c++ 使用json的库。cJSON

cJSON官网是：http://sourceforge.net/projects/cjson/?source=recommended

最新版本是2013年的，与2009年的变化不是很大。

看了代码，觉得挺好，只是是C语言的，不够好。

就改良了一下，内存自己管理。使用std::string 

http://files.cnblogs.com/ayanmw/cJSON_cpp_myversion.zip

使用起来如下：

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

#define PS(V) printf(#V"=%s
",V);
#define PI(V) printf(#V"=%d
",V);
#define PF(V) printf(#V"=%f
",V);

int main (int argc, const char * argv[]) {
    AddStack(__FUNCTION__);
    
    const char * myjson="{"name":"value","jsonobject":{"int":5,"true":true,"false":false,"null":null},"jsonarray":["array1","array2",12,true,false,null,"12",-1.2]}";
    cJSON * jsonroot =new cJSON();
    if(0==jsonroot->cJSON_Parse(myjson))
        printf("Error to cJSON_Parse :%s %x
",jsonroot->cJSON_GetErrorPtr(),jsonroot->cJSON_GetErrorPtr());
    else{
        const char * out=jsonroot->cJSON_Print( ).c_str();
        printf("myjson=%s
",out); 
        PS(jsonroot->toString().c_str());
        const char * value=jsonroot->cJSON_GetString( "name").c_str();
        PS(value);
        
        cJSON *jsonobject=jsonroot->cJSON_GetObjectItem( "jsonobject");
        PS(jsonroot->cJSON_GetString("jsonobject").c_str());
        PS(jsonobject->toString().c_str());
        
        PS(jsonobject->cJSON_GetString("null").c_str());
        PS(jsonobject->cJSON_GetString("int").c_str());
        PS(jsonobject->cJSON_GetString("true").c_str());
        
         
        PI(jsonobject->cJSON_GetInt("int") ); 
        PI(jsonobject->cJSON_GetBoolean("true")); 
        PI( jsonobject->cJSON_GetBoolean("false") ); 
        
        cJSON *jsonarray=jsonroot->cJSON_GetObjectItem("jsonarray");
        PS(jsonroot->cJSON_GetString("jsonarray").c_str());
        PS(jsonarray->toString().c_str());
        
        PI( jsonroot->cJSON_GetArraySize( ) );
        PI( jsonobject->cJSON_GetArraySize( ) );
        PI(jsonarray->cJSON_GetArraySize( ));
        
        cJSON *arrayitem=jsonarray->cJSON_GetArrayItem( 0); 
        PS(arrayitem->valuestring);
    }
    PS("END Mark");
    delete jsonroot;
    return 0;
}

toString()可以轻松获取到json的内容信息。以上是解析的。

生成json可以看cJSON的test.c 文件。

#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]
",cJSON_GetErrorPtr());}
    else
    {
        out=cJSON_Print(json);
        cJSON_Delete(json);
        printf("%s
",out);
        free(out);
    }
}

/* Read a file, parse, render back, etc. */
void dofile(char *filename)
{
    FILE *f=fopen(filename,"rb");fseek(f,0,SEEK_END);long len=ftell(f);fseek(f,0,SEEK_SET);
    char *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. */

    /* 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
",out);    free(out);    /* Print to text, Delete the cJSON, print it, release the string. */

    /* Our "days of the week" array: */
    const char *strings[7]={"Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"};
    root=cJSON_CreateStringArray(strings,7);

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

    /* Our matrix: */
    int numbers[3][3]={{0,-1,0},{1,0,0},{0,0,1}};
    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
",out);    free(out);


    /* Our "gallery" item: */
    int ids[4]={116,943,234,38793};
    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
",out);    free(out);

    /* 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"}};

    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
",out);    free(out);

}

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

    /* 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;
}

感觉比jsoncpp 代码简洁。算法看起来都是简单精炼的。很好的。