void *__symbol_get(const char *symbol)可以使用吗

这个函数的使用需要看具体的情况。一般情况下，这个函数是在动态链接库中使用的，用于获取指定符号的地址。如果你的程序中需要动态加载一个共享库，并且需要调用该库中的某个函数或变量，可以使用该函数动态获取该函数或变量在内存中的地址。但是，需要注意的是，该函数是非标准的，不同的操作系统和编译器可能会有不同的实现方式，因此需要仔细检查相关文档和代码实现。同时，使用该函数需要非常小心，因为错误的使用可能会导致内存泄漏、缓冲区溢出等问题。

相关问题

使用Arduino +lvgl+esp32+tft_espi写一个网络天气时钟

很高兴回答你的问题，以下是使用Arduino、lvgl、esp32和tft_espi的示例代码实现网络天气时钟的方法：

#include <Arduino.h>
#include <TFT_eSPI.h>
#include <lvgl.h>
#include <WiFi.h>
#include <ArduinoJson.h>
#include <time.h>

#define WIFI_SSID "your_wifi_ssid"
#define WIFI_PASS "your_wifi_password"
#define OPENWEATHERMAP_APIKEY "your_openweathermap_api_key"

TFT_eSPI tft = TFT_eSPI(135, 240); // 设置 TFT 屏幕的大小
lv_obj_t * label_temperature, * label_temperature_symbol, * label_weather_description, * label_city_name, * label_clock;

void get_weather_data(String & temperature, String & weather_description, String & city_name) {
  WiFiClient client;
  if (!client.connect("api.openweathermap.org", 80)) {
    Serial.println("connection failed!");
    return;
  }

  String url = "/data/2.5/weather?q=Shenzhen,CN&appid=" OPENWEATHERMAP_APIKEY "&units=metric";

  client.print(String("GET ") + url + " HTTP/1.1\r\n" +
               "Host: api.openweathermap.org\r\n" +
               "Connection: close\r\n\r\n");

  String response = "";
  while (client.connected()) {
    String line = client.readStringUntil('\n');
    if (line == "\r") {
      break;
    }
  }
  while (client.available()) {
    response += (char)client.read();
  }

  const int capacity = JSON_OBJECT_SIZE(4) + 100;
  DynamicJsonDocument doc(capacity);
  deserializeJson(doc, response);
  JsonObject main = doc["main"];
  temperature = main["temp"].as<String>();
  JsonArray weather = doc["weather"];
  weather_description = weather[0]["description"].as<String>();
  city_name = doc["name"].as<String>();
}

void get_time_string(String & time_string) {
  time_t now;
  struct tm timeinfo;
  time(&now);
  localtime_r(&now, &timeinfo);
  char strftime_buf[64];
  strftime(strftime_buf, sizeof(strftime_buf), "%H:%M", &timeinfo);
  time_string = strftime_buf;
}

void setup() {
  Serial.begin(115200);

  lv_init();

  tft.init();
  tft.setRotation(3);
  tft.fillScreen(TFT_BLACK);

  lvgl_driver_init(&tft);
  lv_disp_drv_t disp_drv;
  lv_disp_drv_init(&disp_drv);
  disp_drv.buffer = &lvgl_buffer;
  disp_drv.flush_cb = lvgl_flush;
  lv_disp_drv_register(&disp_drv);

  lv_theme_t * theme = lv_theme_material_init(210, NULL);
  lv_theme_set_current(theme);

  label_temperature = lv_label_create(lv_scr_act(), NULL);
  lv_label_set_text(label_temperature, "temperature");
  lv_obj_align(label_temperature, NULL, LV_ALIGN_CENTER, 0, -40);
  label_temperature_symbol = lv_label_create(lv_scr_act(), NULL);
  lv_label_set_text(label_temperature_symbol, "°C");
  lv_obj_set_pos(label_temperature_symbol, lv_obj_get_x(label_temperature) + lv_obj_get_width(label_temperature), lv_obj_get_y(label_temperature));
  label_weather_description = lv_label_create(lv_scr_act(), NULL);
  lv_label_set_text(label_weather_description, "weather_description");
  lv_obj_align(label_weather_description, NULL, LV_ALIGN_CENTER, 0, 0);
  label_city_name = lv_label_create(lv_scr_act(), NULL);
  lv_label_set_text(label_city_name, "city_name");
  lv_obj_align(label_city_name, NULL, LV_ALIGN_CENTER, 0, 40);
  label_clock = lv_label_create(lv_scr_act(), NULL);
  lv_label_set_text(label_clock, "clock");
  lv_obj_align(label_clock, NULL, LV_ALIGN_CENTER, 0, 80);

  lv_task_create([](lv_task_t * task) {
    String temperature;
    String weather_description;
    String city_name;
    get_weather_data(temperature, weather_description, city_name);
    lv_label_set_text(label_temperature, temperature.c_str());
    lv_label_set_text(label_weather_description, weather_description.c_str());
    lv_label_set_text(label_city_name, city_name.c_str());
  }, 5000, LV_TASK_PRIO_LOW, NULL);

  lv_task_create([](lv_task_t * task) {
    String time_string;
    get_time_string(time_string);
    lv_label_set_text(label_clock, time_string.c_str());
  }, 1000, LV_TASK_PRIO_MID, NULL);

  WiFi.begin(WIFI_SSID, WIFI_PASS);
  while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
  }

  Serial.println("setup complete!");
}

void loop() {
  lv_task_handler();
  delay(1);
}

该代码使用了 OpenWeatherMap API 获取深圳的当前天气数据，在屏幕上输出温度、天气描述和城市名称，通过 `lv_task_create` 函数设置定时任务每 5 秒钟更新一次天气信息和每秒钟更新一次当前时间，是一个简单而实用的网络天气时钟的实现方式。

注：这里使用的API Key只是做演示，请勿用于商业用途，如有需要请自行注册。

#include <stdio.h> #include <iostream> #include <chrono> #include <thread> #include <DjiRtspImageSource.h> #define STB_IMAGE_WRITE_IMPLEMENTATION #include "stb_image_write.h" static inline int64_t now() { return std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::system_clock::now().time_since_epoch()).count(); } static int write_data_to_file(const char* name, uint8_t* data, int size) { FILE* fd = fopen(name, "wb"); if(fd) { int w = (int)fwrite(data, 1, size, fd); fclose(fd); return w; } else { return -1; } } char rtsp_url = "rtsp://192.168.42.142:8554/live"; int main(int argc, char** argv) { if(argc < 1) return -1; if(argc == 1) { std::cout << "Usage : " << argv[0] << " <url>" << std::endl; return -1; } int64_t ts = now(); DjiRtspImageSource service(rtsp_url); service.setImageCallback(nullptr, [&ts](void* handler, uint8_t* frmdata, int frmsize, int width, int height, int pixfmt) -> void { printf("Image %d@%p -- %dx%d -- %d\n", frmsize, frmdata, width, height, pixfmt); if(frmdata) { int64_t t = now(); if(t - ts > 1000) { ts = t; char name[64]; static int counter = 0; sprintf(name, "pictures/%dx%d-%d_%d.jpg", width, height, pixfmt, ++counter); if(pixfmt == 5) stbi_write_jpg(name, width, height, 3, frmdata, 80); } } }); service.start(); for(;;) //for(int i=0; i<30; i++) { std::this_thread::sleep_for(std::chrono::milliseconds(1000)); } service.stop(); std::cout << "done." << std::endl; return 0; } 利用上述代码实现提取并解码二维码的信息，并将解码结果保存到tta文件夹下保存为文件名为 list_of_goods,给出c++源码

以下是使用 C++ 代码从图像中提取和解码二维码信息，并将解码结果保存到名为 "list_of_goods.txt" 的文件中：

#include <stdio.h>
#include <iostream>
#include <chrono>
#include <thread>
#include <DjiRtspImageSource.h>
#include <zbar.h>

#define STB_IMAGE_WRITE_IMPLEMENTATION
#include "stb_image_write.h"

using namespace std;
using namespace zbar;

static inline int64_t now()
{
    return chrono::duration_cast<chrono::milliseconds>(chrono::system_clock::now().time_since_epoch()).count();
}

static int write_data_to_file(const char* name, uint8_t* data, int size)
{
    FILE* fd = fopen(name, "wb");
    if(fd)
    {
        int w = (int)fwrite(data, 1, size, fd);
        fclose(fd);
        return w;
    }
    else
    {
        return -1;
    }
}

void save_qr_code_data(const char* data)
{
    FILE* file = fopen("tta/list_of_goods.txt", "a");
    if (file)
    {
        fprintf(file, "%s\n", data);
        fclose(file);
    }
}

char rtsp_url[] = "rtsp://192.168.42.142:8554/live";

int main(int argc, char** argv)
{
    if(argc < 1) return -1;
    if(argc == 1) 
    {
        cout << "Usage : " << argv[0] << " <url>" << endl;
        return -1;
    }
    int64_t ts = now();

    DjiRtspImageSource service(rtsp_url);
    service.setImageCallback(nullptr, [&ts](void* handler, uint8_t* frmdata, int frmsize, int width, int height, int pixfmt) -> void {
        printf("Image %d@%p  --  %dx%d -- %d\n", frmsize, frmdata, width, height, pixfmt);
        if(frmdata)
        {
            int64_t t = now();
            if(t - ts > 1000)
            {
                ts = t;
                char name[64];
                static int counter = 0;
                sprintf(name, "pictures/%dx%d-%d_%d.jpg", width, height, pixfmt, ++counter);
                if(pixfmt == 5)
                {
                    stbi_write_jpg(name, width, height, 3, frmdata, 80);

                    // Decode QR code
                    ImageScanner scanner;
                    scanner.set_config(ZBAR_NONE, ZBAR_CFG_ENABLE, 1);
                    Image image(width, height, "Y800", frmdata, width * height);
                    int n = scanner.scan(image);
                    for (Image::SymbolIterator symbol = image.symbol_begin(); symbol != image.symbol_end(); ++symbol)
                    {
                        cout << "QR code data: " << symbol->get_data() << endl;
                        save_qr_code_data(symbol->get_data().c_str());
                    }
                }
            }
        }
    });
    service.start();
    for(;;)
    //for(int i=0; i<30; i++)
    {
        this_thread::sleep_for(chrono::milliseconds(1000));
    }
    service.stop();
    cout << "done." << endl;
    return 0;
}

注意，上述代码使用了 `zbar` 库来进行二维码解码。确保在编译和运行之前已经安装了该库，并根据需要修改保存文件的路径。同时，需要确保 "tta" 文件夹已经存在，以便保存解码结果。