jansson 示例
安装jansson
./configure
make
make install
生成帮助文档
cd doc
make html
编译选项需要添加“-ljansson”
jansson 手册：
https://jansson.readthedocs.io/en/latest/index.html
API 介绍：
http://jansson.readthedocs.io/en/2.2/apiref.html#json_error_t
创建json对象与导出：
#include <stdio.h> #include <jansson.h> #include <stdint.h> #include <string.h> int main(int argc, char **argv) { //#构造 json数据 json_t *rootT = json_object(); json_t *item = json_object(); json_object_set_new(item, "name", json_string("xiaochen")); json_object_set_new(item, "age", json_integer(22)); /* json_object_set(rootT, "root", item); json_object_set会增加item对象的引用计数，一般用于添加到另一个json对象上。*/ json_object_set_new(rootT, "root", item); // json对象导出，转换成字符串。 char *pStrRoot = json_dumps(rootT, 0); json_delete(rootT); printf("pStrRoot:%s\n", pStrRoot); json_error_t error; json_t* root = json_object(); json_t* jsonArgsObj = json_loads(pStrRoot, 0, &error);//反序列化 json_object_set_new(root, "code", json_integer(0)); json_object_set_new(root, "message", json_string("strMessage")); json_object_set_new(root, "sdk", json_string("strApiName")); json_object_set_new(root, "args", jsonArgsObj); // json_object_set_new(root, "args", json_string(pStrRoot)); // json_object_set_new(root, "data", jsonDataObj); // json_decref(jsonArgsObj); char *json = json_dumps(root, JSON_INDENT(0)); //序列化 printf("json:%s\n", json); free(pStrRoot); // json_dumps返回的对象要手动释放。 free(json); // test get json object from one node of a json object json_t *js_args = json_object(); json_t *js_item = json_object_get(root, "args"); if(!json_is_object(js_item)) { printf("js not a object.\n"); return 0; } /*js_item对象来自root，将其添加到另外一个对象时需要使用json_object_set增加其引用计数。 此处不可使用json_object_set_new。*/ //json_object_set_new(js_args, "newArgs", js_item); json_object_set(js_args, "newArgs", js_item); json = json_dumps(js_args, JSON_INDENT(0)); //序列化 printf("json:%s\n", json); free(json); // json_object_del(js_args, "newArgs"); // json_object_clear(js_args); json_decref(js_args); // json_delete(root); json_decref(root); // printf("jsonArgsObj result:%p\n", jsonArgsObj); // if(jsonArgsObj) // { //// json_decref(jsonArgsObj); //// jsonArgsObj = NULL; // } // printf("again jsonArgsObj result:%p\n", jsonArgsObj); return 0; }
string object array error number
#include <stdio.h> #include <stdlib.h> #include <stdfix.h> #include <string.h> #include <iostream> #include <jansson.h> #include <jansson_config.h> using namespace std; int main() { json_t val; json_type eval = JSON_REAL; bool Judge = 1; int type = json_typeof(&val); // Get the type of Obj Judge = json_is_object(&val); // Obj Judge cout << "json_is_object:" << Judge << endl; Judge = json_is_array(&val); //Object judged to be array cout << "Json_is_array:" << Judge << endl; cout << "The type of val:" << type << endl; /* JSON array Defination and value setting */ json_t *array, *integer; array = json_array(); // Create the json array integer = json_integer(42); // Create the json integer json_array_append(array,integer); // Set the value of json array json_decref(integer); // Drop the content of integer and can no longer be used. /* JSON-STRING */ json_auto_t *value = NULL; value = json_string("Hello"); // Initial a new string json obj json_string_set(value, "World!"); // Use set func to change the content of json string obj. size_t len = json_string_length(value); // Get the length of the json string obj. cout << "The len of value:" << len << endl; /* JSON-NUMBER */ json_int_t number; // Define a json type number. number = 100; // initial the number. printf("number is %" JSON_INTEGER_FORMAT "\n",number); number = json_integer_value(integer); // Get the json type integer's value to number. printf("value of integer(json_t) is %" JSON_INTEGER_FORMAT "\n",number); // The integer had been decrefed in line27.(So it's zero) integer = json_real(3.1415926); // Set a real number value to integer. double res = json_real_value(integer); // Read out the value to a double type var.(The integer can store the double type json data.) printf("The res is:%f\n",res); /* JSON-ARRAY */ json_t *Matrix = json_array(); // json array defination. json_array_append(Matrix,integer); // Add a integer obj to the array. size_t Matrix_Size = json_array_size(Matrix); // Test the size of the array after add a new integer obj to it. printf("The size of Matrix:%d\n",Matrix_Size); /* JSON-OBJECT */ json_t *obj = json_object(); // Define a new json obj. size_t obj_size = json_object_size(obj); // Get the size of the json obj. printf("The size of obj:%d\n",obj_size); char *key = "Hello"; integer = json_integer(52); // Set the value of integer json obj. int back = json_object_set(obj,key,integer); // Setup a new obj named "Hello" and the mapped value is 52. json_t *read_num_back = json_object_get(obj,key); // Get back the obj named "Hello". int num_val = json_integer_value(read_num_back); // Get the value of the Hello obj. cout << "The value of integer:" << num_val << endl; // Echo out the Value. while(1); return 0; }
#include<stdio.h> #include<string.h> #include<jansson.h> #define FILE_PATH "./temp.txt" #define MAX_NUM 5 typedef struct _JSON_ITEM_INFO { json_t* string; json_t* value; }JSON_ITEM_INFO; void save_info_to_file() { json_t* root = NULL; json_t* item_1 = NULL; json_t* item_2 = NULL; json_t* item_3 = NULL; json_t* array = NULL; char* s_repon = NULL; root = json_object(); item_1 = json_object(); item_2 = json_object(); item_3 = json_object(); array = json_array(); json_object_set_new(item_1,"name",json_string("xiaopeng")); json_object_set_new(item_1,"age",json_integer(12)); json_array_append_new(array,item_1); json_object_set_new(item_2,"name",json_string("xiaoming")); json_object_set_new(item_2,"age",json_integer(8)); json_array_append_new(array,item_2); json_object_set_new(item_3,"name",json_string("xiaohong")); json_object_set_new(item_3,"age",json_integer(22)); json_array_append_new(array,item_3); json_object_set_new(root,"root",array); json_dump_file(root, FILE_PATH,JSON_PRESERVE_ORDER); s_repon = json_dumps(root,JSON_INDENT(0)); printf("s_repon = %s \n",s_repon); free(s_repon); printf("size = %d \n", (int)json_array_size(array)); if(root) { json_delete(root); } if(array) { json_delete(array); } } void get_file_info() { int i = 0; json_t* root = NULL; json_t* array = NULL; json_error_t error; char* s_repon = NULL; json_t* add_item_1 = NULL; char* s_get_add_item = NULL; json_t* rec_table[MAX_NUM] = {0}; JSON_ITEM_INFO person[MAX_NUM]; memset(person,0,sizeof(person)); //get the info from file; root = json_load_file(FILE_PATH, 0, &error); if(!json_is_object(root)) { printf("%s,%d\n",__FILE__,__LINE__); } s_repon = json_dumps(root,JSON_INDENT(0)); printf("s_repon = %s \n",s_repon); free(s_repon); array = json_object_get(root,"root"); if(!json_is_array(array)) { printf("%s,%d\n",__FILE__,__LINE__); } for(i = 0; i < MAX_NUM ;i++) { rec_table[i] = json_array_get(array,i); if(!json_is_object(rec_table[i])) { printf("%s,%d\n",__FILE__,__LINE__); } person[i].string = json_object_get(rec_table[i],"name"); printf("person[%d].string = %s \n",i,json_string_value(person[i].string)); person[i].value = json_object_get(rec_table[i],"age"); printf("person[%d].value = %d \n",i,(int)json_integer_value(person[i].value)); } //add the new item; add_item_1 = json_object(); json_object_set_new(add_item_1,"name",json_string("zhangsan")); json_object_set_new(add_item_1,"age",json_integer(30)); if(json_array_size(array) >= MAX_NUM) { //remove the top item; json_array_remove(array,0); } json_array_append_new(array,add_item_1); //write the new array to the file; json_dump_file(root, FILE_PATH,JSON_PRESERVE_ORDER); //dump the date and print s_get_add_item = json_dumps(root,JSON_INDENT(0)); printf("s_get_add_item = %s \n",s_get_add_item); free(s_get_add_item); } int main() { save_info_to_file(); //这里将数据保存在文件 FILE_PATH 里； get_file_info(); // 这里将文件 FILE_PATH 数据读取出来； return 0; }
编译：
gcc source.c -ljansson
