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Simple and easy-to-use JSON parser in C

#c #programming #json #opensource

This article introduces the JSON parser of the open source C library Melon.

I believe many readers have heard of or even used the cJSON. So this article will compare cJSON and Melon’s JSON component.

Let’s take a look together below.

Encode

Suppose we want to build the following JSON:

{ "name": "Awesome 4K", "resolutions": [ { "width": 1280, "height": 720 }, { "width": 1920, "height": 1080 }, { "width": 3840, "height": 2160 } ] }
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So, let’s first take a look at the cJSON version:

#include <stdio.h> #include <cjson/cJSON.h>  //NOTE: Returns a heap allocated string, you are required to free it after use. char *create_monitor_with_helpers(void) { const unsigned int resolution_numbers[3][2] = { {1280, 720}, {1920, 1080}, {3840, 2160} }; char *string = NULL; cJSON *resolutions = NULL; size_t index = 0; cJSON *monitor = cJSON_CreateObject(); if (cJSON_AddStringToObject(monitor, "name", "Awesome 4K") == NULL) { goto end; } resolutions = cJSON_AddArrayToObject(monitor, "resolutions"); if (resolutions == NULL) { goto end; } for (index = 0; index < (sizeof(resolution_numbers) / (2 * sizeof(int))); ++index) { cJSON *resolution = cJSON_CreateObject(); if (cJSON_AddNumberToObject(resolution, "width", resolution_numbers[index][0]) == NULL) { goto end; } if (cJSON_AddNumberToObject(resolution, "height", resolution_numbers[index][1]) == NULL) { goto end; } cJSON_AddItemToArray(resolutions, resolution); } string = cJSON_Print(monitor); if (string == NULL) { fprintf(stderr, "Failed to print monitor.\n"); } end: cJSON_Delete(monitor); return string; } int main(void) { char *p; p = create_monitor_with_helpers(); printf("%s\n", p); return 0; }
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Next, let’s take a look at the Melon’s:

#include <stdio.h> #include "mln_json.h" #include "mln_log.h"  static mln_string_t *generate(void) { mln_json_t j; mln_string_t *ret; mln_json_init(&j); mln_json_generate(&j, "{s:s,s:[{s:d,s:d},{s:d,s:d},{s:d,s:d}]}", \ "name", "Awesome 4K", "resolutions", "width", 1280, "height", 720, \ "width", 1920, "height", 1080, "width", 3840, "height", 2160); ret = mln_json_encode(&j); mln_json_destroy(&j); return ret; } int main(void) { mln_string_t *p; p = generate(); mln_log(none, "%S\n", p); return 0; }
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Decode

We have the following JSON:

{ "name": "Awesome 4K", "resolutions": [ { "width": 1280, "height": 720 } ] }
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Let's take a look at the decoding, cJSON first:

#include <stdio.h> #include <cjson/cJSON.h>  int supports_full_hd(const char * const monitor) { const cJSON *resolution = NULL; const cJSON *resolutions = NULL; cJSON *monitor_json = cJSON_Parse(monitor); if (monitor_json == NULL) return -1; resolutions = cJSON_GetObjectItemCaseSensitive(monitor_json, "resolutions"); cJSON_ArrayForEach(resolution, resolutions) { cJSON *width = cJSON_GetObjectItemCaseSensitive(resolution, "width"); return width->valuedouble; } cJSON_Delete(monitor_json); return -1; } int main(void) { char p[] = "{\"name\":\"Awesome 4K\",\"resolutions\":[{\"width\":1280,\"height\":720}]}"; int i = supports_full_hd(p); printf("%d\n", i); return 0; }
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Next is the Melon's:

#include <stdio.h> #include "mln_json.h" #include "mln_log.h"  static int handler(mln_json_t *j, void *data) { return (int)mln_json_number_data_get(j); } static int parse(mln_string_t *p) { mln_json_t j; mln_string_t exp = mln_string("resolutions.0.width"); mln_json_decode(p, &j); return mln_json_parse(&j, &exp, handler, NULL); } int main(void) { mln_string_t p = mln_string("{\"name\":\"Awesome 4K\",\"resolutions\":[{\"width\":1280,\"height\":720}]}"); int i = parse(&p); mln_log(none, "%d\n", i); return 0; }
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Write at the end

Melon's JSON component mainly provides the following four functions to facilitate users to encode and decode JSON:

  • mln_json_decode decodes JSON strings into JSON structure nodes
  • mln_json_parse obtains the corresponding JSON sub-node from the decoded JSON structure based on the given expression
  • mln_json_generate builds a JSON structure based on the given format information
  • mln_json_encode generates a JSON string based on the generated JSON structure

Melon's JSON component provides a functional interface that is easy to read and use, making it easier for developers to maintain projects.

Welcome to try the open source C library Melon.

Github：https://github.com/Water-Melon/Melon

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