2025年2月24日 星期一 甲辰(龙)年 腊月廿四 设为首页 加入收藏
rss
您当前的位置:首页 > 计算机 > 编程开发 > C语言

CJSON简单介绍

时间:07-30来源:作者:点击数:31
城东书院 www.cdsy.xyz

json简介

JSON(JavaScript Object Notation) 是一种轻量级的数据交换格式。 易于人阅读和编写。同时也易于机器解析和生成。 它基于JavaScript Programming Language, Standard ECMA-262 3rd Edition - December 1999的一个子集,最新的定义可以参考ECMA-404_2nd_edition_The JSON Data Interchange Syntax,这份标准只有16页,可以一次性读完。

JSON具有以下这些形式:

  • 对象是一个无序的“‘名称/值’对”集合。一个对象以 { 左括号 \{_{左括号}{左括号​ 开始, } 右括号 \}_{右括号}}右括号​ 结束。每个“名称”后跟一个 : 冒号 :_{冒号}:冒号​ ;“‘名称/值’ 对”之间使用 , 逗号 ,_{逗号},逗号​ 分隔。
  • 数组是值(value)的有序集合。一个数组以 [ 左中括号 [_{左中括号}[左中括号​ 开始, ] 右中括号 ]_{右中括号}]右中括号​ 结束。值之间使用 ,逗号 分隔。
  • 值(value)可以是双引号括起来的字符串(string)、数值(number)、true、false、 null、对象(object)或者数组(array)。这些结构可以嵌套。
  • 字符串(string)是由双引号包围的任意数量Unicode字符的集合,使用反斜线转义。一个字符(character)即一个单独的字符串(character string)。
  • 数值(number)也与C或者Java的数值非常相似。除去未曾使用的八进制与十六进制格式。除去一些编码细节。
  • 空白可以加入到任何符号之间。
    一个典型的json结构如下所示
  • {
  • "FirstName": "John",
  • "LastName": "Doe",
  • "Age": 43,
  • "Address": {
  • "Street": "Downing Street 10",
  • "City": "London",
  • "Country": "Great Britain"
  • },
  • "Phone numbers": [
  • "+44 1234567",
  • "+44 2345678"
  • ]
  • }

具体可以参考jason官网:http://www.json.org/json-zh.html

CJSON

CJSON是一个基于C语言实现的json库,为了兼容更多的平台,使用ANSI C (C89)标准来编写,其项目地址在http://github.com/DaveGamble/cJSON。

如何在项目中使用CJSON

有两种方式:

  1. 使用链接库的方式,先编译成库,之后在项目中使用
  2. 直接将CJSON的源代码(cJSON.hcJSON.c)加到项目中,之后和项目一起编译
CJSON提供的接口

CJSON提供的接口都在cJSON.h中声明出来了(以CJSON_PUBLIC的宏开头),还有一些直接是宏

  • /* returns the version of cJSON as a string */
  • CJSON_PUBLIC(const char*) cJSON_Version(void);
  • /* Supply malloc, realloc and free functions to cJSON */
  • CJSON_PUBLIC(void) cJSON_InitHooks(cJSON_Hooks* hooks);
  • /* Memory Management: the caller is always responsible to free the results from all variants of cJSON_Parse (with cJSON_Delete) and cJSON_Print (with stdlib free, cJSON_Hooks.free_fn, or cJSON_free as appropriate). The exception is cJSON_PrintPreallocated, where the caller has full responsibility of the buffer. */
  • /* Supply a block of JSON, and this returns a cJSON object you can interrogate. */
  • CJSON_PUBLIC(cJSON *) cJSON_Parse(const char *value);
  • CJSON_PUBLIC(cJSON *) cJSON_ParseWithLength(const char *value, size_t buffer_length);
  • /* ParseWithOpts allows you to require (and check) that the JSON is null terminated, and to retrieve the pointer to the final byte parsed. */
  • /* If you supply a ptr in return_parse_end and parsing fails, then return_parse_end will contain a pointer to the error so will match cJSON_GetErrorPtr(). */
  • CJSON_PUBLIC(cJSON *) cJSON_ParseWithOpts(const char *value, const char **return_parse_end, cJSON_bool require_null_terminated);
  • CJSON_PUBLIC(cJSON *) cJSON_ParseWithLengthOpts(const char *value, size_t buffer_length, const char **return_parse_end, cJSON_bool require_null_terminated);
  • /* Render a cJSON entity to text for transfer/storage. */
  • CJSON_PUBLIC(char *) cJSON_Print(const cJSON *item);
  • /* Render a cJSON entity to text for transfer/storage without any formatting. */
  • CJSON_PUBLIC(char *) cJSON_PrintUnformatted(const cJSON *item);
  • /* 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 */
  • CJSON_PUBLIC(char *) cJSON_PrintBuffered(const cJSON *item, int prebuffer, cJSON_bool fmt);
  • /* Render a cJSON entity to text using a buffer already allocated in memory with given length. Returns 1 on success and 0 on failure. */
  • /* NOTE: cJSON is not always 100% accurate in estimating how much memory it will use, so to be safe allocate 5 bytes more than you actually need */
  • CJSON_PUBLIC(cJSON_bool) cJSON_PrintPreallocated(cJSON *item, char *buffer, const int length, const cJSON_bool format);
  • /* Delete a cJSON entity and all subentities. */
  • CJSON_PUBLIC(void) cJSON_Delete(cJSON *item);
  • /* Returns the number of items in an array (or object). */
  • CJSON_PUBLIC(int) cJSON_GetArraySize(const cJSON *array);
  • /* Retrieve item number "index" from array "array". Returns NULL if unsuccessful. */
  • CJSON_PUBLIC(cJSON *) cJSON_GetArrayItem(const cJSON *array, int index);
  • /* Get item "string" from object. Case insensitive. */
  • CJSON_PUBLIC(cJSON *) cJSON_GetObjectItem(const cJSON * const object, const char * const string);
  • CJSON_PUBLIC(cJSON *) cJSON_GetObjectItemCaseSensitive(const cJSON * const object, const char * const string);
  • CJSON_PUBLIC(cJSON_bool) cJSON_HasObjectItem(const cJSON *object, const char *string);
  • /* 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. */
  • CJSON_PUBLIC(const char *) cJSON_GetErrorPtr(void);
  • /* Check item type and return its value */
  • CJSON_PUBLIC(char *) cJSON_GetStringValue(const cJSON * const item);
  • CJSON_PUBLIC(double) cJSON_GetNumberValue(const cJSON * const item);
  • /* These functions check the type of an item */
  • CJSON_PUBLIC(cJSON_bool) cJSON_IsInvalid(const cJSON * const item);
  • CJSON_PUBLIC(cJSON_bool) cJSON_IsFalse(const cJSON * const item);
  • CJSON_PUBLIC(cJSON_bool) cJSON_IsTrue(const cJSON * const item);
  • CJSON_PUBLIC(cJSON_bool) cJSON_IsBool(const cJSON * const item);
  • CJSON_PUBLIC(cJSON_bool) cJSON_IsNull(const cJSON * const item);
  • CJSON_PUBLIC(cJSON_bool) cJSON_IsNumber(const cJSON * const item);
  • CJSON_PUBLIC(cJSON_bool) cJSON_IsString(const cJSON * const item);
  • CJSON_PUBLIC(cJSON_bool) cJSON_IsArray(const cJSON * const item);
  • CJSON_PUBLIC(cJSON_bool) cJSON_IsObject(const cJSON * const item);
  • CJSON_PUBLIC(cJSON_bool) cJSON_IsRaw(const cJSON * const item);
  • /* These calls create a cJSON item of the appropriate type. */
  • CJSON_PUBLIC(cJSON *) cJSON_CreateNull(void);
  • CJSON_PUBLIC(cJSON *) cJSON_CreateTrue(void);
  • CJSON_PUBLIC(cJSON *) cJSON_CreateFalse(void);
  • CJSON_PUBLIC(cJSON *) cJSON_CreateBool(cJSON_bool boolean);
  • CJSON_PUBLIC(cJSON *) cJSON_CreateNumber(double num);
  • CJSON_PUBLIC(cJSON *) cJSON_CreateString(const char *string);
  • /* raw json */
  • CJSON_PUBLIC(cJSON *) cJSON_CreateRaw(const char *raw);
  • CJSON_PUBLIC(cJSON *) cJSON_CreateArray(void);
  • CJSON_PUBLIC(cJSON *) cJSON_CreateObject(void);
  • /* Create a string where valuestring references a string so
  • * it will not be freed by cJSON_Delete */
  • CJSON_PUBLIC(cJSON *) cJSON_CreateStringReference(const char *string);
  • /* Create an object/array that only references it's elements so
  • * they will not be freed by cJSON_Delete */
  • CJSON_PUBLIC(cJSON *) cJSON_CreateObjectReference(const cJSON *child);
  • CJSON_PUBLIC(cJSON *) cJSON_CreateArrayReference(const cJSON *child);
  • /* These utilities create an Array of count items.
  • * The parameter count cannot be greater than the number of elements in the number array, otherwise array access will be out of bounds.*/
  • CJSON_PUBLIC(cJSON *) cJSON_CreateIntArray(const int *numbers, int count);
  • CJSON_PUBLIC(cJSON *) cJSON_CreateFloatArray(const float *numbers, int count);
  • CJSON_PUBLIC(cJSON *) cJSON_CreateDoubleArray(const double *numbers, int count);
  • CJSON_PUBLIC(cJSON *) cJSON_CreateStringArray(const char *const *strings, int count);
  • /* Append item to the specified array/object. */
  • CJSON_PUBLIC(cJSON_bool) cJSON_AddItemToArray(cJSON *array, cJSON *item);
  • CJSON_PUBLIC(cJSON_bool) cJSON_AddItemToObject(cJSON *object, const char *string, cJSON *item);
  • /* Use this when string is definitely const (i.e. a literal, or as good as), and will definitely survive the cJSON object.
  • * WARNING: When this function was used, make sure to always check that (item->type & cJSON_StringIsConst) is zero before
  • * writing to `item->string` */
  • CJSON_PUBLIC(cJSON_bool) cJSON_AddItemToObjectCS(cJSON *object, const char *string, cJSON *item);
  • /* 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. */
  • CJSON_PUBLIC(cJSON_bool) cJSON_AddItemReferenceToArray(cJSON *array, cJSON *item);
  • CJSON_PUBLIC(cJSON_bool) cJSON_AddItemReferenceToObject(cJSON *object, const char *string, cJSON *item);
  • /* Remove/Detach items from Arrays/Objects. */
  • CJSON_PUBLIC(cJSON *) cJSON_DetachItemViaPointer(cJSON *parent, cJSON * const item);
  • CJSON_PUBLIC(cJSON *) cJSON_DetachItemFromArray(cJSON *array, int which);
  • CJSON_PUBLIC(void) cJSON_DeleteItemFromArray(cJSON *array, int which);
  • CJSON_PUBLIC(cJSON *) cJSON_DetachItemFromObject(cJSON *object, const char *string);
  • CJSON_PUBLIC(cJSON *) cJSON_DetachItemFromObjectCaseSensitive(cJSON *object, const char *string);
  • CJSON_PUBLIC(void) cJSON_DeleteItemFromObject(cJSON *object, const char *string);
  • CJSON_PUBLIC(void) cJSON_DeleteItemFromObjectCaseSensitive(cJSON *object, const char *string);
  • /* Update array items. */
  • CJSON_PUBLIC(cJSON_bool) cJSON_InsertItemInArray(cJSON *array, int which, cJSON *newitem); /* Shifts pre-existing items to the right. */
  • CJSON_PUBLIC(cJSON_bool) cJSON_ReplaceItemViaPointer(cJSON * const parent, cJSON * const item, cJSON * replacement);
  • CJSON_PUBLIC(cJSON_bool) cJSON_ReplaceItemInArray(cJSON *array, int which, cJSON *newitem);
  • CJSON_PUBLIC(cJSON_bool) cJSON_ReplaceItemInObject(cJSON *object,const char *string,cJSON *newitem);
  • CJSON_PUBLIC(cJSON_bool) cJSON_ReplaceItemInObjectCaseSensitive(cJSON *object,const char *string,cJSON *newitem);
  • /* Duplicate a cJSON item */
  • CJSON_PUBLIC(cJSON *) cJSON_Duplicate(const cJSON *item, cJSON_bool 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. */
  • /* Recursively compare two cJSON items for equality. If either a or b is NULL or invalid, they will be considered unequal.
  • * case_sensitive determines if object keys are treated case sensitive (1) or case insensitive (0) */
  • CJSON_PUBLIC(cJSON_bool) cJSON_Compare(const cJSON * const a, const cJSON * const b, const cJSON_bool case_sensitive);
  • /* Minify a strings, remove blank characters(such as ' ', '\t', '\r', '\n') from strings.
  • * The input pointer json cannot point to a read-only address area, such as a string constant,
  • * but should point to a readable and writable address area. */
  • CJSON_PUBLIC(void) cJSON_Minify(char *json);
  • /* Helper functions for creating and adding items to an object at the same time.
  • * They return the added item or NULL on failure. */
  • CJSON_PUBLIC(cJSON*) cJSON_AddNullToObject(cJSON * const object, const char * const name);
  • CJSON_PUBLIC(cJSON*) cJSON_AddTrueToObject(cJSON * const object, const char * const name);
  • CJSON_PUBLIC(cJSON*) cJSON_AddFalseToObject(cJSON * const object, const char * const name);
  • CJSON_PUBLIC(cJSON*) cJSON_AddBoolToObject(cJSON * const object, const char * const name, const cJSON_bool boolean);
  • CJSON_PUBLIC(cJSON*) cJSON_AddNumberToObject(cJSON * const object, const char * const name, const double number);
  • CJSON_PUBLIC(cJSON*) cJSON_AddStringToObject(cJSON * const object, const char * const name, const char * const string);
  • CJSON_PUBLIC(cJSON*) cJSON_AddRawToObject(cJSON * const object, const char * const name, const char * const raw);
  • CJSON_PUBLIC(cJSON*) cJSON_AddObjectToObject(cJSON * const object, const char * const name);
  • CJSON_PUBLIC(cJSON*) cJSON_AddArrayToObject(cJSON * const object, const char * const name);
  • /* When assigning an integer value, it needs to be propagated to valuedouble too. */
  • #define cJSON_SetIntValue(object, number) ((object) ? (object)->valueint = (object)->valuedouble = (number) : (number))
  • /* helper for the cJSON_SetNumberValue macro */
  • CJSON_PUBLIC(double) cJSON_SetNumberHelper(cJSON *object, double number);
  • #define cJSON_SetNumberValue(object, number) ((object != NULL) ? cJSON_SetNumberHelper(object, (double)number) : (number))
  • /* Change the valuestring of a cJSON_String object, only takes effect when type of object is cJSON_String */
  • CJSON_PUBLIC(char*) cJSON_SetValuestring(cJSON *object, const char *valuestring);
  • /* If the object is not a boolean type this does nothing and returns cJSON_Invalid else it returns the new type*/
  • #define cJSON_SetBoolValue(object, boolValue) ( \
  • (object != NULL && ((object)->type & (cJSON_False|cJSON_True))) ? \
  • (object)->type=((object)->type &(~(cJSON_False|cJSON_True)))|((boolValue)?cJSON_True:cJSON_False) : \
  • cJSON_Invalid\
  • )
  • /* Macro for iterating over an array or object */
  • #define cJSON_ArrayForEach(element, array) for(element = (array != NULL) ? (array)->child : NULL; element != NULL; element = element->next)
  • /* malloc/free objects using the malloc/free functions that have been set with cJSON_InitHooks */
  • CJSON_PUBLIC(void *) cJSON_malloc(size_t size);
  • CJSON_PUBLIC(void) cJSON_free(void *object);
CJSON数据结构

CJSON核心数据结构就只有一个:

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

可以看出,json是一个嵌套数据结构,这与json的定义所表达的思想一致。

CJSON使用实例
  • /**
  • * @file simple-cjson.c
  • * @author your name (you@domain.com)
  • * @brief
  • * @version 0.1
  • * @date 2023-02-19
  • *
  • * @copyright Copyright (c) 2023
  • *
  • */
  • #include "../cJSON.h"
  • #include <stdio.h>
  • char simple_json[] = "{\
  • \"FirstName\": \"John\",\
  • \"LastName\": \"Doe\",\
  • \"Age\": 43,\
  • \"Address\": {\
  • \"Street\": \"Downing Street 10\",\
  • \"City\": \"London\",\
  • \"Country\": \"Great Britain\"\
  • },\
  • \"Phone numbers\": [\
  • \"+44 1234567\",\
  • \"+44 2345678\"\
  • ]\
  • }";
  • int main()
  • {
  • cJSON* json = cJSON_Parse(simple_json);
  • cJSON_AddStringToObject(json, "ID", "666");
  • char* print_json_str = cJSON_Print(json);
  • printf("simple json: %s", print_json_str);
  • return 0;
  • }

编译运行:

  • $./simple-cjson
  • simple json: {
  • "FirstName": "John",
  • "LastName": "Doe",
  • "Age": 43,
  • "Address": {
  • "Street": "Downing Street 10",
  • "City": "London",
  • "Country": "Great Britain"
  • },
  • "Phone numbers": ["+44 1234567", "+44 2345678"],
  • "ID": "666"
  • }

这部分完全可以参考CJSON项目的README

注意事项

CJSON使用ANSI C编写的,具有很多的指针操作,如果不注意非常容易产生指针操作相关的问题,这点最好阅读下项目的README和源代码。

城东书院 www.cdsy.xyz
方便获取更多学习、工作、生活信息请关注本站微信公众号城东书院 微信服务号城东书院 微信订阅号
推荐内容
相关内容
栏目更新
栏目热门
本栏推荐