一、Jansson的安装：
这里可以直接参考Jansson官方手册第一步：https://jansson.readthedocs.io/en/2.13/gettingstarted.html
这里暂时介绍在Window条件下，使用CMake+Mingw32配置Jansson库。
1.直接使用指令的方式，在CMD中按照以下指令操作(使用这种方式跳过步骤2)：
<Uncompress the tar.gz File> cd jansson-2.13.1 md build cd build cmake -G "MinGW Makefiles" .. mingw32-make
mingw32-make install
上述等待完成CMake之后生成对应的Makefile，然后再调用make命令，完成对应程序的编译。
2.使用CMake GUI来进行编译(一般大家在Windows上都是安装的CMake的GUI)
注1：注意取消勾选JANSSON_BUILD_DOCS.
注2：注意勾选JANSSON_BUILD_SHRAED_LIBS.这里的勾选非常重要，否则将不会生成对应Windows的dll动态库文件，无法调用Jansson相关的API。
最后调用mingw32-make完成Jansson库的编译过程.
完成编译之后使用make install完成对编译的库进行安装，如下：
mingw32-make.exe install
3.配置Jansson库的环境变量
打开PATH路径在其中添加如下环境变量：
这个是环境变量的前缀设置，避免PATH过长的情况。
这里是在PATH添加的环境变量，这里添加的是mingw32-make install之后的安装位置的库路径。
在VSC中配置相关Jansson库，如下所示：
1 c_cpp_properties.json添加: 2 "C:/Program Files (x86)/jansson/include", 3 tasks.json添加: 4 "-IC:/Program Files (x86)/jansson/include", 5 "-LC:/Program Files (x86)/jansson/bin/*", 6 "-LC:/Program Files (x86)/jansson/lib", 7 "-llibjansson",
具体参照这里，里面包括了Opencv，不使用Opencv的话，删除Opencv相关内容即可：
c_cpp_properties.json文件内容：
{ "configurations": [ { "name": "Win32", "includePath": [ "${workspaceFolder}/**", "D:/TDM-GCC-64/include/*", "D:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/include/c++/*", "D:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/include/c++/x86_64-w64-mingw32/*", "D:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/include/c++/backward/*", "D:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/include/*", "D:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/include-fixed", "D:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/../../../../x86_64-w64-mingw32/include", "C:/Program Files (x86)/jansson/include", "D:/Opencv/opencv/mingw64_build/install/include", "D:/Opencv/opencv/mingw64_build/install/include/opencv2" ], "defines": [], "compilerPath":"D:/TDM-GCC-64/bin/gcc.exe", "cStandard": "c11", "cppStandard": "c++17", "intelliSenseMode": "clang-x64", "browse": { "path": [ "${workspaceFolder}", "D:/TDM-GCC-64/include/**", "D:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/include", "D:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/9.2.0/include/c++", "D:/Opencv/opencv/mingw64_build/install/include", "C:/Program Files (x86)/jansson/include" ], "limitSymbolsToIncludedHeaders": true, "databaseFilename": "" } } ], "version": 4 }
tasks.json文件内容：
{ "version": "2.0.0", "command": "g++", "args": [ "-g", "${file}", "-o", "${fileBasenameNoExtension}.exe", "-ID:/Opencv/opencv/mingw64_build/install/include", "-ID:/Opencv/opencv/mingw64_build/install/include/opencv2", "-LD:/Opencv/opencv/mingw64_build/install/x64/mingw/lib", "-LD:/Opencv/opencv/mingw64_build/install/x64/mingw/bin/*", "-IC:/Program Files (x86)/jansson/include", "-LC:/Program Files (x86)/jansson/bin/*", "-LC:/Program Files (x86)/jansson/lib", "-llibjansson", "-llibopencv_calib3d420", "-llibopencv_core420", "-llibopencv_dnn420", "-llibopencv_features2d420", "-llibopencv_flann420", "-llibopencv_highgui420", "-llibopencv_imgcodecs420", "-llibopencv_imgproc420", "-llibopencv_ml420", "-llibopencv_objdetect420", "-llibopencv_photo420", "-llibopencv_stitching420", "-llibopencv_video420", "-llibopencv_videoio420", ], "problemMatcher": { "owner": "cpp", "fileLocation": [ "relative", "${workspaceFolder}" ], "pattern": { "regexp": "^(.*):(\\d+):(\\d+):\\s+(warning|error):\\s+(.*)$", "file": 1, "line": 2, "column": 3, "severity": 4, "message": 5 } }, "group": { "kind": "build", "isDefault": true } }
4.测试Jansson安装情况(注意第六行，导入jansson为绝对路径导入)
1 #include <stdio.h> 2 #include <stdlib.h> 3 #include <stdfix.h> 4 #include <string.h> 5 #include <iostream> 6 #include <jansson.h> 7 8 using namespace std; 9 10 int main(void) 11 { 12 json_t val; 13 int type = json_typeof(&val); 14 bool Judge = json_is_object(&val); 15 std::cout << "json_is_object:" << Judge << std::endl; 16 printf("Hello Jansson!\n"); 17 while(1); 18 return 0; 19 }
运行结果如下：
二、jansson相关的API：
https://jansson.readthedocs.io/en/latest/apiref.html#c.json_t
string object array error number
1 #include <stdio.h> 2 #include <stdlib.h> 3 #include <stdfix.h> 4 #include <string.h> 5 #include <iostream> 6 #include <jansson.h> 7 #include <jansson_config.h> 8 9 using namespace std; 10 11 int main() { 12 json_t val; 13 json_type eval = JSON_REAL; 14 bool Judge = 1; 15 int type = json_typeof(&val); // Get the type of Obj 16 Judge = json_is_object(&val); // Obj Judge 17 cout << "json_is_object:" << Judge << endl; 18 Judge = json_is_array(&val); //Object judged to be array 19 cout << "Json_is_array:" << Judge << endl; 20 cout << "The type of val:" << type << endl; 21 22 /* JSON array Defination and value setting */ 23 json_t *array, *integer; 24 array = json_array(); // Create the json array 25 integer = json_integer(42); // Create the json integer 26 json_array_append(array,integer); // Set the value of json array 27 json_decref(integer); // Drop the content of integer and can no longer be used. 28 29 /* JSON-STRING */ 30 json_auto_t *value = NULL; 31 value = json_string("Hello"); // Initial a new string json obj 32 json_string_set(value, "World!"); // Use set func to change the content of json string obj. 33 size_t len = json_string_length(value); // Get the length of the json string obj. 34 cout << "The len of value:" << len << endl; 35 36 /* JSON-NUMBER */ 37 json_int_t number; // Define a json type number. 38 number = 100; // initial the number. 39 printf("number is %" JSON_INTEGER_FORMAT "\n",number); 40 number = json_integer_value(integer); // Get the json type integer's value to number. 41 printf("value of integer(json_t) is %" JSON_INTEGER_FORMAT "\n",number); // The integer had been decrefed in line27.(So it's zero) 42 integer = json_real(3.1415926); // Set a real number value to integer. 43 double res = json_real_value(integer); // Read out the value to a double type var.(The integer can store the double type json data.) 44 printf("The res is:%f\n",res); 45 46 /* JSON-ARRAY */ 47 json_t *Matrix = json_array(); // json array defination. 48 json_array_append(Matrix,integer); // Add a integer obj to the array. 49 size_t Matrix_Size = json_array_size(Matrix); // Test the size of the array after add a new integer obj to it. 50 printf("The size of Matrix:%d\n",Matrix_Size); 51 52 /* JSON-OBJECT */ 53 json_t *obj = json_object(); // Define a new json obj. 54 size_t obj_size = json_object_size(obj); // Get the size of the json obj. 55 printf("The size of obj:%d\n",obj_size); 56 char *key = "Hello"; 57 integer = json_integer(52); // Set the value of integer json obj. 58 int back = json_object_set(obj,key,integer); // Setup a new obj named "Hello" and the mapped value is 52. 59 json_t *read_num_back = json_object_get(obj,key); // Get back the obj named "Hello". 60 int num_val = json_integer_value(read_num_back); // Get the value of the Hello obj. 61 cout << "The value of integer:" << num_val << endl; // Echo out the Value. 62 63 while(1); 64 return 0; 65 }
程序运行结果：
三、jansson处理JSON文件：
首先取JSON文件test.json如下：
1 { 2 "deviceList": [{ 3 "id": "fee5e04c50754088913601d733aadea5", 4 "name": "Company", 5 "anotherName": "", 6 "groupName": "Reseach", 7 "serial": "03307186819I", 8 "batch": 0, 9 "model": "A-610", 10 "ipAddr": "123.54.90.133", 11 "macAddr": "", 12 "status": 0, 13 "isLock": false, 14 "comment": "", 15 "createTime": "Jul 15, 2019 1:43:51 PM", 16 "icreateTime": "", 17 "heartPort": 12671, 18 "voltagePort": 12672, 19 "statusPort": 12673, 20 "historyPort": 12674, 21 "statisticPort": 12675, 22 "logPort": 12676, 23 "paramPort": 12677, 24 "lockPort": 12678, 25 "updatePort": 12679, 26 "sn": 224, 27 "projectName": "Lib" 28 }, { 29 "id": "cb14cfe4c2874c7387119048dc4f9fe0", 30 "name": "Company", 31 "anotherName": "", 32 "groupName": "xxx", 33 "serial": "0450019sd89K", 34 "batch": 0, 35 "model": "SM-100", 36 "ipAddr": "229.168.20.221", 37 "macAddr": "", 38 "status": 0, 39 "isLock": false, 40 "comment": "", 41 "createTime": "Nov 14, 2019 4:07:55 PM", 42 "icreateTime": "", 43 "heartPort": 18341, 44 "voltagePort": 18342, 45 "statusPort": 18343, 46 "historyPort": 18344, 47 "statisticPort": 18345, 48 "logPort": 18346, 49 "paramPort": 18347, 50 "lockPort": 18348, 51 "updatePort": 18349, 52 "sn": 790, 53 "projectName": "" 54 }, { 55 "id": "c149edf863074005876da6a5a22bc9b8", 56 "name": "Company", 57 "anotherName": "", 58 "groupName": "xxx", 59 "serial": "04510190118K", 60 "batch": 0, 61 "model": "SM-100", 62 "ipAddr": "201.168.23.48", 63 "macAddr": "", 64 "status": 0, 65 "isLock": false, 66 "comment": "", 67 "createTime": "Nov 29, 2019 4:13:49 PM", 68 "icreateTime": "", 69 "heartPort": 19631, 70 "voltagePort": 19632, 71 "statusPort": 19633, 72 "historyPort": 19634, 73 "statisticPort": 19635, 74 "logPort": 19636, 75 "paramPort": 19637, 76 "lockPort": 19638, 77 "updatePort": 19639, 78 "sn": 979, 79 "projectName": "" 80 }], 81 "url":"www.baidu.com", 82 "frequency":50 83 }
其中包括了数组array格式数据，整数、字符串等。
以下代码对此Json文件进行了各方面的解析，具体如下：
1 #include <stdio.h> 2 #include <stdlib.h> 3 #include <stdfix.h> 4 #include <string.h> 5 #include <iostream> 6 #include <jansson.h> 7 #include <jansson_config.h> 8 9 using namespace std; 10 11 int main(void) 12 { 13 printf("Hello Jansson!\n"); 14 json_t val; 15 int type = json_typeof(&val); 16 bool Judge = json_is_object(&val); 17 std::cout << "json_is_object:" << Judge << std::endl; 18 19 json_error_t error; // Jansson Error Datatype. 20 json_t *json_file; // Josn File Point. 21 22 /* Read a JSON mesg from file.json */ 23 json_file = json_load_file("C:/Users/Administrator/Desktop/mamiao/Alg_Cpp/test.json", 0, &error); // Load json form json.json 24 if(!json_file) printf("No json_file can read!\n"); // Judge the file is right readed. 25 26 size_t obj_size = json_object_size(json_file); // Judge the number of the objects(deviceList\url\HEHE). 27 printf("The size of json_file:%d\n",obj_size); 28 29 const char *Key_0 = "url"; // Set the key value 30 json_t *url = json_object_get(json_file,Key_0); // Get the key mapped Json_object data. 31 32 Judge = json_is_string(url); // Judge the obj is string or not? 33 std::cout << "json_is_string:" << Judge << std::endl; 34 35 size_t str_length = json_string_length(url); // Get the length of the string obj. 36 std::cout << "The length of url is:" << str_length << std::endl; 37 38 const char *str_res_0 = " "; // Alloc the memory buffer for storage the data of json_object url. 39 str_res_0 = json_string_value(url); // Get the value of json_object url. 40 cout << "The length of url is:" << strlen(str_res_0) << endl; 41 for(int i=0;i<strlen(str_res_0);i++){ // Echo out the url string 42 cout << *(str_res_0+i); 43 } 44 cout << endl; 45 46 /* Get JSON's array value */ 47 const char *Key_1 = "deviceList"; 48 json_t *device = json_object_get(json_file,Key_1); // Get the deviceList array first 49 Judge = json_is_array(device); // Judge the data to be array 50 std::cout << "json_is_array:" << Judge << std::endl; 51 52 size_t array_size = json_array_size(device); // Get the size of array 53 cout << "The size of device array is:" << array_size << endl; // Echo out the size of deviceList array 54 55 json_t *device_0 = json_array_get(device,1); // Get the Element of deviceList array where the index=1 56 57 const char *Param1 = "id"; // Set the data type you need to get in deviceList_array[1] 58 json_t *id = json_object_get(device_0,Param1); // Get the id(type) data 59 Judge = json_is_string(id); // Judge the data is the right type(string\number\boolean...) 60 std::cout << "json_is_string:" << Judge << std::endl; 61 62 const char *id_string = " "; // Alloc the memory buffer for storage the data of json_object id. 63 id_string = json_string_value(id); // Convert the value to Cpp's string type. 64 cout << "The length of id is:" << strlen(id_string) << endl; // Checkout the length of the string. 65 for(int i=0;i<strlen(id_string);i++){ // Show the string on the Terminal. 66 cout << *(id_string+i); 67 } 68 cout << endl; 69 70 /* Get the number value in this JSON */ 71 const char *Key_2 = "frequency"; // // Set the data type you need to get in json_file obj. 72 json_t *Freq = json_object_get(json_file,Key_2); // Get the frequency obj. 73 Judge = json_is_integer(Freq); // Judge the data is integer or not? 74 cout << "The frequency obj is integer:" << Judge << endl; 75 int Freq_val = json_number_value(Freq); // Get the value of frequency obj. 76 cout << "The value of Freq:" << Freq_val << endl; // Echo out the value. 77 78 /* Boolean object in JSON read */ 79 const char *Param2 = "isLock"; // Set the data type you need to get in deviceList_array[1] 80 json_t *Lock_state = json_object_get(device_0,Param2); // Get the isLock(type) status 81 Judge = json_is_boolean(Lock_state); // Judge the data is the right type(string\number\boolean...) 82 std::cout << "json_is_boolean:" << Judge << std::endl; 83 bool state = json_boolean_value(Lock_state); // Get the status of the isLock bool data. 84 if(state){ // Echo out the result. 85 cout << "It's True." << endl; 86 }else{ 87 cout << "It's False." << endl; 88 } 89 90 while(1); 91 return 0; 92 }
在我的设备上运行的结果如下：
四、从网上获取JSON文件并解析：
未完待续~
Reference：
github官网代码下载：https://github.com/akheron/jansson
Jansson官方主页面：https://digip.org/jansson/
Jansson编程手册：https://jansson.readthedocs.io/en/2.13/tutorial.html
转载请注明出处！感谢GISPALAB实验室的老师和同学们的帮助和支持~
