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c语言-json开源库cJSON的使用

作者：我家小花儿 | 2024-04-21 02:32:42

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json开源代码c语言

一、cJSON的介绍

    cJSON是一个开源的JSON解析器，用于解析JSON数据。它是由纯C语言实现，因此跨平台性好，移植简单。

下载地址：

  1. https://github.com/DaveGamble/cJSON.git
  2. https://gitee.com/du-yueqiang/cJSON?_from=gitee_search

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二、移植方法

    cJSON只有一个cjson.c和cjson.h文件，可以很方便地集成到其他项目中。cJSON支持将JSON数据解析为cJSON对象，也支持将cJSON对象转换为JSON数据。cJSON的使用非常简单，只需要包含cjson.h头文件，然后调用相应的API即可完成JSON数据的解析和生成。

三、测试代码

  1. //根据官方代码修改，创建json格式数据（字符串、整形、数组）
  2. //增加了json数据解析功能
  3.  
  4.  
  5. #include <stdio.h>
  6. #include <stdlib.h>
  7. #include <string.h>
  8. #include "cJSON.h"
  9.  
  10.  
  11. /* Used by some code below as an example datatype. */
  12. struct record
  13. {
  14.     const char *precision;
  15.     double lat;
  16.     double lon;
  17.     const char *address;
  18.     const char *city;
  19.     const char *state;
  20.     const char *zip;
  21.     const char *country;
  22. };
  23.  
  24.  
  25.  
  26.  
  27. /* Create a bunch of objects as demonstration. */
  28. static int print_preallocated(cJSON *root)
  29. {
  30.     /* declarations */
  31.     char *out = NULL;
  32.     char *buf = NULL;
  33.     char *buf_fail = NULL;
  34.     size_t len = 0;
  35.     size_t len_fail = 0;
  36.  
  37.  
  38.     /* formatted print */
  39.     out = cJSON_Print(root);
  40.  
  41.  
  42.     /* create buffer to succeed */
  43.     /* the extra 5 bytes are because of inaccuracies when reserving memory */
  44.     len = strlen(out) + 5;
  45.     buf = (char*)malloc(len);
  46.     if (buf == NULL)
  47.     {
  48.         printf("Failed to allocate memory.\n");
  49.         exit(1);
  50.     }
  51.  
  52.  
  53.     /* create buffer to fail */
  54.     len_fail = strlen(out);
  55.     buf_fail = (char*)malloc(len_fail);
  56.     if (buf_fail == NULL)
  57.     {
  58.         printf("Failed to allocate memory.\n");
  59.         exit(1);
  60.     }
  61.  
  62.  
  63.     /* Print to buffer */
  64.     if (!cJSON_PrintPreallocated(root, buf, (int)len, 1)) {
  65.         printf("cJSON_PrintPreallocated failed!\n");
  66.         if (strcmp(out, buf) != 0) {
  67.             printf("cJSON_PrintPreallocated not the same as cJSON_Print!\n");
  68.             printf("cJSON_Print result:\n%s\n", out);
  69.             printf("cJSON_PrintPreallocated result:\n%s\n", buf);
  70.         }
  71.         free(out);
  72.         free(buf_fail);
  73.         free(buf);
  74.         return -1;
  75.     }
  76.  
  77.  
  78.     /* success */
  79.     printf("%s\n", buf);
  80.  
  81.  
  82.     /* force it to fail */
  83.     if (cJSON_PrintPreallocated(root, buf_fail, (int)len_fail, 1)) {
  84.         printf("cJSON_PrintPreallocated failed to show error with insufficient memory!\n");
  85.         printf("cJSON_Print result:\n%s\n", out);
  86.         printf("cJSON_PrintPreallocated result:\n%s\n", buf_fail);
  87.         free(out);
  88.         free(buf_fail);
  89.         free(buf);
  90.         return -1;
  91.     }
  92.  
  93.  
  94.     free(out);
  95.     free(buf_fail);
  96.     free(buf);
  97.     return 0;
  98. }
  99.  
  100.  
  101. /* Create a bunch of objects as demonstration. */
  102. static void create_objects(void)
  103. {
  104.     /* declare a few. */
  105.     cJSON *root = NULL;
  106.     cJSON *fmt = NULL;
  107.     cJSON *img = NULL;
  108.     cJSON *thm = NULL;
  109.     cJSON *fld = NULL;
  110.     int i = 0;
  111.     int n;
  112.  
  113.  
  114.     /* Our "days of the week" array: */
  115.     const char *strings[7] =
  116.     {
  117.         "Sunday",
  118.         "Monday",
  119.         "Tuesday",
  120.         "Wednesday",
  121.         "Thursday",
  122.         "Friday",
  123.         "Saturday"
  124.     };
  125.     /* Our matrix: */
  126.     int numbers[3][3] =
  127.     {
  128.         {0, -1, 0},
  129.         {1, 0, 0},
  130.         {0 ,0, 1}
  131.     };
  132.     /* Our "gallery" item: */
  133.     int ids[4] = { 116, 943, 234, 38793 };
  134.     /* Our array of "records": */
  135.     struct record fields[2] =
  136.     {
  137.         {
  138.             "zip",
  139.             37.7668,
  140.             -1.223959e+2,
  141.             "",
  142.             "SAN FRANCISCO",
  143.             "CA",
  144.             "94107",
  145.             "US"
  146.         },
  147.         {
  148.             "zip",
  149.             37.371991,
  150.             -1.22026e+2,
  151.             "",
  152.             "SUNNYVALE",
  153.             "CA",
  154.             "94085",
  155.             "US"
  156.         }
  157.     };
  158.     volatile double zero = 0.0;
  159.  
  160.  
  161.     /* Here we construct some JSON standards, from the JSON site. */
  162.  
  163.  
  164.     /* Our "Video" datatype: */
  165.     root = cJSON_CreateObject();
  166.     cJSON_AddItemToObject(root, "name", cJSON_CreateString("Jack (\"Bee\") Nimble"));
  167.     cJSON_AddItemToObject(root, "format", fmt = cJSON_CreateObject());
  168.     cJSON_AddStringToObject(fmt, "type", "rect");
  169.     cJSON_AddNumberToObject(fmt, "width", 1920);
  170.     cJSON_AddNumberToObject(fmt, "height", 1080);
  171.     cJSON_AddFalseToObject (fmt, "interlace");
  172.     cJSON_AddNumberToObject(fmt, "frame rate", 24);
  173.  
  174.  
  175.     /* Print to text */
  176.     if (print_preallocated(root) != 0) {
  177.         cJSON_Delete(root);
  178.         exit(EXIT_FAILURE);
  179.     }
  180.  
  181.  
  182.     cJSON *name=cJSON_GetObjectItem(root,"name");
  183.     if (cJSON_IsString(name) && (name->valuestring != NULL))
  184.     {
  185.         printf("name is \"%s\"\n", name->valuestring);
  186.     }
  187.  
  188.  
  189.     cJSON *format=cJSON_GetObjectItem(root,"format");
  190.     if (cJSON_IsObject(format) && (format != NULL))
  191.     {
  192.         if (print_preallocated(format) != 0) 
  193.         {
  194.             cJSON_Delete(root);
  195.             exit(EXIT_FAILURE);
  196.         }
  197.         cJSON *type=cJSON_GetObjectItem(format,"type");
  198.         if (cJSON_IsString(type) && (type->valuestring != NULL))
  199.         {
  200.             printf("type is \"%s\"\n", type->valuestring);
  201.         }
  202.         cJSON *width=cJSON_GetObjectItem(format,"width");
  203.         if (cJSON_IsNumber(width))
  204.         {
  205.             printf("width is %d\n", width->valueint);
  206.         }
  207.         cJSON *interlace=cJSON_GetObjectItem(format,"interlace");
  208.         if (cJSON_IsBool(interlace))
  209.         {
  210.             printf("interlace is %d\n", interlace->valueint);
  211.         }
  212.  
  213.  
  214.     }
  215.  
  216.  
  217.     cJSON_Delete(root);
  218.  
  219.  
  220.     /* Our "days of the week" array: */
  221.     root = cJSON_CreateStringArray(strings, 7);
  222.  
  223.  
  224.     if (print_preallocated(root) != 0) {
  225.         cJSON_Delete(root);
  226.         exit(EXIT_FAILURE);
  227.     }
  228.  
  229.  
  230.     n=cJSON_GetArraySize(root);
  231.     cJSON *day;
  232.     for(i=0;i<n;i++)
  233.     {
  234.         day=cJSON_GetArrayItem(root,i);
  235.         if (cJSON_IsString(day) && (day->valuestring != NULL))
  236.         {
  237.             printf("day is \"%s\"\n", day->valuestring);
  238.         }
  239.     }
  240.  
  241.  
  242.     cJSON_Delete(root);
  243.  
  244.  
  245.     /* Our matrix: */
  246.     root = cJSON_CreateArray();
  247.     for (i = 0; i < 3; i++)
  248.     {
  249.         cJSON_AddItemToArray(root, cJSON_CreateIntArray(numbers[i], 3));
  250.     }
  251.  
  252.  
  253.     /* cJSON_ReplaceItemInArray(root, 1, cJSON_CreateString("Replacement")); */
  254.  
  255.  
  256.     if (print_preallocated(root) != 0) {
  257.         cJSON_Delete(root);
  258.         exit(EXIT_FAILURE);
  259.     }
  260.  
  261.  
  262.     n=cJSON_GetArraySize(root);
  263.     cJSON *num;
  264.     for(i=0;i<n;i++)
  265.     {
  266.  
  267.  
  268.         num=cJSON_GetArrayItem(root,i);
  269.         int m=cJSON_GetArraySize(num);
  270.         for(int k=0;k<m;k++)
  271.         {
  272.             cJSON *j=cJSON_GetArrayItem(num,k);
  273.             if (cJSON_IsNumber(j) )
  274.             {
  275.                 printf("day is %d\n", j->valueint);
  276.             }
  277.         }
  278.         
  279.     }
  280.  
  281.  
  282.     cJSON_Delete(root);
  283.  
  284.  
  285.     /* Our "gallery" item: */
  286.     root = cJSON_CreateObject();
  287.     cJSON_AddItemToObject(root, "Image", img = cJSON_CreateObject());
  288.     cJSON_AddNumberToObject(img, "Width", 800);
  289.     cJSON_AddNumberToObject(img, "Height", 600);
  290.     cJSON_AddStringToObject(img, "Title", "View from 15th Floor");
  291.     cJSON_AddItemToObject(img, "Thumbnail", thm = cJSON_CreateObject());
  292.     cJSON_AddStringToObject(thm, "Url", "http:/*www.example.com/image/481989943");
  293.     cJSON_AddNumberToObject(thm, "Height", 125);
  294.     cJSON_AddStringToObject(thm, "Width", "100");
  295.     cJSON_AddItemToObject(img, "IDs", cJSON_CreateIntArray(ids, 4));
  296.  
  297.  
  298.     if (print_preallocated(root) != 0) {
  299.         cJSON_Delete(root);
  300.         exit(EXIT_FAILURE);
  301.     }
  302.     cJSON_Delete(root);
  303.  
  304.  
  305.     /* Our array of "records": */
  306.     root = cJSON_CreateArray();
  307.     for (i = 0; i < 2; i++)
  308.     {
  309.         cJSON_AddItemToArray(root, fld = cJSON_CreateObject());
  310.         cJSON_AddStringToObject(fld, "precision", fields[i].precision);
  311.         cJSON_AddNumberToObject(fld, "Latitude", fields[i].lat);
  312.         cJSON_AddNumberToObject(fld, "Longitude", fields[i].lon);
  313.         cJSON_AddStringToObject(fld, "Address", fields[i].address);
  314.         cJSON_AddStringToObject(fld, "City", fields[i].city);
  315.         cJSON_AddStringToObject(fld, "State", fields[i].state);
  316.         cJSON_AddStringToObject(fld, "Zip", fields[i].zip);
  317.         cJSON_AddStringToObject(fld, "Country", fields[i].country);
  318.     }
  319.  
  320.  
  321.     /* cJSON_ReplaceItemInObject(cJSON_GetArrayItem(root, 1), "City", cJSON_CreateIntArray(ids, 4)); */
  322.  
  323.  
  324.     if (print_preallocated(root) != 0) {
  325.         cJSON_Delete(root);
  326.         exit(EXIT_FAILURE);
  327.     }
  328.     cJSON_Delete(root);
  329.  
  330.  
  331.     root = cJSON_CreateObject();
  332.     cJSON_AddNumberToObject(root, "number", 1.0 / zero);
  333.  
  334.  
  335.     if (print_preallocated(root) != 0) {
  336.         cJSON_Delete(root);
  337.         exit(EXIT_FAILURE);
  338.     }
  339.     cJSON_Delete(root);
  340. }
  341.  
  342.  
  343. int CJSON_CDECL main(void)
  344. {
  345.     /* print the version */
  346.     printf("Version: %s\n", cJSON_Version());
  347.  
  348.  
  349.     /* Now some samplecode for building objects concisely: */
  350.     create_objects();
  351.  
  352.  
  353.     return 0;
  354. }

四、实验结果

执行之后，打印如下信息

  1. Version: 1.7.16
  2. {
  3.   "name":  "Jack (\"Bee\") Nimble",
  4.   "format":  {
  5.     "type":  "rect",
  6.     "width":  1920,
  7.     "height":  1080,
  8.     "interlace":  false,
  9.     "frame rate":  24
  10.   }
  11. }
  12. name is "Jack ("Bee") Nimble"
  13. {
  14.   "type":  "rect",
  15.   "width":  1920,
  16.   "height":  1080,
  17.   "interlace":  false,
  18.   "frame rate":  24
  19. }
  20. type is "rect"
  21. width is 1920
  22. interlace is 0
  23. ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"]
  24. day is "Sunday"
  25. day is "Monday"
  26. day is "Tuesday"
  27. day is "Wednesday"
  28. day is "Thursday"
  29. day is "Friday"
  30. day is "Saturday"
  31. [[0, -1, 0], [1, 0, 0], [0, 0, 1]]
  32. day is 0
  33. day is -1
  34. day is 0
  35. day is 1
  36. day is 0
  37. day is 0
  38. day is 0
  39. day is 0
  40. day is 1
  41. {
  42.   "Image":  {
  43.     "Width":  800,
  44.     "Height":  600,
  45.     "Title":  "View from 15th Floor",
  46.     "Thumbnail":  {
  47.       "Url":  "http:/*www.example.com/image/481989943",
  48.       "Height":  125,
  49.       "Width":  "100"
  50.     },
  51.     "IDs":  [116, 943, 234, 38793]
  52.   }
  53. }
  54. [{
  55.     "precision":  "zip",
  56.     "Latitude":  37.7668,
  57.     "Longitude":  -122.3959,
  58.     "Address":  "",
  59.     "City":  "SAN FRANCISCO",
  60.     "State":  "CA",
  61.     "Zip":  "94107",
  62.     "Country":  "US"
  63.   }, {
  64.     "precision":  "zip",
  65.     "Latitude":  37.371991,
  66.     "Longitude":  -122.026,
  67.     "Address":  "",
  68.     "City":  "SUNNYVALE",
  69.     "State":  "CA",
  70.     "Zip":  "94085",
  71.     "Country":  "US"
  72.   }]
  73. {
  74.   "number":  null
  75. }

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