cJSON的源码解读

前言

本博客内容主要是简单介绍一下cJSON的一些函数说明,由于源码不是很难,可以自己去看,如果嫌麻烦,可以直接看一下我的函数说明,然后大致看一下源码即可.

一定要去看源码,能需要很多;

cJSON的一些信息

这个地址可以下载到最新的源码: https://github.com/DaveGamble/cJSON

我看的源码比较老,学习为主,后期会阅读最新的源码;

以下是我看的源码部分:

链接：https://pan.baidu.com/s/1b7d4xsITPkUOCKbSDBsAmA 提取码：ame0

cJSON的数据结构

cJSON数据结构:
/* 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;

内存申请:
typedef struct cJSON_Hooks {
      void *(*malloc_fn)(size_t sz);
      void (*free_fn)(void *ptr);
} cJSON_Hooks;

基本函数

cJSON的基本函数:
	• cJSON_strcasecmp —— 两个字符比较是否相同，相同返回0，否则为1
	* cJSON_strdup —— 申请一块内存,用来保存其内容;

内部静态函数

cJSON内部函数:
	• cJSON_New_Item  —— 申请一块cJSON结构体大小的内存,并初始化为0
	• parse_number —— 将字符串转换为整型数据int或者double; 此函数分别对正负/0/数字/小数点/指数进行判断（注意，这些处理是有顺序，还有这里的代码还是值得参考的），最后将值赋给形参，并赋予类型；
	• Pow2gt —— 返回比x大的最小的2的N次方数；具体算法可参看以下文章：https://blog.csdn.net/dlf1769/article/details/78918045?utm_medium=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-1.nonecase&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-1.nonecase
	• ensure —— 确保读取的大小在字符串的范围内; 如果需要的大小在总长度内,直接范围偏移地址;如果不够,则使用Pow2gt先申请更大的一块,复制内容后,释放原来的内存,再返回偏移值;
	• print_number  —— 根据值的大小,将整型值改为字符串格式;分别有0,21位int和64位double数据
	• parse_hex4  —— 字符串转hex格式
	• parse_string  —— 申请指定大小的内存,将带转义字符格式的字符串和t这类的转换为字符串,赋值给cJSON结构的string类型,并判断其类型.(这里有utf16 -> utf8的转换过程,可以学习一下)
	• print_string_ptr  —— 将格式转换为纯字符串格式; 先判断是否有"和或者t这类的,如果没有,直接申请和拷贝数据后,添加2字节数据,返回申请的地址; 如果字符串为空,直接返回"";再获取长度后,添加指定的t这类结构加入字符串
	• parse_value  —— 不同格式产生不同的数据和类型;
	• parse_array —— 确定array类型,新申请cJSON结构体,child指针指向; 获取值,如果还是array,则进行递归;如果是",",则再进行child的操作;
	• parse_object —— 基本操作于array一致
	• print_object  —— 将cJSON对象转换为字符串格式
	• print_array —— 将cJSON对象转换为字符串格式
print_value   —— 将cJSON对象转换为字符串格式

对外函数

cJSON对外接口函数:
	• cJSON_InitHooks  —— 初始化内存申请的函数为malloc和free,如果形参时有效的,则使用形参的内存申请函数(用于调用用户自己的malloc实现)
	• cJSON_Delete —— 删除所有申请的内存!这个函数采用的是递归删除,先递归到每一个child对象,然后释放string_value和string的内存,如此,一个child的子对象的内存释放递归结束,再一次进行释放;
	• cJSON_ParseWithOpts —— 申请一个cJSON对象,再赋值;
	• cJSON_Parse——cJSON_ParseWithOpts(value, 0, 0)
cJSON_Print/cJSON_PrintUnformatted —— print_value(item,0,1/0,0)

以下是简单的处理以下的对外函数就不写了,一看就能懂:
/* Get Array size/item / object item. */
int    cJSON_GetArraySize(cJSON *array)                         {cJSON *c=array->child;int i=0;while(c)i++,c=c->next;return i;}
cJSON *cJSON_GetArrayItem(cJSON *array,int item)                {cJSON *c=array->child;  while (c && item>0) item--,c=c->next; return c;}
cJSON *cJSON_GetObjectItem(cJSON *object,const char *string)    {cJSON *c=object->child; while (c && cJSON_strcasecmp(c->string,string)) c=c->next; return c;}
/* Utility for array list handling. */
static void suffix_object(cJSON *prev,cJSON *item) {prev->next=item;item->prev=prev;}
/* Utility for handling references. */
static cJSON *create_reference(cJSON *item) {cJSON *ref=cJSON_New_Item();if (!ref) return 0;memcpy(ref,item,sizeof(cJSON));ref->string=0;ref->type|=cJSON_IsReference;ref->next=ref->prev=0;return ref;}
/* Add item to array/object. */
void   cJSON_AddItemToArray(cJSON *array, cJSON *item)                      {cJSON *c=array->child;if (!item) return; if (!c) {array->child=item;} else {while (c && c->next) c=c->next; suffix_object(c,item);}}
void   cJSON_AddItemToObject(cJSON *object,const char *string,cJSON *item)  {if (!item) return; if (item->string) cJSON_free(item->string);item->string=cJSON_strdup(string);cJSON_AddItemToArray(object,item);}
void   cJSON_AddItemToObjectCS(cJSON *object,const char *string,cJSON *item)    {if (!item) return; if (!(item->type&cJSON_StringIsConst) && item->string) cJSON_free(item->string);item->string=(char*)string;item->type|=cJSON_StringIsConst;cJSON_AddItemToArray(object,item);}
void    cJSON_AddItemReferenceToArray(cJSON *array, cJSON *item)                        {cJSON_AddItemToArray(array,create_reference(item));}
void    cJSON_AddItemReferenceToObject(cJSON *object,const char *string,cJSON *item)    {cJSON_AddItemToObject(object,string,create_reference(item));}
cJSON *cJSON_DetachItemFromArray(cJSON *array,int which)            {cJSON *c=array->child;while (c && which>0) c=c->next,which--;if (!c) return 0;
    if (c->prev) c->prev->next=c->next;if (c->next) c->next->prev=c->prev;if (c==array->child) array->child=c->next;c->prev=c->next=0;return c;}
void   cJSON_DeleteItemFromArray(cJSON *array,int which)            {cJSON_Delete(cJSON_DetachItemFromArray(array,which));}
cJSON *cJSON_DetachItemFromObject(cJSON *object,const char *string) {int i=0;cJSON *c=object->child;while (c && cJSON_strcasecmp(c->string,string)) i++,c=c->next;if (c) return cJSON_DetachItemFromArray(object,i);return 0;}
void   cJSON_DeleteItemFromObject(cJSON *object,const char *string) {cJSON_Delete(cJSON_DetachItemFromObject(object,string));}
/* Replace array/object items with new ones. */
void   cJSON_InsertItemInArray(cJSON *array,int which,cJSON *newitem)       {cJSON *c=array->child;while (c && which>0) c=c->next,which--;if (!c) {cJSON_AddItemToArray(array,newitem);return;}
    newitem->next=c;newitem->prev=c->prev;c->prev=newitem;if (c==array->child) array->child=newitem; else newitem->prev->next=newitem;}
void   cJSON_ReplaceItemInArray(cJSON *array,int which,cJSON *newitem)      {cJSON *c=array->child;while (c && which>0) c=c->next,which--;if (!c) return;
    newitem->next=c->next;newitem->prev=c->prev;if (newitem->next) newitem->next->prev=newitem;
    if (c==array->child) array->child=newitem; else newitem->prev->next=newitem;c->next=c->prev=0;cJSON_Delete(c);}
void   cJSON_ReplaceItemInObject(cJSON *object,const char *string,cJSON *newitem){int i=0;cJSON *c=object->child;while(c && cJSON_strcasecmp(c->string,string))i++,c=c->next;if(c){newitem->string=cJSON_strdup(string);cJSON_ReplaceItemInArray(object,i,newitem);}}
/* Create basic types: */
cJSON *cJSON_CreateNull(void)                   {cJSON *item=cJSON_New_Item();if(item)item->type=cJSON_NULL;return item;}
cJSON *cJSON_CreateTrue(void)                   {cJSON *item=cJSON_New_Item();if(item)item->type=cJSON_True;return item;}
cJSON *cJSON_CreateFalse(void)                  {cJSON *item=cJSON_New_Item();if(item)item->type=cJSON_False;return item;}
cJSON *cJSON_CreateBool(int b)                  {cJSON *item=cJSON_New_Item();if(item)item->type=b?cJSON_True:cJSON_False;return item;}
cJSON *cJSON_CreateNumber(double num)           {cJSON *item=cJSON_New_Item();if(item){item->type=cJSON_Number;item->valuedouble=num;item->valueint=(int)num;}return item;}
cJSON *cJSON_CreateString(const char *string)   {cJSON *item=cJSON_New_Item();if(item){item->type=cJSON_String;item->valuestring=cJSON_strdup(string);}return item;}
cJSON *cJSON_CreateArray(void)                  {cJSON *item=cJSON_New_Item();if(item)item->type=cJSON_Array;return item;}
cJSON *cJSON_CreateObject(void)                 {cJSON *item=cJSON_New_Item();if(item)item->type=cJSON_Object;return item;}
/* Create Arrays: */
cJSON *cJSON_CreateIntArray(const int *numbers,int count)       {int i;cJSON *n=0,*p=0,*a=cJSON_CreateArray();for(i=0;a && i<count;i++){n=cJSON_CreateNumber(numbers[i]);if(!i)a->child=n;else suffix_object(p,n);p=n;}return a;}
cJSON *cJSON_CreateFloatArray(const float *numbers,int count)   {int i;cJSON *n=0,*p=0,*a=cJSON_CreateArray();for(i=0;a && i<count;i++){n=cJSON_CreateNumber(numbers[i]);if(!i)a->child=n;else suffix_object(p,n);p=n;}return a;}
cJSON *cJSON_CreateDoubleArray(const double *numbers,int count) {int i;cJSON *n=0,*p=0,*a=cJSON_CreateArray();for(i=0;a && i<count;i++){n=cJSON_CreateNumber(numbers[i]);if(!i)a->child=n;else suffix_object(p,n);p=n;}return a;}
cJSON *cJSON_CreateStringArray(const char **strings,int count)  {int i;cJSON *n=0,*p=0,*a=cJSON_CreateArray();for(i=0;a && i<count;i++){n=cJSON_CreateString(strings[i]);if(!i)a->child=n;else suffix_object(p,n);p=n;}return a;}

使用

可以从test文件里得知使用方法:

/*
  Copyright (c) 2009 Dave Gamble
 
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
 
  The above copyright notice and this permission notice shall be included in
  all copies or substantial portions of the Software.
 
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  THE SOFTWARE.
*/

#include <stdio.h>
#include <stdlib.h>
#include "cJSON.h"

/* Parse text to JSON, then render back to text, and print! */
void doit(char *text)
{
	char *out;cJSON *json;
	
	json=cJSON_Parse(text);
	if (!json) {printf("Error before: [%s]n",cJSON_GetErrorPtr());}
	else
	{
		out=cJSON_Print(json);
		cJSON_Delete(json);
		printf("%sn",out);
		free(out);
	}
}

/* Read a file, parse, render back, etc. */
void dofile(char *filename)
{
	FILE *f;long len;char *data;
	
	f=fopen(filename,"rb");fseek(f,0,SEEK_END);len=ftell(f);fseek(f,0,SEEK_SET);
	data=(char*)malloc(len+1);fread(data,1,len,f);fclose(f);
	doit(data);
	free(data);
}

/* Used by some code below as an example datatype. */
struct record {const char *precision;double lat,lon;const char *address,*city,*state,*zip,*country; };

/* Create a bunch of objects as demonstration. */
void create_objects()
{
	cJSON *root,*fmt,*img,*thm,*fld;char *out;int i;	/* declare a few. */
	/* Our "days of the week" array: */
	const char *strings[7]={"Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"};
	/* Our matrix: */
	int numbers[3][3]={{0,-1,0},{1,0,0},{0,0,1}};
	/* Our "gallery" item: */
	int ids[4]={116,943,234,38793};
	/* Our array of "records": */
	struct record fields[2]={
		{"zip",37.7668,-1.223959e+2,"","SAN FRANCISCO","CA","94107","US"},
		{"zip",37.371991,-1.22026e+2,"","SUNNYVALE","CA","94085","US"}};

	/* Here we construct some JSON standards, from the JSON site. */
	
	/* Our "Video" datatype: */
	root=cJSON_CreateObject();	
	cJSON_AddItemToObject(root, "name", cJSON_CreateString("Jack ("Bee") Nimble"));
	cJSON_AddItemToObject(root, "format", fmt=cJSON_CreateObject());
	cJSON_AddStringToObject(fmt,"type",		"rect");
	cJSON_AddNumberToObject(fmt,"width",		1920);
	cJSON_AddNumberToObject(fmt,"height",		1080);
	cJSON_AddFalseToObject (fmt,"interlace");
	cJSON_AddNumberToObject(fmt,"frame rate",	24);
	
	out=cJSON_Print(root);	cJSON_Delete(root);	printf("%sn",out);	free(out);	/* Print to text, Delete the cJSON, print it, release the string. */

	/* Our "days of the week" array: */
	root=cJSON_CreateStringArray(strings,7);

	out=cJSON_Print(root);	cJSON_Delete(root);	printf("%sn",out);	free(out);

	/* Our matrix: */
	root=cJSON_CreateArray();
	for (i=0;i<3;i++) cJSON_AddItemToArray(root,cJSON_CreateIntArray(numbers[i],3));

/*	cJSON_ReplaceItemInArray(root,1,cJSON_CreateString("Replacement")); */
	
	out=cJSON_Print(root);	cJSON_Delete(root);	printf("%sn",out);	free(out);


	/* Our "gallery" item: */
	root=cJSON_CreateObject();
	cJSON_AddItemToObject(root, "Image", img=cJSON_CreateObject());
	cJSON_AddNumberToObject(img,"Width",800);
	cJSON_AddNumberToObject(img,"Height",600);
	cJSON_AddStringToObject(img,"Title","View from 15th Floor");
	cJSON_AddItemToObject(img, "Thumbnail", thm=cJSON_CreateObject());
	cJSON_AddStringToObject(thm, "Url", "http:/*www.example.com/image/481989943");
	cJSON_AddNumberToObject(thm,"Height",125);
	cJSON_AddStringToObject(thm,"Width","100");
	cJSON_AddItemToObject(img,"IDs", cJSON_CreateIntArray(ids,4));

	out=cJSON_Print(root);	cJSON_Delete(root);	printf("%sn",out);	free(out);

	/* Our array of "records": */

	root=cJSON_CreateArray();
	for (i=0;i<2;i++)
	{
		cJSON_AddItemToArray(root,fld=cJSON_CreateObject());
		cJSON_AddStringToObject(fld, "precision", fields[i].precision);
		cJSON_AddNumberToObject(fld, "Latitude", fields[i].lat);
		cJSON_AddNumberToObject(fld, "Longitude", fields[i].lon);
		cJSON_AddStringToObject(fld, "Address", fields[i].address);
		cJSON_AddStringToObject(fld, "City", fields[i].city);
		cJSON_AddStringToObject(fld, "State", fields[i].state);
		cJSON_AddStringToObject(fld, "Zip", fields[i].zip);
		cJSON_AddStringToObject(fld, "Country", fields[i].country);
	}
	
/*	cJSON_ReplaceItemInObject(cJSON_GetArrayItem(root,1),"City",cJSON_CreateIntArray(ids,4)); */
	
	out=cJSON_Print(root);	cJSON_Delete(root);	printf("%sn",out);	free(out);

}

int main (int argc, const char * argv[]) {
	/* a bunch of json: */
	char text1[]="{n"name": "Jack (\"Bee\") Nimble", n"format": {"type":       "rect", n"width":      1920, n"height":     1080, n"interlace":  false,"frame rate": 24n}n}";	
	char text2[]="["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"]";
	char text3[]="[n    [0, -1, 0],n    [1, 0, 0],n    [0, 0, 1]n	]n";
	char text4[]="{n		"Image": {n			"Width":  800,n			"Height": 600,n			"Title":  "View from 15th Floor",n			"Thumbnail": {n				"Url":    "http:/*www.example.com/image/481989943",n				"Height": 125,n				"Width":  "100"n			},n			"IDs": [116, 943, 234, 38793]n		}n	}";
	char text5[]="[n	 {n	 "precision": "zip",n	 "Latitude":  37.7668,n	 "Longitude": -122.3959,n	 "Address":   "",n	 "City":      "SAN FRANCISCO",n	 "State":     "CA",n	 "Zip":       "94107",n	 "Country":   "US"n	 },n	 {n	 "precision": "zip",n	 "Latitude":  37.371991,n	 "Longitude": -122.026020,n	 "Address":   "",n	 "City":      "SUNNYVALE",n	 "State":     "CA",n	 "Zip":       "94085",n	 "Country":   "US"n	 }n	 ]";

	/* Process each json textblock by parsing, then rebuilding: */
	doit(text1);
	doit(text2);	
	doit(text3);
	doit(text4);
	doit(text5);

	/* Parse standard testfiles: */
/*	dofile("../../tests/test1"); */
/*	dofile("../../tests/test2"); */
/*	dofile("../../tests/test3"); */
/*	dofile("../../tests/test4"); */
/*	dofile("../../tests/test5"); */

	/* Now some samplecode for building objects concisely: */
	create_objects();
	
	return 0;
}

收获

简单说说我在这个源码里的收获吧:

1. 了解了utf-16的格式;
2. 一种获取到某个值最接近的2的n次的值算法;

最后

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