geeker/SunnyLand
6
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

nlohmann_json使用方法

Browse Source
This commit is contained in:
Ziyu
2025-06-16 14:44:47 +08:00
parent 2e4935f2df
commit ed38fcee73
2 changed files with 174 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files
assets/save_json.json
+46
View File
@@ -0,0 +1,46 @@
{
"name": "张三 (Zhang San)",
"age": 30,
"height_meters": 1.75,
"isStudent": false,
"email": "zhangsan@example.com",
"middleName": null,
"address": {
"street": "人民路123号 (Renmin Road No. 123)",
"city": "示例市 (Sample City)",
"zipCode": "100000",
"isPrimary": true
},
"hobbies": [
"编程 (Programming)",
"阅读 (Reading)",
"旅行 (Traveling)"
],
"scores": [
95,
88,
72.5
],
"projects": [
{
"projectName": "项目Alpha (Project Alpha)",
"status": "已完成 (Completed)",
"budget": 50000.75,
"isActive": true
},
{
"projectName": "项目Beta (Project Beta)",
"status": "进行中 (In Progress)",
"budget": 120000,
"isActive": true,
"deadline": null
}
],
"metadata": {
"version": 1.2,
"tags": [
"data",
"example"
]
}
}
main.cpp
+128 -11
View File
@@ -6,21 +6,138 @@
#include <glm/glm.hpp>
#include <nlohmann/json.hpp>
#include <spdlog/spdlog.h>
#include <fstream>
int main(int, char**) {
// 设置日志等级，不设置的话默认为 info
spdlog::set_level(spdlog::level::err);
try {
// 1. 载入JSON文件
std::ifstream input_file("assets/json_example.json");
nlohmann::ordered_json json_data = nlohmann::ordered_json::parse(input_file);
input_file.close();
spdlog::info("JSON 成功载入!");
// 不同等级的log
spdlog::trace("最低级别log!");
spdlog::debug("调试信息!");
spdlog::info("你好，世界!");
spdlog::warn("警告!，很可能会出错");
spdlog::error("程序出错啦!");
spdlog::critical("最高级别的log!, 比error还严重!");
// 2. 获取不同类型的数据
// 2.1 字符串 (String)
std::string name = json_data["name"].get<std::string>();
spdlog::info("Name: {}", name);
// 2.2 数字 (Number)
int age = json_data["age"].get<int>();
double height = json_data["height_meters"].get<double>();
spdlog::info("Age: {}, Height: {}", age, height);
// 2.3 布尔值 (Boolean)
bool isStudent = json_data["isStudent"].get<bool>();
spdlog::info("Is Student: {}", isStudent);
// 2.4 null 值
// 检查是否为null
if (json_data["middleName"].is_null()) {
spdlog::info("Middle Name: null");
} else {
spdlog::info("Middle Name: {}", json_data["middleName"].get<std::string>());
}
// 2.5 另外一种方法：使用 .at() 方法访问
std::string email = json_data.at("email").get<std::string>();
spdlog::info("Email: {}", email);
// 3 安全访问的方法
// 3.1 .contains() 检查某个键是否存在，如果不存在则返回 false
if (json_data.contains("email"))
{
std::string email = json_data.at("email").get<std::string>();
spdlog::info("Email: {}", email);
}
if (json_data.contains("nonExistentKey"))
{
spdlog::info("nonExistentKey found!"); // 不会执行
}
else
{
spdlog::info("'nonExistentKey' not found.");
}
// 3.2 .value() 获取一个可能存在的键，如果不存在则返回指定默认值（第二个参数）
std::string optional_value = json_data.value("optionalKey", "default_string_value");
int optional_int = json_data.value("optionalNumber", 42);
spdlog::info("Optional Key (string): {}", optional_value);
spdlog::info("Optional Key (int): {}", optional_int);
// 4 对象 (Object)
nlohmann::ordered_json address_obj = json_data["address"];
std::string street = address_obj["street"].get<std::string>();
std::string city = address_obj.value("city", "Unknown City"); // 使用 .value() 提供默认值
bool isPrimaryAddr = address_obj.value("isPrimary", false); // 访问对象内的布尔值
spdlog::info("Address: {}, {}", street, city);
spdlog::info("Is Primary Address: {}", isPrimaryAddr);
// 5.1 数组 (Array) - 字符串数组
spdlog::info("Hobbies:");
nlohmann::ordered_json hobbies_array = json_data["hobbies"];
for (const auto &hobby : hobbies_array)
{
spdlog::info(" - {}", hobby.get<std::string>());
}
// 5.2 数组 (Array) - 数字数组
spdlog::info("Scores:");
for (const auto &score_item : json_data["scores"])
{
if (score_item.is_number_integer())
{
spdlog::info(" - {} (integer)", score_item.get<int>());
}
else if (score_item.is_number_float())
{
spdlog::info(" - {} (float)", score_item.get<double>());
}
}
// 5.3 数组 (Array) - 对象数组
spdlog::info("Projects:");
nlohmann::ordered_json projects_array = json_data["projects"];
for (const auto &project : projects_array)
{
std::string projectName = project["projectName"].get<std::string>();
std::string status = project["status"].get<std::string>();
double budget = project.value("budget", 0.0); // 使用 value 获取，若不存在则为0.0
bool isActive = project.value("isActive", false);
spdlog::info(" ProjectName: {}", projectName);
spdlog::info(" Status: {}", status);
spdlog::info(" Budget: {}", budget);
spdlog::info(" Is Active: {}", isActive);
if (project.contains("deadline") && project["deadline"].is_null())
{
spdlog::info(" Deadline: null");
}
else if (project.contains("deadline"))
{
spdlog::info(" Deadline: {}", project["deadline"].get<std::string>());
}
spdlog::info("--------------------------------");
}
// 5.4 直接访问更深层嵌套的对象和数组
double metadata_version = json_data["metadata"]["version"].get<double>();
spdlog::info("Metadata Version: {}", metadata_version);
spdlog::info("Metadata Tags:");
for (const auto &tag_json : json_data["metadata"]["tags"])
{
std::string tag = tag_json.get<std::string>();
spdlog::info(" - {}", tag);
}
// 6 将json数据保存为文件
std::ofstream output_file("assets/save_json.json");
output_file << json_data.dump(4); // 使用 dump(4) 进行格式化输出，缩进为4个空格
output_file.close();
spdlog::info("JSON 数据已保存到文件 assets/save_json.json");
} catch (const std::exception &e) {
spdlog::error("Exception: {}", e.what());
// return EXIT_FAILURE;
}
// 格式化输出
spdlog::info("日志格式化输出: {} {} {}", 1, "hello", 3.14);
return 0;
}