated, and to retrieve the pointer to the final byte parsed. */    extern cJSON *cJSON_ParseWithOpts(const char *value,const char **return_parse_end,int require_null_terminated);    extern void cJSON_Minify(char *json);