c - C语言中的分配

Question

我正在将 XDK 博世传感器用于一个用 C 语言编程的项目。这个想法是 XDK 应该能够连接到另一个网络。 SSID 和密码通过 MQTT 发送。初始化时就可以将 XDK 连接到网络。为了接收 MQTT 消息，使用了下面所示的函数，该函数部分由 Bosch Guides 改编。每当收到 MQTT 消息时，就会执行此函数。

• 目标:连接到新的 Wifi 网络

• 我收到的消息始终如下所示:IP_Address/SSID/Password/ 例如192.155.125.146/TestSSID/TestPassword/

• 已测试:函数本身正确接收内容

• 已测试:CountNumberItemsPwd、CountNumberItemsSSID 和 CountNumberItemsIp 可以正确计算 Pwd、SSID 和 IP 地址的字符数

• 对数组 arraySSID、arrayPW 和 arrayIp 使用 printf 显示正确的内容

• 假设问题:传递给将 XDK 连接到新网络的函数的字符数组的大小似乎需要正确调整大小。我尝试使用超大的字符数组但没有成功。因此，我目前正在尝试借助 alloc 来解决该问题。不幸的是，我无法让它工作，也找不到我使用 alloc 做错了什么。

          #define COMMON_BUFFER_SIZE 255
          char MQTT_BROKER_HOST[] =   "192.111.111.111";
          char message_received [COMMON_BUFFER_SIZE];
  
  
          /**
           * @brief Event handler for incoming publish MQTT data
           *
           * @param[in] publishData
           * Event Data for publish
           */
          static void HandleEventIncomingPublish(
                  MqttPublishData_T publishData)
          {
              char published_topic_buffer[COMMON_BUFFER_SIZE];
              char published_data_buffer[COMMON_BUFFER_SIZE];
              static int incoming_message_count = 0;
  
              //storing topic and incoming data
              strncpy(published_data_buffer, (const char *)publishData.payload, sizeof(published_data_buffer));
              strncpy(published_topic_buffer, publishData.topic.start, sizeof(published_topic_buffer));
  
  
              //If the message differs from the one received before, connect to new network
              if (message_received != published_data_buffer)
              {
                  //Store message in message_received
                  strcpy(message_sent, published_data_buffer);
  
                  //For While-Loop
                  int counterForArray = 0;
  
                  //For writing content into correct arrays
                  int BooleanForIP = 0;
                  int BooleanForPw = 0;
                  int BooleanForSSID = 0;
  
                  int CountCycles = 0; //For Array Access
  
                  //Counting of how many items IP Address,  SSID and Password consist of
                  int CountNumberItemsIp = 0;
                  int CountNumberItemsPW = 0;
                  int CountNumberItemsSSID = 0;
  
                  //Buffer Arrays
                  char IP_new[20] = "";
                  char PW_new[50] = "";
                  char SSID_new[25] = "";
  
  
                  while (counterForArray < COMMON_BUFFER_SIZE)
                  {
                          //Check if IP Address has been successfully received
                          if (message_received[counterForArray] == '/' && BooleanForIP == 0 && BooleanForSSID == 0 && BooleanForPw == 0)
                          {
                              BooleanForIP = 1;
                              CountNumberItemsIp = CountCycles;
                              CountCycles = 0;
  
                          }
                           //Checking if SSID has been successfully received
                          else if (message_received[counterForArray] == '/' && BooleanForIP == 1 && BooleanForSSID == 0 && BooleanForPw == 0)
                          {
  
                              BooleanForSSID = 1;
                              CountNumberItemsSSID  = CountCycles;
                              CountCycles = 0;
  
                              printf("Stage 2 reached \n");
                          }
  
                          //Checking if Password has been successfully received
                          else if (message_received[counterForArray] == '/' && BooleanForIP == 1 && BooleanForSSID == 1 && BooleanForPw == 0)
                              {
                                  BooleanForPw = 1;
                                  CountNumberItemsPW = CountCycles;
                                  CountCycles = 0;
                             }
  
  
  
                          if (BooleanForIP == 0 && BooleanForPw == 0 && BooleanForSSID == 0)
                          {
                              IP_new[CountCycles] = message_received[counterForArray];
                                     CountCycles = CountCycles + 1;
                          }
  
                          else if (BooleanForIP == 1 && BooleanForPw == 0 && BooleanForSSID == 0 && message_received[counterForArray] != '/')
                          {
                              SSID_new[CountCycles] = message_received[counterForArray];
                                  CountCycles = CountCycles + 1;
                          }
  
                          else if (BooleanForIP == 1 && BooleanForPw == 0 && BooleanForSSID == 1 && message_received[counterForArray] != '/')
                              {
                                  PW_new[CountCycles] = message_received[counterForArray];
                                  CountCycles = CountCycles + 1;
                             }
  
                      counterForArray = counterForArray + 1;
                  }
  
                  //Dynamic memory
                  char *arraySSID;
                                  arraySSID = (char*)calloc(CountNumberItemsSSID, sizeof(char));
  
                   char *arrayIP;
                  arrayIP = (char*)calloc(CountNumberItemsIp, sizeof(char));
  
                           char *arrayPW;
                          arrayPW = (char*)calloc(CountNumberItemsPW, sizeof(char));
  
                          //Copying content
  
          int SSID = 0;
          while (SSID <= CountNumberItemsSSID)
          {
              arraySSID[SSID] = SSID_new[SSID];
              SSID = SSID + 1;
          }
  
          int PW = 0;
  
          while (PW <= CountNumberItemsPW)
          {
              arrayPW[PW] = PW_new[PW];
              PW = PW + 1;
          }
  
          int IP = 0;
          while (IP <= CountNumberItemsIp)
         {
                 arrayIP[IP] = IP_new[IP];
                 IP = IP + 1;
         }
  
                  //Disconnecting from old Wifi
                  //Functions provided by Bosch
  
                  Retcode_T retStatusDisconnect = (Retcode_T) WlanConnect_Disconnect(0);
                  retcode_t DisconnectMQTT = Disconnect();
  
                  Retcode_T connect_rc3 = NetworkSetup(&arraySSID, &arrayPW);
                  if (connect_rc3 ==  RETCODE_OK)
                  {
  
                      printf("success \n");
  
                  }
  
                  else
                  {
                      Retcode_RaiseError(connect_rc3);
  
                  }
  
  
                  //Checking if content has been sent correctly 
                  printf("%s :arraySSID \n",arraySSID);
                  printf("%s :arrayPW \n",arrayPW);
                  printf("%s :arrayIP \n",arrayIP);
                  printf("%s: SSID \n", SSID_new);
                  printf("%s: IP \n", IP_new);
                  printf("%s: PW \n", PW_new);
                  //Deallocate space
  
                  free(arraySSID);
                  free(arrayPW);
                  free(arrayIP);
              }
  
              //Print received message
              printf("%s \n", message_received);
  
              incoming_message_count++;
          }
  

如果我在上面的函数中使用以下代码而不是 arraySSID 和 arrayPwd，即使 arraySSID 我也能够连接到新网络当我在控制台上打印时， > 和 arrayPwd 显示与 testSSID 和 testPW 相同的内容。

 char testSSID[] = "TestSSID";
 char testPW[] = "TestPwsd";
 Retcode_T connect_rc3 = NetworkSetup(&testSSID, &testPW);

如果我比较arraySSID、arrayPwd以及testSSID和testPwd的size >，为它们分配不同的大小。 arraySSID、arrayPwd 的大小始终为 4。

为此，我使用了以下代码:

 printf("%i \n", sizeof(arraySSID));
 printf("%i \n", sizeof(testSSID));

 printf("%d \n", sizeof(arrayPW));
 printf("%d \n", sizeof(testPW));

Answer 1

我想指出几个问题。

• C 中的 sizeof() 是一个有点神奇的函数。它不打印动态分配的内存的大小。相反，您最好从代码中打印 CountNumberItemsSSID。
• 另一件事是，在 C 中，您需要字符串以 null 结尾。因此，当您以这种方式计算字节时，如果您希望输出是有效的字符串，请始终允许 1 个额外字符并确保其为“\0”。
• 您的填充逻辑，我确信您通过覆盖所有字符串分配的内存来破坏内存。通过为 arraySSID 分配 CountNumberItemsSSID 字节，您只能从 0 到 (CountNumberItemsSSID-1) 写入，而不是像在 while() 循环中那样写入 arraySSID[CountNumberItemsSSID]。它们绝对应该是 (SSID < CountNumberItemsSSID)。

如果您解决了许多问题中的一些问题，我相信它应该可以正常工作。