在ESP8266上的C中读取const *时崩溃

Question

我正在创建一个系统，该系统通过SoftwareSerial从Arduino Uno读取传感器值，并通过MQTT发布它。但是，我认为所面临的问题更为笼统，我必须承认我是c语言的新手。

我正在读取数据，并将其拆分为程序顶部定义的两个const *变量。

当我读回从串行连接中解析的已保存的“数据”和“主题”变量时，我只会得到垃圾输出，通常会崩溃，从而重启设备。

它可以在read-from-serial函数中成功打印它们，但以后无法正确读取。它与数据的保存方式有关吗？我可以为变量显式分配一些内存吗？

我正在使用ESP8266（ESP07）芯片，其波特率降低且电源电压合适。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);

它在这里失败，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;

这部分将值正确地打印给我：

          //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

从您的代码：

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

strtok返回a，char*但是您*data = strtok(...)在数据本身是a（未初始化）char *时执行此操作，这是不一致的，并且您有第一个“机会”发生崩溃，因为您是在随机地址上写的。

如果您没有崩溃，并且程序可以继续运行，则数据本身不会被修改并且不会被初始化。

在

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

当您使用的数据为char*做Serial.print(data);而strcpy( publishText, data );你从一个随机（当然无效）地址读取，产生你的崩溃。

要纠正，只需替换*data = strtok(receivedChars, s);为data = strtok(receivedChars, s);