cJSON源碼解析（超級詳細！！！）

一、JSON數據表示

JSON(JavaScript Object Notation(JavaScript 對象表示法))，是存儲和交換文本信息的語法，類似 XML，但JSON 比 XML 更小、更快，更易解析。

{
    "sites": [
    { "name":"菜鳥教程" , "url":"www.runoob.com" }, 
    { "name":"google" , "url":"www.google.com" }, 
    { "name":"微博" , "url":"www.weibo.com" }
    ]
}

大括號保存對象，中括號保存數組，鍵值對以":"分隔，其中鍵只能是字符串，值可以是數字（整數或浮點數）、字符串、邏輯值（true 或 false）、數組、對象或null，不同的鍵值對之間以","分隔。

二、CJSON數據結構和函數

cJSON是一個C語言編寫的JSON格式數據解析器，他把JSON數據看成是層次樹，同級之間用雙向鏈表相連，上下級用指針形成樹形結構。

1.cJSON結構體定義

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;

成員變量type包括cJSON_Object、cJSON_Array、cJSON_Number、cJSON_String、cJSON_True、cJSON_False、cJSON_NULL。

成員變量valuestring表示type爲cJSON_String時string的值，valueint表示type爲cJSON_Number時int的值，或是double被截斷爲int的值，valuedouble表示type爲cJSON_Number時double的值。

成員變量string表示cJSON節點的名稱。

2.創建空節點

static cJSON *cJSON_New_Item(void)
{
	cJSON* node = (cJSON*)cJSON_malloc(sizeof(cJSON));
	if (node) memset(node,0,sizeof(cJSON));
	return node;
}

3.創建相應type節點

都是先創建一個空節點，然後設置type，有的節點還需要給相應的value賦值。

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;}

4.創建節點數組

根據普通數組創建不同類型指定大小的cJSON數組，所謂數組即存放的是相同類型的數據。 

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;//數組節點的孩子節點是數組第一個元素
        else suffix_object(p,n);
        //static void suffix_object(cJSON *prev,cJSON *item) {prev->next=item;item->prev=prev;}
        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;
}

5.添加孩子節點到Array，Object上

添加孩子節點都是調用cJSON_AddItemToObject函數。

#define cJSON_AddNullToObject(object,name)	cJSON_AddItemToObject(object, name, cJSON_CreateNull())
#define cJSON_AddTrueToObject(object,name)	cJSON_AddItemToObject(object, name, cJSON_CreateTrue())
#define cJSON_AddFalseToObject(object,name)	cJSON_AddItemToObject(object, name, cJSON_CreateFalse())
#define cJSON_AddBoolToObject(object,name,b)    cJSON_AddItemToObject(object, name, cJSON_CreateBool(b))
#define cJSON_AddNumberToObject(object,name,n)	cJSON_AddItemToObject(object, name, cJSON_CreateNumber(n))
#define cJSON_AddStringToObject(object,name,s)	cJSON_AddItemToObject(object, name, cJSON_CreateString(s))

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);//將item添加到object數組上
}
void cJSON_AddItemToArray(cJSON *array, cJSON *item){
    cJSON *c=array->child;
    if (!item) return; 
    if (!c) {array->child=item;}//如果array沒有孩子，item是其第一個孩子
    else {
        while (c && c->next) c=c->next; //如果array有孩子，將item插入到數組末尾
//static void suffix_object(cJSON *prev,cJSON *item) {prev->next=item;item->prev=prev;}
        suffix_object(c,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);
}

6.創建引用節點

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;
}

7.添加引用節點到Array，Object上

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));
}

8.獲取Array、Object

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;
}

9.插入/替換節點

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);
    }
}

10.刪除孩子節點

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));
}

11.解析層次樹

cJSON *cJSON_Parse(const char *value) {return cJSON_ParseWithOpts(value,0,0);}

cJSON *cJSON_ParseWithOpts(const char *value,const char **return_parse_end,int require_null_terminated)
{
	const char *end=0;
	cJSON *c=cJSON_New_Item();
	ep=0;
	if (!c) return 0;       /* memory fail */

	end=parse_value(c,skip(value));//skip去除value前面的控制字符（asc值小於33）
	if (!end)	{cJSON_Delete(c);return 0;}	/* parse failure. ep is set. */

	/* if we require null-terminated JSON without appended garbage, skip and then check for a null terminator */
	if (require_null_terminated) {end=skip(end);if (*end) {cJSON_Delete(c);ep=end;return 0;}}
	if (return_parse_end) *return_parse_end=end;
	return c;
}

static const char *parse_value(cJSON *item,const char *value)
{
	if (!value)						return 0;	/* Fail on null. */
	if (!strncmp(value,"null",4))	{ item->type=cJSON_NULL;  return value+4; }
	if (!strncmp(value,"false",5))	{ item->type=cJSON_False; return value+5; }
	if (!strncmp(value,"true",4))	{ item->type=cJSON_True; item->valueint=1;	return value+4; }
	if (*value=='\"')				{ return parse_string(item,value); }
	if (*value=='-' || (*value>='0' && *value<='9'))	{ return parse_number(item,value); }
	if (*value=='[')				{ return (item,value); }
	if (*value=='{')				{ return parse_object(item,value); }

	ep=value;return 0;	/* failure. */
}

解析函數的第一個參數都是空節點，用於解析後填充信息，第二個參數是之前解析剩餘的字符串，所有的\n\r會被過濾掉。

static const char *parse_string(cJSON *item,const char *str)
{
	const char *ptr=str+1;char *ptr2;char *out;int len=0;unsigned uc,uc2;
	if (*str!='\"') {ep=str;return 0;}	/* not a string! *///c語言中\"是一個字符
	//ptr沒有到字符串末尾，len記錄string的長度
	while (*ptr!='\"' && *ptr && ++len) if (*ptr++ == '\\') ptr++;	/* Skip escaped quotes. 轉義字符*/
	
	out=(char*)cJSON_malloc(len+1);	/* This is how long we need for the string, roughly. */
	if (!out) return 0;
	
	ptr=str+1;ptr2=out;
	while (*ptr!='\"' && *ptr)
	{
		if (*ptr!='\\') *ptr2++=*ptr++;//進行string賦值
		else
		{
			ptr++;
			switch (*ptr)
			{
				case 'b': *ptr2++='\b';	break;
				case 'f': *ptr2++='\f';	break;
				case 'n': *ptr2++='\n';	break;
				case 'r': *ptr2++='\r';	break;
				case 't': *ptr2++='\t';	break;
				case 'u':	 /* transcode utf16 to utf8. */
					uc=parse_hex4(ptr+1);ptr+=4;	/* get the unicode char. */

					if ((uc>=0xDC00 && uc<=0xDFFF) || uc==0)	break;	/* check for invalid.	*/

					if (uc>=0xD800 && uc<=0xDBFF)	/* UTF16 surrogate pairs.	*/
					{
						if (ptr[1]!='\\' || ptr[2]!='u')	break;	/* missing second-half of surrogate.	*/
						uc2=parse_hex4(ptr+3);ptr+=6;
						if (uc2<0xDC00 || uc2>0xDFFF)		break;	/* invalid second-half of surrogate.	*/
						uc=0x10000 + (((uc&0x3FF)<<10) | (uc2&0x3FF));
					}

					len=4;if (uc<0x80) len=1;else if (uc<0x800) len=2;else if (uc<0x10000) len=3; ptr2+=len;
					
					switch (len) {
						case 4: *--ptr2 =((uc | 0x80) & 0xBF); uc >>= 6;
						case 3: *--ptr2 =((uc | 0x80) & 0xBF); uc >>= 6;
						case 2: *--ptr2 =((uc | 0x80) & 0xBF); uc >>= 6;
						case 1: *--ptr2 =(uc | firstByteMark[len]);
					}
					ptr2+=len;
					break;
				default:  *ptr2++=*ptr; break;
			}
			ptr++;
		}
	}
	*ptr2=0;
	if (*ptr=='\"') ptr++;
	item->valuestring=out;
	item->type=cJSON_String;
	return ptr;
}

static const char *parse_number(cJSON *item,const char *num)
{
	double n=0,sign=1,scale=0;int subscale=0,signsubscale=1;

	if (*num=='-') sign=-1,num++;	/* Has sign? */
	if (*num=='0') num++;			/* is zero */
	if (*num>='1' && *num<='9')	do	n=(n*10.0)+(*num++ -'0');	while (*num>='0' && *num<='9');	/* Number? */
	if (*num=='.' && num[1]>='0' && num[1]<='9') {num++;		do	n=(n*10.0)+(*num++ -'0'),scale--; while (*num>='0' && *num<='9');}	/* Fractional part? */
	if (*num=='e' || *num=='E')		/* Exponent? */
	{	num++;if (*num=='+') num++;	else if (*num=='-') signsubscale=-1,num++;		/* With sign? */
		while (*num>='0' && *num<='9') subscale=(subscale*10)+(*num++ - '0');	/* Number? */
	}

	n=sign*n*pow(10.0,(scale+subscale*signsubscale));	/* number = +/- number.fraction * 10^+/- exponent */
	
	item->valuedouble=n;
	item->valueint=(int)n;
	item->type=cJSON_Number;
	return num;
}

static const char *parse_array(cJSON *item,const char *value)
{
	cJSON *child;
	if (*value!='[')	{ep=value;return 0;}	/* not an array! */

	item->type=cJSON_Array;
	value=skip(value+1);
	if (*value==']') return value+1;	/* empty array. */

	item->child=child=cJSON_New_Item();
	if (!item->child) return 0;		 /* memory fail */
	value=skip(parse_value(child,skip(value)));	/* skip any spacing, get the value. */
	if (!value) return 0;

	while (*value==',')
	{
		cJSON *new_item;
		if (!(new_item=cJSON_New_Item())) return 0; 	/* memory fail */
		child->next=new_item;new_item->prev=child;child=new_item;
		value=skip(parse_value(child,skip(value+1)));
		if (!value) return 0;	/* memory fail */
	}

	if (*value==']') return value+1;	/* end of array */
	ep=value;return 0;	/* malformed. */
}

static const char *parse_object(cJSON *item,const char *value)
{
	cJSON *child;
	if (*value!='{')	{ep=value;return 0;}	/* not an object! */
	
	item->type=cJSON_Object;
	value=skip(value+1);
	if (*value=='}') return value+1;	/* empty array. */
	//非空Object肯定有孩子節點，創建一個空節點作爲孩子節點
	item->child=child=cJSON_New_Item();
	if (!item->child) return 0;
	value=skip(parse_string(child,skip(value)));//Object的key肯定是string，所以緊接着是解析string
	if (!value) return 0;
    //第一次解析得到的valuestring作爲節點名稱，並且重置valuestring
	child->string=child->valuestring;child->valuestring=0;
	if (*value!=':') {ep=value;return 0;}	/* fail! */
    //值可以是很多類型，所以這裏又調用parse_value
	value=skip(parse_value(child,skip(value+1)));	/* skip any spacing, get the value. */
    //第二次解析到的child就沒有執行置換valuestring的操作，因爲：後面的是值，不需要置換
	if (!value) return 0;
	//，說明之後的內容都屬於同一個Object，並且是同一級別
	while (*value==',')
	{
		cJSON *new_item;
		if (!(new_item=cJSON_New_Item()))	return 0; /* memory fail */
		child->next=new_item;new_item->prev=child;child=new_item;
		value=skip(parse_string(child,skip(value+1)));
		if (!value) return 0;
        //第一次解析得到的valuestring作爲節點名稱，並且重置valuestring
		child->string=child->valuestring;child->valuestring=0;
		if (*value!=':') {ep=value;return 0;}	/* fail! */
		value=skip(parse_value(child,skip(value+1)));	/* skip any spacing, get the value. */
		if (!value) return 0;
	}
	
	if (*value=='}') return value+1;	/* end of array */
	ep=value;return 0;	/* malformed. */
}

12.打印層次樹

將解析後的JSON格式數據再還原成JSON格式數據打印。

char *cJSON_Print(cJSON *item)		 {return print_value(item,0,1,0);}
char *cJSON_PrintUnformatted(cJSON *item){return print_value(item,0,0,0);}
char *cJSON_PrintBuffered(cJSON *item,int prebuffer,int fmt)
{
	printbuffer p;
	p.buffer=(char*)cJSON_malloc(prebuffer);
	p.length=prebuffer;
	p.offset=0;
	return print_value(item,0,fmt,&p);
	return p.buffer;
}
static char *print_value(cJSON *item,int depth,int fmt,printbuffer *p)
{
	char *out=0;
	if (!item) return 0;
	if (p)
	{
		switch ((item->type)&255)
		{
			case cJSON_NULL:	{out=ensure(p,5);	if (out) strcpy(out,"null");	break;}
			case cJSON_False:	{out=ensure(p,6);	if (out) strcpy(out,"false");	break;}
			case cJSON_True:	{out=ensure(p,5);	if (out) strcpy(out,"true");	break;}
			case cJSON_Number:	out=print_number(item,p);break;
			case cJSON_String:	out=print_string(item,p);break;
			case cJSON_Array:	out=print_array(item,depth,fmt,p);break;
			case cJSON_Object:	out=print_object(item,depth,fmt,p);break;
		}
	}
	else
	{
		switch ((item->type)&255)//不同的值類型對應不同的編號
		{
			case cJSON_NULL:	out=cJSON_strdup("null");	break;
			case cJSON_False:	out=cJSON_strdup("false");break;
			case cJSON_True:	out=cJSON_strdup("true"); break;
			case cJSON_Number:	out=print_number(item,0);break;
			case cJSON_String:	out=print_string(item,0);break;
			case cJSON_Array:	out=print_array(item,depth,fmt,0);break;
			case cJSON_Object:	out=print_object(item,depth,fmt,0);break;
		}
	}
	return out;
}

static char *print_number(cJSON *item,printbuffer *p)
{
	char *str=0;
	double d=item->valuedouble;
	if (d==0)
	{
		if (p)	str=ensure(p,2);
		else	str=(char*)cJSON_malloc(2);	/* special case for 0. */
		if (str) strcpy(str,"0");
	}
	else if (fabs(((double)item->valueint)-d)<=DBL_EPSILON && d<=INT_MAX && d>=INT_MIN)
	{
		if (p)	str=ensure(p,21);
		else	str=(char*)cJSON_malloc(21);	/* 2^64+1 can be represented in 21 chars. */
		if (str)	sprintf(str,"%d",item->valueint);
	}
	else
	{
		if (p)	str=ensure(p,64);
		else	str=(char*)cJSON_malloc(64);	/* This is a nice tradeoff. */
		if (str)
		{
			if (fabs(floor(d)-d)<=DBL_EPSILON && fabs(d)<1.0e60)sprintf(str,"%.0f",d);
			else if (fabs(d)<1.0e-6 || fabs(d)>1.0e9)			sprintf(str,"%e",d);
			else												sprintf(str,"%f",d);
		}
	}
	return str;
}

static char *print_string_ptr(const char *str,printbuffer *p)
{
	const char *ptr;char *ptr2,*out;int len=0,flag=0;unsigned char token;
	//ptr移至str後
	for (ptr=str;*ptr;ptr++) flag|=((*ptr>0 && *ptr<32)||(*ptr=='\"')||(*ptr=='\\'))?1:0;
	if (!flag)
	{
		len=ptr-str;
		if (p) out=ensure(p,len+3);
		else		out=(char*)cJSON_malloc(len+3);
		if (!out) return 0;
		ptr2=out;*ptr2++='\"';//ptr2的位置賦值\"，之後指針++
		strcpy(ptr2,str);
		ptr2[len]='\"';
		ptr2[len+1]=0;//將字符串構造成\"string\"
		return out;
	}
	
	if (!str)
	{
		if (p)	out=ensure(p,3);
		else	out=(char*)cJSON_malloc(3);
		if (!out) return 0;
		strcpy(out,"\"\"");
		return out;
	}
	ptr=str;while ((token=*ptr) && ++len) {if (strchr("\"\\\b\f\n\r\t",token)) len++; else if (token<32) len+=5;ptr++;}
	
	if (p)	out=ensure(p,len+3);
	else	out=(char*)cJSON_malloc(len+3);
	if (!out) return 0;

	ptr2=out;ptr=str;
	*ptr2++='\"';
	while (*ptr)
	{
		if ((unsigned char)*ptr>31 && *ptr!='\"' && *ptr!='\\') *ptr2++=*ptr++;
		else
		{
			*ptr2++='\\';
			switch (token=*ptr++)
			{
				case '\\':	*ptr2++='\\';	break;
				case '\"':	*ptr2++='\"';	break;
				case '\b':	*ptr2++='b';	break;
				case '\f':	*ptr2++='f';	break;
				case '\n':	*ptr2++='n';	break;
				case '\r':	*ptr2++='r';	break;
				case '\t':	*ptr2++='t';	break;
				default: sprintf(ptr2,"u%04x",token);ptr2+=5;	break;	/* escape and print */
			}
		}
	}
	*ptr2++='\"';*ptr2++=0;
	return out;
}
/* Invote print_string_ptr (which is useful) on an item. */
static char *print_string(cJSON *item,printbuffer *p)	{return print_string_ptr(item->valuestring,p);}

static char *print_array(cJSON *item,int depth,int fmt,printbuffer *p)
{
	char **entries;
	char *out=0,*ptr,*ret;int len=5;
	cJSON *child=item->child;
	int numentries=0,i=0,fail=0;
	size_t tmplen=0;
	
	/* How many entries in the array? */
	while (child) numentries++,child=child->next;
	/* Explicitly handle numentries==0 */
	if (!numentries)
	{
		if (p)	out=ensure(p,3);
		else	out=(char*)cJSON_malloc(3);
		if (out) strcpy(out,"[]");
		return out;
	}

	if (p)
	{
		/* Compose the output array. */
		i=p->offset;
		ptr=ensure(p,1);if (!ptr) return 0;	*ptr='[';	p->offset++;
		child=item->child;
		while (child && !fail)
		{
			print_value(child,depth+1,fmt,p);
			p->offset=update(p);
			if (child->next) {len=fmt?2:1;ptr=ensure(p,len+1);if (!ptr) return 0;*ptr++=',';if(fmt)*ptr++=' ';*ptr=0;p->offset+=len;}
			child=child->next;
		}
		ptr=ensure(p,2);if (!ptr) return 0;	*ptr++=']';*ptr=0;
		out=(p->buffer)+i;
	}
	else
	{
		/* Allocate an array to hold the values for each */
		entries=(char**)cJSON_malloc(numentries*sizeof(char*));
		if (!entries) return 0;
		memset(entries,0,numentries*sizeof(char*));
		/* Retrieve all the results: */
		child=item->child;
		while (child && !fail)
		{
			ret=print_value(child,depth+1,fmt,0);
			entries[i++]=ret;
			if (ret) len+=strlen(ret)+2+(fmt?1:0); else fail=1;
			child=child->next;
		}
		
		/* If we didn't fail, try to malloc the output string */
		if (!fail)	out=(char*)cJSON_malloc(len);
		/* If that fails, we fail. */
		if (!out) fail=1;

		/* Handle failure. */
		if (fail)
		{
			for (i=0;i<numentries;i++) if (entries[i]) cJSON_free(entries[i]);
			cJSON_free(entries);
			return 0;
		}
		
		/* Compose the output array. */
		*out='[';
		ptr=out+1;*ptr=0;
		for (i=0;i<numentries;i++)
		{
			tmplen=strlen(entries[i]);memcpy(ptr,entries[i],tmplen);ptr+=tmplen;
			if (i!=numentries-1) {*ptr++=',';if(fmt)*ptr++=' ';*ptr=0;}
			cJSON_free(entries[i]);
		}
		cJSON_free(entries);
		*ptr++=']';*ptr++=0;
	}
	return out;	
}

static char *print_object(cJSON *item,int depth,int fmt,printbuffer *p)
{
	char **entries=0,**names=0;
	char *out=0,*ptr,*ret,*str;int len=7,i=0,j;
	cJSON *child=item->child;
	int numentries=0,fail=0;
	size_t tmplen=0;
	//找到屬於該Object的同一級孩子
	while (child) numentries++,child=child->next;
	/* Explicitly handle empty object case */
	if (!numentries)
	{
		if (p) out=ensure(p,fmt?depth+4:3);
		else	out=(char*)cJSON_malloc(fmt?depth+4:3);
		if (!out)	return 0;
		ptr=out;*ptr++='{';
		if (fmt) {*ptr++='\n';for (i=0;i<depth-1;i++) *ptr++='\t';}
		*ptr++='}';*ptr++=0;
		return out;
	}
	if (p)
	{
		/* Compose the output: */
		i=p->offset;
		len=fmt?2:1;	ptr=ensure(p,len+1);	if (!ptr) return 0;
		*ptr++='{';	if (fmt) *ptr++='\n';	*ptr=0;	p->offset+=len;
		child=item->child;depth++;
		while (child)
		{
			if (fmt)
			{
				ptr=ensure(p,depth);	if (!ptr) return 0;
				for (j=0;j<depth;j++) *ptr++='\t';
				p->offset+=depth;
			}
			print_string_ptr(child->string,p);
			p->offset=update(p);
			
			len=fmt?2:1;
			ptr=ensure(p,len);	if (!ptr) return 0;
			*ptr++=':';if (fmt) *ptr++='\t';
			p->offset+=len;
			
			print_value(child,depth,fmt,p);
			p->offset=update(p);

			len=(fmt?1:0)+(child->next?1:0);
			ptr=ensure(p,len+1); if (!ptr) return 0;
			if (child->next) *ptr++=',';
			if (fmt) *ptr++='\n';*ptr=0;
			p->offset+=len;
			child=child->next;
		}
		ptr=ensure(p,fmt?(depth+1):2);	 if (!ptr) return 0;
		if (fmt)	for (i=0;i<depth-1;i++) *ptr++='\t';
		*ptr++='}';*ptr=0;
		out=(p->buffer)+i;
	}
	else
	{
		/* Allocate space for the names and the objects */
		entries=(char**)cJSON_malloc(numentries*sizeof(char*));
		if (!entries) return 0;
		names=(char**)cJSON_malloc(numentries*sizeof(char*));
		if (!names) {cJSON_free(entries);return 0;}
		memset(entries,0,sizeof(char*)*numentries);
		memset(names,0,sizeof(char*)*numentries);

		/* Collect all the results into our arrays: */
		child=item->child;depth++;if (fmt) len+=depth;
		while (child)
		{
            //打印key，值肯定是string，所以調用print_string_ptr
			names[i]=str=print_string_ptr(child->string,0);
            //打印value，value可以是多種類型，所以調用print_value，ret是復原爲解析之前的格式
			entries[i++]=ret=print_value(child,depth,fmt,0);
			if (str && ret) len+=strlen(ret)+strlen(str)+2+(fmt?2+depth:0); else fail=1;
			child=child->next;
		}
		
		/* Try to allocate the output string */
		if (!fail)	out=(char*)cJSON_malloc(len);
		if (!out) fail=1;

		/* Handle failure */
		if (fail)
		{
			for (i=0;i<numentries;i++) {if (names[i]) cJSON_free(names[i]);if (entries[i]) cJSON_free(entries[i]);}
			cJSON_free(names);cJSON_free(entries);
			return 0;
		}
		
		/* 重構輸出Compose the output: */
		*out='{';ptr=out+1;if (fmt)*ptr++='\n';*ptr=0;
		for (i=0;i<numentries;i++)
		{
			if (fmt) for (j=0;j<depth;j++) *ptr++='\t';
			tmplen=strlen(names[i]);memcpy(ptr,names[i],tmplen);ptr+=tmplen;
			*ptr++=':';if (fmt) *ptr++='\t';
			strcpy(ptr,entries[i]);ptr+=strlen(entries[i]);
			if (i!=numentries-1) *ptr++=',';
			if (fmt) *ptr++='\n';*ptr=0;
			cJSON_free(names[i]);cJSON_free(entries[i]);
		}
		
		cJSON_free(names);cJSON_free(entries);
		if (fmt) for (i=0;i<depth-1;i++) *ptr++='\t';
		*ptr++='}';*ptr++=0;
	}
	return out;	
}

13.刪除層次樹

刪除整個cJSON層次樹結構。

void cJSON_Delete(cJSON *c)
{
	cJSON *next;
	while (c)
	{
		next=c->next;
		if (!(c->type&cJSON_IsReference) && c->child) cJSON_Delete(c->child);
		if (!(c->type&cJSON_IsReference) && c->valuestring) cJSON_free(c->valuestring);
		if (!(c->type&cJSON_StringIsConst) && c->string) cJSON_free(c->string);
		cJSON_free(c);
		c=next;
	}
}

14.其他函數

//字符串比較函數（不區分大小寫），相同返回0，大於返回正值，小於返回負值
static int cJSON_strcasecmp(const char *s1,const char *s2)
{
	if (!s1) return (s1==s2)?0:1;if (!s2) return 1;
	for(; tolower(*s1) == tolower(*s2); ++s1, ++s2)	if(*s1 == 0)	return 0;
	return tolower(*(const unsigned char *)s1) - tolower(*(const unsigned char *)s2);
}
//深拷貝，根據str創建了一份拷貝
static char* cJSON_strdup(const char* str)
{
      size_t len;
      char* copy;

      len = strlen(str) + 1;
      if (!(copy = (char*)cJSON_malloc(len))) return 0;
      memcpy(copy,str,len);
      return copy;
}
//使用自定義內存分配函數，或者是系統內存分配函數，默認是malloc和free
void cJSON_InitHooks(cJSON_Hooks* hooks)
{
    if (!hooks) { /* Reset hooks */
        cJSON_malloc = malloc;
        cJSON_free = free;
        return;
    }

	cJSON_malloc = (hooks->malloc_fn)?hooks->malloc_fn:malloc;
	cJSON_free	 = (hooks->free_fn)?hooks->free_fn:free;
}
//返回比x大的最小的2的N次方數
static int pow2gt (int x)	{	--x;	x|=x>>1;	x|=x>>2;	x|=x>>4;	x|=x>>8;	x|=x>>16;	return x+1;	}

typedef struct {char *buffer; int length; int offset; } printbuffer;
//確保讀取的大小在字符串的範圍內; 如果需要的大小在總長度內,直接範圍偏移地址;如果不夠,則使用Pow2gt先申請更大的一塊
//,複製內容後,釋放原來的內存,再返回偏移值;
static char* ensure(printbuffer *p,int needed)
{
	char *newbuffer;int newsize;
	if (!p || !p->buffer) return 0;
	needed+=p->offset;
	if (needed<=p->length) return p->buffer+p->offset;

	newsize=pow2gt(needed);
	newbuffer=(char*)cJSON_malloc(newsize);
	if (!newbuffer) {cJSON_free(p->buffer);p->length=0,p->buffer=0;return 0;}
	if (newbuffer) memcpy(newbuffer,p->buffer,p->length);
	cJSON_free(p->buffer);
	p->length=newsize;
	p->buffer=newbuffer;
	return newbuffer+p->offset;
}
static int update(printbuffer *p)
{
	char *str;
	if (!p || !p->buffer) return 0;
	str=p->buffer+p->offset;
	return p->offset+strlen(str);
}
//將字符串轉換成16進制格式
static unsigned parse_hex4(const char *str)
{
	unsigned h=0;
	if (*str>='0' && *str<='9') h+=(*str)-'0'; else if (*str>='A' && *str<='F') h+=10+(*str)-'A'; else if (*str>='a' && *str<='f') h+=10+(*str)-'a'; else return 0;
	h=h<<4;str++;
	if (*str>='0' && *str<='9') h+=(*str)-'0'; else if (*str>='A' && *str<='F') h+=10+(*str)-'A'; else if (*str>='a' && *str<='f') h+=10+(*str)-'a'; else return 0;
	h=h<<4;str++;
	if (*str>='0' && *str<='9') h+=(*str)-'0'; else if (*str>='A' && *str<='F') h+=10+(*str)-'A'; else if (*str>='a' && *str<='f') h+=10+(*str)-'a'; else return 0;
	h=h<<4;str++;
	if (*str>='0' && *str<='9') h+=(*str)-'0'; else if (*str>='A' && *str<='F') h+=10+(*str)-'A'; else if (*str>='a' && *str<='f') h+=10+(*str)-'a'; else return 0;
	return h;
}
//跳過控制字符，asc碼小於33，包括\r\n
static const char *skip(const char *in) {while (in && *in && (unsigned char)*in<=32) in++; return in;}
//雙向鏈表節點互指
static void suffix_object(cJSON *prev,cJSON *item) {prev->next=item;item->prev=prev;}
cJSON *cJSON_Duplicate(cJSON *item,int recurse)
{
	cJSON *newitem,*cptr,*nptr=0,*newchild;
	/* Bail on bad ptr */
	if (!item) return 0;
	/* Create new item */
	newitem=cJSON_New_Item();
	if (!newitem) return 0;
	/* Copy over all vars */
	newitem->type=item->type&(~cJSON_IsReference),newitem->valueint=item->valueint,newitem->valuedouble=item->valuedouble;
	if (item->valuestring)	{newitem->valuestring=cJSON_strdup(item->valuestring);	if (!newitem->valuestring)	{cJSON_Delete(newitem);return 0;}}
	if (item->string)		{newitem->string=cJSON_strdup(item->string);			if (!newitem->string)		{cJSON_Delete(newitem);return 0;}}
	/* If non-recursive, then we're done! */
	if (!recurse) return newitem;
	/* Walk the ->next chain for the child. */
	cptr=item->child;
	while (cptr)
	{
		newchild=cJSON_Duplicate(cptr,1);		/* Duplicate (with recurse) each item in the ->next chain */
		if (!newchild) {cJSON_Delete(newitem);return 0;}
		if (nptr)	{nptr->next=newchild,newchild->prev=nptr;nptr=newchild;}	/* If newitem->child already set, then crosswire ->prev and ->next and move on */
		else		{newitem->child=newchild;nptr=newchild;}					/* Set newitem->child and move to it */
		cptr=cptr->next;
	}
	return newitem;
}

void cJSON_Minify(char *json)
{
	char *into=json;
	while (*json)
	{
		if (*json==' ') json++;
		else if (*json=='\t') json++;	/* Whitespace characters. */
		else if (*json=='\r') json++;
		else if (*json=='\n') json++;
		else if (*json=='/' && json[1]=='/')  while (*json && *json!='\n') json++;	/* double-slash comments, to end of line. */
		else if (*json=='/' && json[1]=='*') {while (*json && !(*json=='*' && json[1]=='/')) json++;json+=2;}	/* multiline comments. */
		else if (*json=='\"'){*into++=*json++;while (*json && *json!='\"'){if (*json=='\\') *into++=*json++;*into++=*json++;}*into++=*json++;} /* string literals, which are \" sensitive. */
		else *into++=*json++;			/* All other characters. */
	}
	*into=0;	/* and null-terminate. */
}

 

三、cJSON測試程序

#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("%s\n",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("%s\n",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("%s\n",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("%s\n",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("%s\n",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("%s\n",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\": 24\n}\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: */
    //解析傳入的字符串並以JSON格式數據輸出
	doit(text1);
	doit(text2);	
	doit(text3);
	doit(text4);
	doit(text5);
	/* Now some samplecode for building objects concisely: */
    //根據cJSON提供的接口手動構建層次樹並輸出
	create_objects();
	
	return 0;
}