此範例會先產生如下的 json，並讀取此 json 做顯示。
{
"NULL":null,
"BOOLEAN":true,
"STRING":"string",
"NUMBER":100,
"DOUBLE":3.141593,
"ARRAY":[ "str1", "str2", "str3" ],
"OBJECT":{
"MEMBER_NULL":null,
"MEMBER_BOOLEAN":false,
"MEMBER_STRING":"string",
"MEMBER_NUMBER":200,
"MEMBER_DOUBLE":0.123457,
"MEMBER_ARRAY":[ 1, 2, 3 ]
}
}
測試步驟 (此測試以 ubuntu 16.04.1 為測試環境)
1. 安裝 json-c library
apt install apt-get install libjson-c-dev
2. 確認安裝 json-c library
apt show libjson-c-dev
3. 將底下範例存成 example_json.c
4. 編譯程式
gcc -o example_json example_json.c -ljson-c
5. 執行程式
./example_json
6. 檢查產生的 json
cat example.json
7. 可以將 example.json 的內容貼到 json formatter 來重整格式，方便閱讀
範例說明：
1. 函式 json_object_put() 用來釋放 json_object 配置的記憶體，呼叫原則是
a. 函式 json_object_from_file() 讀取 json 檔時產生的 json_object
b. 使用函式
json_object_new_object(),
json_object_new_boolean(),
json_object_new_string()
json_object_new_int(),
json_object_new_double(),
json_object_new_array()
產生的 json_object，但是如果有呼叫
json_object_object_add(),
json_object_array_add()
等函式則不用再呼叫 json_object_put()，
因為 json_object 已經被加入到另一個 json_object (例如底下範例的 json_obj) 中
範例：
json_object_new_array()
產生的 json_object，但是如果有呼叫
json_object_object_add(),
json_object_array_add()
等函式則不用再呼叫 json_object_put()，
因為 json_object 已經被加入到另一個 json_object (例如底下範例的 json_obj) 中
範例：
#include<stdio.h>
#include<json-c/json.h>
#define EXAMPLE_JSON "./example.json"
#define NULL_NULL "NULL"
#define BOOL_BOOLEAN "BOOLEAN"
#define STR_STRING "STRING"
#define NUM_INTEGER "NUMBER"
#define NUM_DOUBLE "DOUBLE"
#define ARR_ARRAY "ARRAY"
#define OBJ_OBJECT "OBJECT"
#define NULL_MEMBER_NULL "MEMBER_NULL"
#define BOOL_MEMBER_BOOLEAN "MEMBER_BOOLEAN"
#define STR_MEMBER_STRING "MEMBER_STRING"
#define NUM_MEMBER_INTEGER "MEMBER_NUMBER"
#define NUM_MEMBER_DOUBLE "MEMBER_DOUBLE"
#define ARR_MEMBER_ARRAY "MEMBER_ARRAY"
int write_to_json_file(char* filename)
{
int ret = 0;
json_object *json_obj = NULL;
json_object *array_obj = NULL;
json_object *new_obj = NULL;
json_object *tmp_obj = NULL;
json_object *tmp1_obj = NULL;
//new a base object
json_obj = json_object_new_object();
if (!json_obj)
{
printf("Cannot create object\n");
ret = -1;
goto error;
}
//new a null
json_object_object_add(json_obj, NULL_NULL, NULL);
//new a boolean
tmp_obj = json_object_new_boolean(1);
if (!tmp_obj)
{
printf("Cannot create boolean object for %s\n", BOOL_BOOLEAN);
ret = -1;
goto error;
}
json_object_object_add(json_obj, BOOL_BOOLEAN, tmp_obj);
tmp_obj = NULL;
//new a string
tmp_obj = json_object_new_string("string");
if (!tmp_obj)
{
printf("Cannot create string object for %s\n", STR_STRING);
ret = -1;
goto error;
}
json_object_object_add(json_obj, STR_STRING, tmp_obj);
tmp_obj = NULL;
//new a integer
tmp_obj = json_object_new_int(100);
if (!tmp_obj)
{
printf("Cannot create number object for %s\n", NUM_INTEGER);
ret = -1;
goto error;
}
json_object_object_add(json_obj, NUM_INTEGER, tmp_obj);
tmp_obj = NULL;
//new a double
tmp_obj = json_object_new_double(3.1415926);
if (!tmp_obj)
{
printf("Cannot create double object for %s\n", NUM_DOUBLE);
ret = -1;
goto error;
}
json_object_object_add(json_obj, NUM_DOUBLE, tmp_obj);
tmp_obj = NULL;
//new a array
array_obj = json_object_new_array();
if (!array_obj)
{
printf("Cannot create array object\n");
ret = -1;
goto error;
}
//new a string and add to the array
new_obj = json_object_new_string("str1");
if (!new_obj)
{
printf("Cannot create string object for %s\n", ARR_ARRAY);
ret = -1;
goto error;
}
json_object_array_add(array_obj, new_obj);
new_obj = NULL;
//new a string and add to the array
new_obj = json_object_new_string("str2");
if (!new_obj)
{
printf("Cannot create string object for %s\n", ARR_ARRAY);
ret = -1;
goto error;
}
json_object_array_add(array_obj, new_obj);
new_obj = NULL;
//new a string and add to the array
new_obj = json_object_new_string("str3");
if (!new_obj)
{
printf("Cannot create string object for %s\n", ARR_ARRAY);
ret = -1;
goto error;
}
json_object_array_add(array_obj, new_obj);
new_obj = NULL;
//add array to the base object
json_object_object_add(json_obj, ARR_ARRAY, array_obj);
array_obj = NULL;
//new an object
tmp_obj = json_object_new_object();
if (!tmp_obj)
{
printf("Cannot create object\n");
ret = -1;
goto error;
}
//add a null to the object
json_object_object_add(tmp_obj, NULL_MEMBER_NULL, NULL);
//new a boolean and add to the object
tmp1_obj = json_object_new_boolean(0);
if (!tmp1_obj)
{
printf("Cannot create boolean object for %s\n", BOOL_MEMBER_BOOLEAN);
ret = -1;
goto error;
}
json_object_object_add(tmp_obj, BOOL_MEMBER_BOOLEAN, tmp1_obj);
tmp1_obj = NULL;
//new a string and add to the object
tmp1_obj = json_object_new_string("string");
if (!tmp1_obj)
{
printf("Cannot create string object for %s\n", STR_MEMBER_STRING);
ret = -1;
goto error;
}
json_object_object_add(tmp_obj, STR_MEMBER_STRING, tmp1_obj);
tmp1_obj = NULL;
//new a integer and add to the object
tmp1_obj = json_object_new_int(200);
if (!tmp1_obj)
{
printf("Cannot create number object for %s\n", NUM_MEMBER_INTEGER);
ret = -1;
goto error;
}
json_object_object_add(tmp_obj, NUM_MEMBER_INTEGER, tmp1_obj);
tmp1_obj = NULL;
//new a double and add to the object
tmp1_obj = json_object_new_double(0.123456789);
if (!tmp1_obj)
{
printf("Cannot create double object for %s\n", NUM_MEMBER_DOUBLE);
ret = -1;
goto error;
}
json_object_object_add(tmp_obj, NUM_MEMBER_DOUBLE, tmp1_obj);
tmp1_obj = NULL;
//new a array
array_obj = json_object_new_array();
if (!array_obj)
{
printf("Cannot create array object\n");
ret = -1;
goto error;
}
//new a integer and add to array
new_obj = json_object_new_int(1);
if (!new_obj)
{
printf("Cannot create string object for %s\n", ARR_MEMBER_ARRAY);
ret = -1;
goto error;
}
json_object_array_add(array_obj, new_obj);
new_obj = NULL;
//new a integer and add to array
new_obj = json_object_new_int(2);
if (!new_obj)
{
printf("Cannot create string object for %s\n", ARR_MEMBER_ARRAY);
ret = -1;
goto error;
}
json_object_array_add(array_obj, new_obj);
new_obj = NULL;
//new a integer and add to array
new_obj = json_object_new_int(3);
if (!new_obj)
{
printf("Cannot create string object for %s\n", ARR_MEMBER_ARRAY);
ret = -1;
goto error;
}
json_object_array_add(array_obj, new_obj);
new_obj = NULL;
//add array to the object
json_object_object_add(tmp_obj, ARR_MEMBER_ARRAY, array_obj);
array_obj = NULL;
//add the object to base object
json_object_object_add(json_obj, OBJ_OBJECT, tmp_obj);
tmp_obj = NULL;
//write the base object to write.json
json_object_to_file(filename, json_obj);
error:
json_object_put(tmp1_obj);
json_object_put(tmp_obj);
json_object_put(new_obj);
json_object_put(array_obj);
json_object_put(json_obj);
return ret;
}
int read_from_json_file(char *filename)
{
int ret = 0;
json_object *test_obj = NULL;
json_object *tmp_obj = NULL;
json_object *tmp1_obj = NULL;
json_object *tmp2_obj = NULL;
//get json object from file
test_obj = json_object_from_file(filename);
if (!test_obj)
{
printf("Cannot open %s\n", filename);
ret = -1;
goto error;
}
//get null
tmp_obj = json_object_object_get(test_obj, NULL_NULL);
if (tmp_obj)
{
printf("Cannot get %s object\n", NULL_NULL);
ret = -1;
goto error;
}
printf("%s = %s\n", NULL_NULL, "null");
//get boolean
tmp_obj = json_object_object_get(test_obj, BOOL_BOOLEAN);
if (!tmp_obj)
{
printf("Cannot get %s object\n", BOOL_BOOLEAN);
ret = -1;
goto error;
}
printf("%s = %s\n", BOOL_BOOLEAN, ((json_object_get_boolean(tmp_obj))?("TRUE"):("FALSE")));
//get string
tmp_obj = json_object_object_get(test_obj, STR_STRING);
if (!tmp_obj)
{
printf("Cannot get %s object\n", STR_STRING);
ret = -1;
goto error;
}
printf("%s = %s\n", STR_STRING, json_object_get_string(tmp_obj));
//get integer
tmp_obj = json_object_object_get(test_obj, NUM_INTEGER);
if (!tmp_obj)
{
printf("Cannot get %s object\n", NUM_INTEGER);
ret = -1;
goto error;
}
printf("%s = %d\n", NUM_INTEGER, json_object_get_int(tmp_obj));
//get double
tmp_obj = json_object_object_get(test_obj, NUM_DOUBLE);
if (!tmp_obj)
{
printf("Cannot get %s object\n", NUM_DOUBLE);
ret = -1;
goto error;
}
printf("%s = %F\n", NUM_DOUBLE, json_object_get_double(tmp_obj));
//get array
tmp_obj = json_object_object_get(test_obj, ARR_ARRAY);
if (!tmp_obj)
{
printf("Cannot get %s object\n", ARR_ARRAY);
ret = -1;
goto error;
}
//get the length of the array
printf("%s size = %d\n", ARR_ARRAY, json_object_array_length(tmp_obj));
//get the value of array[0]
tmp1_obj = json_object_array_get_idx(tmp_obj, 0);
printf("%s[0] = %s\n", ARR_ARRAY, json_object_get_string(tmp1_obj));
//get the value of array[1]
tmp1_obj = json_object_array_get_idx(tmp_obj, 1);
printf("%s[1] = %s\n", ARR_ARRAY, json_object_get_string(tmp1_obj));
//get the value of array[2]
tmp1_obj = json_object_array_get_idx(tmp_obj, 2);
printf("%s[2] = %s\n", ARR_ARRAY, json_object_get_string(tmp1_obj));
//get object
tmp_obj = json_object_object_get(test_obj, OBJ_OBJECT);
if (!tmp_obj)
{
printf("Cannot get %s object\n", OBJ_OBJECT);
ret = -1;
goto error;
}
//get null within a object
tmp1_obj = json_object_object_get(tmp_obj, NULL_MEMBER_NULL);
if (tmp1_obj)
{
printf("Cannot get %s object\n", NULL_MEMBER_NULL);
ret = -1;
goto error;
}
printf("%s = %s\n", NULL_MEMBER_NULL, "null");
//get boolean within a object
tmp1_obj = json_object_object_get(tmp_obj, BOOL_MEMBER_BOOLEAN);
if (!tmp1_obj)
{
printf("Cannot get %s object\n", BOOL_MEMBER_BOOLEAN);
ret = -1;
goto error;
}
printf("%s = %s\n", BOOL_MEMBER_BOOLEAN, ((json_object_get_boolean(tmp1_obj))?("TRUE"):("FALSE")));
//get string within a object
tmp1_obj = json_object_object_get(tmp_obj, STR_MEMBER_STRING);
if (!tmp1_obj)
{
printf("Cannot get %s object\n", STR_MEMBER_STRING);
ret = -1;
goto error;
}
printf("%s = %s\n", STR_MEMBER_STRING, json_object_get_string(tmp1_obj));
//get integer within a object
tmp1_obj = json_object_object_get(tmp_obj, NUM_MEMBER_INTEGER);
if (!tmp1_obj)
{
printf("Cannot get %s object\n", NUM_MEMBER_INTEGER);
ret = -1;
goto error;
}
printf("%s = %d\n", NUM_MEMBER_INTEGER, json_object_get_int(tmp1_obj));
//get double within a object
tmp1_obj = json_object_object_get(tmp_obj, NUM_MEMBER_DOUBLE);
if (!tmp1_obj)
{
printf("Cannot get %s object\n", NUM_MEMBER_DOUBLE);
ret = -1;
goto error;
}
printf("%s = %F\n", NUM_MEMBER_DOUBLE, json_object_get_double(tmp1_obj));
//get array within a object
tmp1_obj = json_object_object_get(tmp_obj, ARR_MEMBER_ARRAY);
if (!tmp1_obj)
{
printf("Cannot get %s object\n", ARR_MEMBER_ARRAY);
ret = -1;
goto error;
}
//get the length of the array within a object
printf("%s size = %d\n", ARR_MEMBER_ARRAY, json_object_array_length(tmp1_obj));
//get the value of array[0] within a object
tmp2_obj = json_object_array_get_idx(tmp1_obj, 0);
printf("%s[0] = %d\n", ARR_MEMBER_ARRAY, json_object_get_int(tmp2_obj));
//get the value of array[0] within a object
tmp2_obj = json_object_array_get_idx(tmp1_obj, 1);
printf("%s[1] = %d\n", ARR_MEMBER_ARRAY, json_object_get_int(tmp2_obj));
//get the value of array[0] within a object
tmp2_obj = json_object_array_get_idx(tmp1_obj, 2);
printf("%s[2] = %d\n", ARR_MEMBER_ARRAY, json_object_get_int(tmp2_obj));
error:
json_object_put(test_obj);
return ret;
}
int main(int argc, char *argv[])
{
int ret = 0;
ret = write_to_json_file(EXAMPLE_JSON);
if (ret != 0)
printf("Fail to write a json file\n");
ret = read_from_json_file(EXAMPLE_JSON);
if (ret != 0)
printf("Fail to read a json file\n");
return 0;
}
沒有留言:
張貼留言