c/c++ code JSON

cJSON 初体验

cJSON是一个超轻巧，携带方便，单文件，简单的可以作为ANSI-C标准的JSON解析器。
官网地址

cJSON.c

/*
  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.
*/

/* cJSON */
/* JSON parser in C. */

#include <string.h>
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <float.h>
#include <limits.h>
#include <ctype.h>
#include "cJSON.h"

static const char *ep;

const char *cJSON_GetErrorPtr(void) {return ep;}

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);
}

static void *(*cJSON_malloc)(size_t sz) = malloc;
static void (*cJSON_free)(void *ptr) = free;

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;
}

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;
}

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

/* Delete a cJSON structure. */
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;
    }
}

/* Parse the input text to generate a number, and populate the result into item. */
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 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;

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);
}

/* Render the number nicely from the given item into a string. */
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 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;
}

/* Parse the input text into an unescaped cstring, and populate item. */
static const unsigned char firstByteMark[7] = { 0x00, 0x00, 0xC0, 0xE0, 0xF0, 0xF8, 0xFC };
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! */

    while (*ptr!='\"' && *ptr && ++len) if (*ptr++ == '\\') ptr++;  /* Skip escaped quotes. */

    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++;
        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;
}

/* Render the cstring provided to an escaped version that can be printed. */
static char *print_string_ptr(const char *str,printbuffer *p)
{
    const char *ptr;char *ptr2,*out;int len=0,flag=0;unsigned char token;

    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++='\"';
        strcpy(ptr2,str);
        ptr2[len]='\"';
        ptr2[len+1]=0;
        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);}

/* Predeclare these prototypes. */
static const char *parse_value(cJSON *item,const char *value);
static char *print_value(cJSON *item,int depth,int fmt,printbuffer *p);
static const char *parse_array(cJSON *item,const char *value);
static char *print_array(cJSON *item,int depth,int fmt,printbuffer *p);
static const char *parse_object(cJSON *item,const char *value);
static char *print_object(cJSON *item,int depth,int fmt,printbuffer *p);

/* Utility to jump whitespace and cr/lf */
static const char *skip(const char *in) {while (in && *in && (unsigned char)*in<=32) in++; return in;}

/* Parse an object - create a new root, and populate. */
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));
    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;
}
/* Default options for cJSON_Parse */
cJSON *cJSON_Parse(const char *value) {return cJSON_ParseWithOpts(value,0,0);}

/* Render a cJSON item/entity/structure to text. */
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;
}


/* Parser core - when encountering text, process appropriately. */
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 parse_array(item,value); }
    if (*value=='{')                { return parse_object(item,value); }

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

/* Render a value to text. */
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)
        {
            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;
}

/* Build an array from input text. */
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. */
}

/* Render an array to text */
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; 
}

/* Build an object from the text. */
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. */

    item->child=child=cJSON_New_Item();
    if (!item->child) return 0;
    value=skip(parse_string(child,skip(value)));
    if (!value) return 0;
    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;

    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;
        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. */
}

/* Render an object to text. */
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;
    /* Count the number of entries. */
    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)
        {
            names[i]=str=print_string_ptr(child->string,0);
            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;
        }

        /* 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; 
}

/* 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;}

/* Duplication */
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. */
}

cJSON.h

/*
  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.
*/

#ifndef cJSON__h
#define cJSON__h

#ifdef __cplusplus
extern "C"
{
#endif

/* cJSON Types: */
#define cJSON_False 0
#define cJSON_True 1
#define cJSON_NULL 2
#define cJSON_Number 3
#define cJSON_String 4
#define cJSON_Array 5
#define cJSON_Object 6

#define cJSON_IsReference 256
#define cJSON_StringIsConst 512

/* 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;

typedef struct cJSON_Hooks {
      void *(*malloc_fn)(size_t sz);
      void (*free_fn)(void *ptr);
} cJSON_Hooks;

/* Supply malloc, realloc and free functions to cJSON */
extern void cJSON_InitHooks(cJSON_Hooks* 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);
/* Render a cJSON entity to text for transfer/storage. Free the char* when finished. */
extern char  *cJSON_Print(cJSON *item);
/* Render a cJSON entity to text for transfer/storage without any formatting. Free the char* when finished. */
extern char  *cJSON_PrintUnformatted(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 */
extern char *cJSON_PrintBuffered(cJSON *item,int prebuffer,int fmt);
/* Delete a cJSON entity and all subentities. */
extern void   cJSON_Delete(cJSON *c);

/* Returns the number of items in an array (or object). */
extern int    cJSON_GetArraySize(cJSON *array);
/* Retrieve item number "item" from array "array". Returns NULL if unsuccessful. */
extern cJSON *cJSON_GetArrayItem(cJSON *array,int item);
/* Get item "string" from object. Case insensitive. */
extern cJSON *cJSON_GetObjectItem(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. */
extern const char *cJSON_GetErrorPtr(void);

/* 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);

/* 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);

/* 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);  /* 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);

/* 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);

/* 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);

/* Macros for creating things quickly. */
#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))

/* When assigning an integer value, it needs to be propagated to valuedouble too. */
#define cJSON_SetIntValue(object,val)           ((object)?(object)->valueint=(object)->valuedouble=(val):(val))
#define cJSON_SetNumberValue(object,val)        ((object)?(object)->valueint=(object)->valuedouble=(val):(val))

#ifdef __cplusplus
}
#endif

#endif

Test代码

#include "stdio.h"
#include "cJSON.h"
//测试，解析一个json
void TestParse()
{
    char * jsonstr = "{\"a\":1,\"b\":\"ccc\",\"datalist\":[{\"id\":1,\"name\":\"xxxx\",\"age\":20},{\"id\":2,\"name\":\"xxxx1\",\"age\":21},{\"id\":3,\"name\":\"xxxx2\",\"age\":22}]}";
    printf("jsonstr is -> %s\n",jsonstr);
    cJSON * root;
    root = cJSON_Parse(jsonstr);
    if (root == 0){
        printf("Error before: [%s]\n",cJSON_GetErrorPtr());
        printf("%s\n",cJSON_Print(root));
    }
    int a = cJSON_GetObjectItem(root,"a")->valueint;
    printf("a=%d\n",a);
    char * b =  cJSON_GetObjectItem(root,"b")->valuestring;
    printf("b=%s\n",b);


    cJSON * datalist=0;
    datalist = cJSON_GetObjectItem(root,"datalist");
    if (datalist == 0){
        printf("err\n");
    }
    cJSON * tmp;
    int i = 0;
    tmp = cJSON_GetArrayItem(datalist,i);
    int id=0;int age=0;char* name=0;
    do{
        ++i;
        id = cJSON_GetObjectItem(tmp,"id")->valueint;
        name = cJSON_GetObjectItem(tmp,"name")->valuestring;
        age = cJSON_GetObjectItem(tmp,"age")->valueint;
        printf("id=%d,name=%s,age=%d\n",id,name,age);
    }while(tmp = cJSON_GetArrayItem(datalist,i));
}

//测试 创建一个json
void TestCreate()
{
    cJSON *root, *tmp;
    root = cJSON_CreateObject();            //创建root，并且初始化root下面的节点...
    cJSON_AddNumberToObject(root,"a",1);
    cJSON_AddStringToObject(root,"b","ccc");
    cJSON * arrtmp = cJSON_CreateArray();
    cJSON_AddItemToObject(root,"datalist",arrtmp);

    tmp = cJSON_CreateObject();
    cJSON_AddNumberToObject(tmp,"id",1);
    cJSON_AddStringToObject(tmp,"name","xxxx");
    cJSON_AddNumberToObject(tmp,"age",1);
    cJSON_AddItemToArray(arrtmp,tmp);

    tmp = cJSON_CreateObject();
    cJSON_AddNumberToObject(tmp,"id",2);
    cJSON_AddStringToObject(tmp,"name","xxxx1");
    cJSON_AddNumberToObject(tmp,"age",20);
    cJSON_AddItemToArray(arrtmp,tmp);


    tmp = cJSON_CreateObject();
    cJSON_AddNumberToObject(tmp,"id",3);
    cJSON_AddStringToObject(tmp,"name","xxxx2");
    cJSON_AddNumberToObject(tmp,"age",21);
    cJSON_AddItemToArray(arrtmp,tmp);

    printf("create json is:\n %s\n",cJSON_Print(root));

}

int main()
{
    TestParse();
    printf("\n==============================================================================================================================\n");
    TestCreate();
}

编译

执行结果