c - 尝试在多个文件中使用 Azure-iot-sdk-c 序列化器模型时出现链接器错误

Question

我尝试在多个文件中使用带有 azure-iot-sdk-c 的序列化器模型。只要我只在主文件中使用它，一切都会编译。

但是当我在另一个头文件中声明模型，并在相应的 c 文件和主文件中使用它时，我收到链接器错误:

CMakeFiles/simplesample_amqp.dir/otherfile.c.o: In function `FromAGENT_DATA_TYPE_ContosoAnemometer':
otherfile.c:(.text+0x1165): multiple definition of `FromAGENT_DATA_TYPE_ContosoAnemometer'
CMakeFiles/simplesample_amqp.dir/simplesample_amqp.c.o:simplesample_amqp.c:(.text+0x1165): first defined here
collect2: error: ld returned 1 exit status
serializer/samples/simplesample_amqp/CMakeFiles/simplesample_amqp.dir/build.make:160: recipe for target 'serializer/samples/simplesample_amqp/simplesample_amqp' failed
make[2]: *** [serializer/samples/simplesample_amqp/simplesample_amqp] Error 1
CMakeFiles/Makefile2:3947: recipe for target 'serializer/samples/simplesample_amqp/CMakeFiles/simplesample_amqp.dir/all' failed
make[1]: *** [serializer/samples/simplesample_amqp/CMakeFiles/simplesample_amqp.dir/all] Error 2

我通过调整序列化器/samples/simplesample_amqp示例来尝试此操作:

diff --git a/serializer/samples/simplesample_amqp/CMakeLists.txt b/serializer/samples/simplesample_amqp/CMakeLists.txt
index 4f26060..52d55d7 100644
--- a/serializer/samples/simplesample_amqp/CMakeLists.txt
+++ b/serializer/samples/simplesample_amqp/CMakeLists.txt
@@ -11,6 +11,7 @@ endif()

 set(simplesample_amqp_c_files
 simplesample_amqp.c
+otherfile.c
 )

 if(WIN32)
@@ -21,6 +22,7 @@ endif()

 set(simplesample_amqp_h_files
 simplesample_amqp.h
+otherfile.h
 )

 IF(WIN32)
diff --git a/serializer/samples/simplesample_amqp/simplesample_amqp.c b/serializer/samples/simplesample_amqp/simplesample_amqp.c
index 0a9c9a8..b312c9c 100644
--- a/serializer/samples/simplesample_amqp/simplesample_amqp.c
+++ b/serializer/samples/simplesample_amqp/simplesample_amqp.c
@@ -26,24 +26,11 @@
 #include "certs.h"
 #endif // SET_TRUSTED_CERT_IN_SAMPLES

+#include "otherfile.h"
+
 /*String containing Hostname, Device Id & Device Key in the format:             */
 /*  "HostName=<host_name>;DeviceId=<device_id>;SharedAccessKey=<device_key>"    */
-static const char* connectionString = "[device connection string]";
-
-// Define the Model
-BEGIN_NAMESPACE(WeatherStation);
-
-DECLARE_MODEL(ContosoAnemometer,
-WITH_DATA(ascii_char_ptr, DeviceId),
-WITH_DATA(int, WindSpeed),
-WITH_DATA(float, Temperature),
-WITH_DATA(float, Humidity),
-WITH_ACTION(TurnFanOn),
-WITH_ACTION(TurnFanOff),
-WITH_ACTION(SetAirResistance, int, Position)
-);
-
-END_NAMESPACE(WeatherStation);
+static const char* connectionString = "";

 static char propText[1024];

@@ -199,10 +186,8 @@ void simplesample_amqp_run(void)
                     }
                     else
                     {
-                        myWeather->DeviceId = "myFirstDevice";
-                        myWeather->WindSpeed = avgWindSpeed + (rand() % 4 + 2);
-                        myWeather->Temperature = minTemperature + (rand() % 10);
-                        myWeather->Humidity = minHumidity + (rand() % 20);
+                                               myWeather->DeviceId = "myFirstDevice";
+                                               process_model(myWeather);

                         if (SERIALIZE(&destination, &destinationSize, myWeather->DeviceId, myWeather->WindSpeed, myWeather->Temperature, myWeather->Humidity) != CODEFIRST_OK)
                         {

其他文件.h:

// Define the Model
#include "serializer.h"
BEGIN_NAMESPACE(WeatherStation);

DECLARE_MODEL(ContosoAnemometer,
WITH_DATA(ascii_char_ptr, DeviceId),
WITH_DATA(int, WindSpeed),
WITH_DATA(float, Temperature),
WITH_DATA(float, Humidity),
WITH_ACTION(TurnFanOn),
WITH_ACTION(TurnFanOff),
WITH_ACTION(SetAirResistance, int, Position)
);

END_NAMESPACE(WeatherStation);

void process_model(ContosoAnemometer *myWeather);

其他文件.c:

#include "otherfile.h"

void process_model(ContosoAnemometer *myWeather) {
    int avgWindSpeed = 10;
    float minTemperature = 20.0;
    float minHumidity = 60.0;

    myWeather->WindSpeed = avgWindSpeed + (rand() % 4 + 2);
    myWeather->Temperature = minTemperature + (rand() % 10);
    myWeather->Humidity = minHumidity + (rand() % 20);
}

有什么方法可以在多个文件中使用序列化器模型吗？

请随时向我询问更多信息。现在我不太确定哪些信息与这篇文章相关。我前段时间严格尝试过 mqtt 序列化器示例，但据我所知，遇到了相同的错误。如果您无法模块化代码并且只有一个包含几乎所有内容的整体文件，那真的很困惑。

海湾合作委员会:gcc(Ubuntu 5.4.0-6ubuntu1~16.04.4)5.4.0 20160609

操作系统:4.4.0-97-generic#120-Ubuntu SMP 9 月 19 日星期二 17:28:18 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

Answer 1

您无法重用模型，但可以重用数据结构。这可以帮助您重用高达 80% 的定义。您可以将 JSON 结构设计为一组 DECLARE_STRUCT，如下所示在单独的文件中:

DECLARE_STRUCT(MyCommon,
   EDM_DATE_TIME_OFFSET, datetime,
   ascii_char_ptr, deviceid, 
   ascii_char_ptr, vin,
   int32_t, message_id, 
   int32_t, request_messageid 
);

之后，您可以使用 #include 为 С 文件中的不同模型重用 DECLARE_STRUCT:

BEGIN_NAMESPACE(cctcp);
 #include "MyCommon_json.inc"
DECLARE_MODEL(Message,
  WITH_DATA(EDM_GUID, edge_message_id),  
  WITH_DATA(int8_t, message_type),   
   WITH_DATA(MyCommon, tcu_common)
);