Linux C 编程——使用json-c库读取json格式的配置文件
1. 简介：
参考：
https://github.com/json-c/json-c/wiki
https://github.com/json-c/json-c
https://blog.csdn.net/u014530704/article/details/72674642?utm_source=copy
https://blog.csdn.net/w_ww_w/article/details/8295027
重点哈：https://blog.csdn.net/qimi123456/article/details/80426474
2. 编译运行：
json-c GitHub repo: https://github.com/json-c/json-c
$ git clone https://github.com/json-c/json-c.git $ cd json-c $ sh autogen.sh
followed by
$ ./configure # --enable-threading $ make $ make install
To build and run the test programs:
$ make check $ make USE_VALGRIND=0 check # optionally skip using valgrind
3. 简单测试
1. 测试前，创建配置文件test.json，内容如下：
[root@localhost tests]# cat test.json
{"cmd":"SetPwd","params":{"id":111,"password":"test"}}2. 编写测试文件test.c，内容如下：
#include
#include
#include
#include
#include "../json.h"
void main()
{
/*从文件中获取json对象*/
struct json_object * json_policy_array;
json_policy_array = json_object_from_file("./test.json");
printf("%s\n",json_object_to_json_string(json_policy_array));
/*从json对象中获取json对象*/
struct json_object * json_cmd ;
json_cmd = json_object_object_get(json_policy_array,"cmd");
printf("%s\n",json_object_to_json_string(json_cmd));
/*从json对象中获取json对象*/
struct json_object * json_params ;
json_params = json_object_object_get(json_policy_array,"params");
printf("%s\n",json_object_to_json_string(json_params));
int id = -1; //用于保存账号的值
int pwd_len = 0;
char *pwd = NULL; //用于保存密码的值
char *cmd = NULL; //用于保存cmd的值
/*从json对象中获取数据，首先获取对象，然后进行类型转换，转成int、float、string等*/
id = json_object_get_int(json_object_object_get(json_params,"id"));
printf("id = %d\n", id);
cmd = json_object_get_string(json_object_object_get(json_policy_array,"cmd"));
printf("cmd = %s\n", cmd);
pwd_len = json_object_get_string_len(json_object_object_get(json_params,"password"));
pwd = json_object_get_string(json_object_object_get(json_params,"password"));
printf("pwd_len = %d\n", pwd_len);
printf("pwd = %s\n", pwd);
/*向json文件中添加数据*/
//创建一个json对象newPobj
char *result = "OK";
//往json_policy_array里面添加键值对
json_object_object_add(json_policy_array,"result",json_object_new_string(result));
//创建一个json对象paramsProbj
json_object *paramsProbj = NULL;
paramsProbj = json_object_new_object();
//往paramsProbj里面添加键值对
json_object_object_add(paramsProbj,"id",json_object_new_int(200));
json_object_object_add(paramsProbj,"password",json_object_new_string("password2"));
//把paramsProbj添加到newPobj对象中
json_object_object_add(json_params,"paramsProbj",paramsProbj);
//这时还是将配置信息存在内存中呢
printf("%s\n",json_object_to_json_string(json_policy_array));
//将内存中修改后的配置文件，写会到磁盘中
json_object_to_file("./test.json",json_policy_array);
//释放内存
//引用计数方式，无需手动释放
} 3. 编译
[root@localhost tests]# gcc -ljson-c test.c
test.c: In function ‘main’:
test.c:32:6: warning: assignment discards ‘const’ qualifier from pointer target type [enabled by default]
cmd = json_object_get_string(json_object_object_get(json_policy_array,"cmd"));
^
test.c:36:6: warning: assignment discards ‘const’ qualifier from pointer target type [enabled by default]
pwd = json_object_get_string(json_object_object_get(json_params,"password"));
^4.运行
[root@localhost tests]# ./a.out
{ "cmd": "SetPwd", "params": { "id": 111, "password": "test" } }
"SetPwd"
{ "id": 111, "password": "test" }
id = 111
cmd = SetPwd
pwd_len = 4
pwd = test
{ "cmd": "SetPwd", "params": { "id": 111, "password": "test", "paramsProbj": { "id": 200, "password": "password2" } }, "result": "OK" }运行后，配置文件内容如下：
[root@localhost tests]# cat test.json
{"cmd":"SetPwd","params":{"id":111,"password":"test","paramsProbj":{"id":200,"password":"password2"}},"result":"OK"}4. 项目应用
在项目中，可以对此开源库进行封装，以使用项目本身；
为了是运行中的进程能够在配置文件改变后重新读取，需要引入信号机制：
1. 可以直接在信号处理函数中重新读取配置文件；
2. 也可以使用单独的线程，线程阻塞等待信号量，信号处理函数中释放信号量，线程获得信号量后，读写配置文件。