本文介绍开源C语言库Melon(https://github.com/Water-Melon/Melon)的JSON解析器。 相信很多读者都听说过甚至使用过cJSON开源库。那么本文就拿cJSON与Melon的JSON组件进行对比。 下面我们就来一起看一看。 编码Encode假设我们要构建如下JSON： { "name": "Awesome 4K", "resolutions": [ { "width": 1280, "height": 720 }, { "width": 1920, "height": 1080 }, { "width": 3840, "height": 2160 } ]}那么，我们先看一下cJSON的构建代码： #include #include //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;}下面，我们一起看下使用Melon的JSON组件的代码： #include #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;}解码Decode假设我们有如下JSON： { "name": "Awesome 4K", "resolutions": [ { "width": 1280, "height": 720 } ]}下面一起来看下解码，还是先上cJSON的代码： #include #include /* return 1 if the monitor supports full hd, 0 otherwise */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;}接下来是Melon的JSON组件的解码代码： #include #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;}结语Melon的JSON组件主要提供了如下四个函数来便于使用者构建和解析JSON： mln_json_decode解码JSON字符串为JSON结构体结点mln_json_parse从解码的JSON结构体中，根据给定表达式，获取对应的JSON子结点mln_json_generate根据给定的格式信息构建JSON结构体mln_json_encode根据生成的JSON结构体生成JSON字符串Melon的JSON组件提供了易于阅读和使用的函数接口，更易于开发者对项目的维护。 欢迎大家来试用开源C语言库Melon。 Github：https://github.com/Water-Melon/Melon