cjson源码剖析（1）

我就是我 2022-07-28 00:15 268阅读 0赞

# 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);