在 ESP8266 上读取 c 中的 const* 时崩溃

Question

我正在制作一个系统，通过 SoftwareSerial 从 Arduino Uno 读取传感器值并通过 MQTT 发布它。但是，我认为我面临的问题更普遍，我必须承认我是 c 的新手。

我正在读取数据，并将其拆分为在我的程序顶部定义的两个 const* 变量。

当我读回从串行连接解析的已保存“数据”和“主题”变量时，我只会得到垃圾输出，并且通常会导致设备崩溃。

它在 read-from-serial 函数中打印成功，但后面无法正确读取。它与数据的保存方式有关吗？我可以显式地为变量分配一些内存吗？

我使用的是 ESP8266 (ESP07) 芯片，具有较低的波特率和适当的电压供应。它似乎运行良好且稳定。

#include <StringSplitter.h>
#include <PubSubClient.h>
#include <ESP8266WiFi.h>
#include <time.h>

//const char* ssid = "xxxx";
//const char* password =  "xxxx";
const char* ssid = "xxxx";
const char* password =  "xxxx";
const char* mqttServer = "xxxx;
const int mqttPort = xxxx;
const char* mqttUser = "xxxx";
const char* mqttPassword = "xxxx";
int timezone = 1;
int dst = 0;

数据存储在这里:

char* data;
char* topic;
boolean newData = false;
boolean unpublishedData = false;

WiFiClient espClient;
PubSubClient client(espClient);

void setup() {

  Serial.begin(19200);
  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.println("Connecting to WiFi..");
  }
  Serial.println("Connected to the WiFi network");
  configTime(timezone * 3600, dst * 0, "pool.ntp.org", "time.nist.gov");


  client.setServer(mqttServer, mqttPort);
  client.setCallback(callback);

  while (!client.connected()) {
    Serial.println("Connecting to MQTT...");

    if (client.connect("ESP8266Client", mqttUser, mqttPassword )) {

      Serial.println("connected");

    } else {

      Serial.print("failed with state ");
      Serial.print(client.state());
      delay(2000);

    }
    // wait and determine if we have a valid time from the network.
    time_t now = time(nullptr);
    Serial.print("Waiting for network time.");
    while (now <= 1500000000) {
      Serial.print(".");
      delay(300); // allow a few seconds to connect to network time.
      now = time(nullptr);
    }
  }
  Serial.println("");

  time_t now = time(nullptr);
  Serial.println(ctime(&now));

  String datatext = "val: ";
  String timetext = ", time: ";
  String dataToBeSent = "test";
  String timeToBeSent = ctime(&now);

  String publishString = datatext + dataToBeSent + timetext + timeToBeSent;
  Serial.println("Attempting to publish: " + publishString);
  client.publish("trykk/sensor0", (char*) publishString.c_str());
  client.subscribe("trykk/sensor0");

}

void callback(char* topic, byte* payload, unsigned int length) {

  Serial.print("Message arrived in topic: ");
  Serial.println(topic);

  Serial.print("Message:");
  for (int i = 0; i < length; i++) {
    Serial.print((char)payload[i]);
  }

  Serial.println();
  Serial.println("-----------------------");

}

void loop() {
  client.loop();
  recvWithStartEndMarkers();
  showNewData();
  publishReceived();
}

void publishReceived() {
  if (unpublishedData) {
    Serial.println("Hello from inside the publisher loop!");
    time_t now = time(nullptr);
    char* timeNow = ctime(&now);

这里失败了，读取数据:

    char publishText[30]; //TODO: make it JSON
    strcpy( publishText, data );
    strcat( publishText, " " );
    strcat( publishText, timeNow );

    Serial.print("publishText: ");
    Serial.println(publishText);
    Serial.print("topic: "); 
    Serial.println(topic);
    client.publish(topic, publishText);
    client.subscribe(topic);
    unpublishedData = false;
  } else if (!data) {
    Serial.println("No data saved to array.");
  } else if (!topic) {
    Serial.println("No topic saved to array.");
  }
}

void recvWithStartEndMarkers() {
  int numChars = 32;
  char receivedChars[numChars];
  static boolean recvInProgress = false;
  static byte ndx = 0;
  char startMarker = '<';
  char endMarker = '>';
  char rc;

  if (Serial.available() > 0) {
    Serial.println("Hello from inside the receive loop!");
    delay(100);
    while (Serial.available() > 0 && newData == false) {
      rc = Serial.read();
      Serial.println("Reading from data line.");

      if (recvInProgress == true) {
        if (rc != endMarker) {
          receivedChars[ndx] = rc;
          ndx++;
          if (ndx >= numChars) {
            ndx = numChars - 1;
          }
        }
        else {
          Serial.println("Found the end marker.");
          receivedChars[ndx] = '\0'; // terminate the string
          recvInProgress = false;
          ndx = 0;
          newData = true;
          unpublishedData = true;

这部分将正确的值打印回给我:

          //Split the string
          Serial.print("ESP debug: read: ");
          Serial.println(receivedChars);
          const char s[2] = ":";
          *data = strtok(receivedChars, s);
          Serial.print(data);
          Serial.print(" ");
          *topic = strtok(NULL, s);
          Serial.println(topic);
        }
      }

      else if (rc == startMarker) {
        recvInProgress = true;
        Serial.println("Found start marker");
      }
    }
  }
}

//This is gutted as it gave me problems reading the variables
void showNewData() {
  if (newData == true) {
    Serial.print("This just in ... ");
    Serial.print("Topic: ");
    Serial.print("stuff");
    Serial.print(", data: ");
    Serial.println("more stuff");
    newData = false;
  }
}

Answer 1

来自您的代码:

char* data;
...
*data = strtok(receivedChars, s);

strtok 返回一个 char* 但你做 *data = strtok(...) 而 data本身是一个(未初始化的)char *，这是不一致的，并且您有第一个“机会”发生崩溃，因为您在随机地址写入。

如果你没有崩溃并且你的程序可以继续数据不会被自己修改并且保持未初始化状态。

在

strcpy( publishText, data );
...
Serial.print(data);

当您使用 data 作为 char* 执行 Serial.print(data); 和 strcpy( publishText, data ) ; 你从一个随机的(当然是无效的)地址读取，导致你的崩溃。

要更正，只需将 *data = strtok(receivedChars, s); 替换为 data = strtok(receivedChars, s);