unresolved external symbol "private: static struct MQTTAsync_createOptions const mqtt::create_options::DFLT_C_STRUCT"

[MikeMakes]

Compiling latest paho cpp with the latest paho c (installed without errors), with visual code 2019 for windows 10 results in:

LNK2019 unresolved external symbol "private: static struct MQTTAsync_createOptions const mqtt::create_options::DFLT_C_STRUCT" (?DFLT_C_STRUCT@create_options@mqtt@@0UMQTTAsync_createOptions@@b) referenced in function main async_publish_time C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\samples\async_publish_time.obj

at the compilation of Project: rpc_math_srvr, Configuration: Release x64

All was build as Readme says, it does not work either compiling from VS gui or powershell.

• OS: [Windows 10 x64
• Visual Code 2019
• Latest master paho mqtt c & cpp

Thanks you for this library, amazing work, I used it a lot recently ^^

VS compile output [edited, more readable]

1>------ Build started: Project: ZERO_CHECK, Configuration: Release x64 ------
1>Checking Build System
2>------ Build started: Project: paho-cpp-objs, Configuration: Release x64 ------
2>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/src/CMakeLists.txt
2>async_client.cpp
2>client.cpp
2>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\src\mqtt/client.h(71,8): warning C4834: discarding return value of function with 'nodiscard' attribute
2>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\src\mqtt/client.h(74,8): warning C4834: discarding return value of function with 'nodiscard' attribute
2>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\src\mqtt/client.h(81,8): warning C4834: discarding return value of function with 'nodiscard' attribute
2>connect_options.cpp
2>create_options.cpp
2>disconnect_options.cpp
2>iclient_persistence.cpp
2>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\src\iclient_persistence.cpp(113,14): warning C4267: '=': conversion from 'size_t' to 'int', possible loss of data
2>message.cpp
2>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\src\message.cpp(115,38): warning C4267: '=': conversion from 'size_t' to 'int', possible loss of data
2>properties.cpp
2>response_options.cpp
2>ssl_options.cpp
2>string_collection.cpp
2>subscribe_options.cpp
2>token.cpp
2>topic.cpp
2>will_options.cpp
2>Generating Code...
2>paho-cpp-objs.vcxproj -> C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\paho-cpp-objs.dir\Release\paho-cpp-objs.lib
2>Done building project "paho-cpp-objs.vcxproj".
3>------ Build started: Project: paho-mqttpp3, Configuration: Release x64 ------
4>------ Build started: Project: paho-mqttpp3-static, Configuration: Release x64 ------
3>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/src/CMakeLists.txt
3>Auto build dll exports
3> Creating library C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/build/src/Release/paho-mqttpp3.lib and object C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/build/src/Release/paho-mqttpp3.exp
4>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/src/CMakeLists.txt
3>paho-mqttpp3.vcxproj -> C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\Release\paho-mqttpp3.dll
5>------ Build started: Project: async_consume, Configuration: Release x64 ------
6>------ Build started: Project: async_publish, Configuration: Release x64 ------
7>------ Build started: Project: async_publish_time, Configuration: Release x64 ------
8>------ Build started: Project: async_subscribe, Configuration: Release x64 ------
9>------ Build started: Project: data_publish, Configuration: Release x64 ------
10>------ Build started: Project: mqttpp_chat, Configuration: Release x64 ------
11>------ Build started: Project: pub_speed_test, Configuration: Release x64 ------
4>paho-mqttpp3-static.vcxproj -> C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\Release\paho-mqttpp3-static.lib
5>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/src/samples/CMakeLists.txt
5>async_consume.cpp
10>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/src/samples/CMakeLists.txt
7>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/src/samples/CMakeLists.txt
12>------ Build started: Project: rpc_math_cli, Configuration: Release x64 ------
7>async_publish_time.cpp
10>mqttpp_chat.cpp
6>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/src/samples/CMakeLists.txt
12>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/src/samples/CMakeLists.txt
8>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/src/samples/CMakeLists.txt
12>rpc_math_cli.cpp
6>async_publish.cpp
9>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/src/samples/CMakeLists.txt
8>async_subscribe.cpp
11>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/src/samples/CMakeLists.txt
9>data_publish.cpp
11>pub_speed_test.cpp
9>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\src\samples\data_publish.cpp(108,44): warning C4996: 'localtime': This function or variable may be unsafe. Consider using localtime_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
5>async_consume.vcxproj -> C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\samples\Release\async_consume.exe
13>------ Build started: Project: rpc_math_srvr, Configuration: Release x64 ------
7>async_publish_time.obj : error LNK2019: unresolved external symbol "private: static struct MQTTAsync_createOptions const mqtt::create_options::DFLT_C_STRUCT" (?DFLT_C_STRUCT@create_options@mqtt@@0UMQTTAsync_createOptions@@b) referenced in function main
7>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\samples\Release\async_publish_time.exe : fatal error LNK1120: 1 unresolved externals
7>Done building project "async_publish_time.vcxproj" -- FAILED.
14>------ Build started: Project: sync_consume, Configuration: Release x64 ------
10>mqttpp_chat.vcxproj -> C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\samples\Release\mqttpp_chat.exe
13>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/src/samples/CMakeLists.txt
15>------ Build started: Project: sync_publish, Configuration: Release x64 ------
8>async_subscribe.vcxproj -> C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\samples\Release\async_subscribe.exe
13>rpc_math_srvr.cpp
14>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/src/samples/CMakeLists.txt
16>------ Build started: Project: topic_publish, Configuration: Release x64 ------
15>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/src/samples/CMakeLists.txt
6>async_publish.vcxproj -> C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\samples\Release\async_publish.exe
16>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/src/samples/CMakeLists.txt
14>sync_consume.cpp
15>sync_publish.cpp
12>rpc_math_cli.vcxproj -> C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\samples\Release\rpc_math_cli.exe
9>data_publish.vcxproj -> C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\samples\Release\data_publish.exe
16>topic_publish.cpp
9>Done building project "data_publish.vcxproj".
13>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\src\mqtt/client.h(71,8): warning C4834: discarding return value of function with 'nodiscard' attribute
13>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\src\mqtt/client.h(74,8): warning C4834: discarding return value of function with 'nodiscard' attribute
13>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\src\mqtt/client.h(81,8): warning C4834: discarding return value of function with 'nodiscard' attribute
11>pub_speed_test.vcxproj -> C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\samples\Release\pub_speed_test.exe
14>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\src\mqtt/client.h(71,8): warning C4834: discarding return value of function with 'nodiscard' attribute
14>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\src\mqtt/client.h(74,8): warning C4834: discarding return value of function with 'nodiscard' attribute
14>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\src\mqtt/client.h(81,8): warning C4834: discarding return value of function with 'nodiscard' attribute
15>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\src\mqtt/client.h(71,8): warning C4834: discarding return value of function with 'nodiscard' attribute
15>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\src\mqtt/client.h(74,8): warning C4834: discarding return value of function with 'nodiscard' attribute
15>C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\src\mqtt/client.h(81,8): warning C4834: discarding return value of function with 'nodiscard' attribute
16>topic_publish.vcxproj -> C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\samples\Release\topic_publish.exe
14>sync_consume.vcxproj -> C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\samples\Release\sync_consume.exe
14>Done building project "sync_consume.vcxproj".
15>sync_publish.vcxproj -> C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\samples\Release\sync_publish.exe
15>Done building project "sync_publish.vcxproj".
13>rpc_math_srvr.vcxproj -> C:\Users\Usuario\Desktop\VDB\dependencias\paho.mqtt.cpp\build\src\samples\Release\rpc_math_srvr.exe
13>Done building project "rpc_math_srvr.vcxproj".
17>------ Build started: Project: ALL_BUILD, Configuration: Release x64 ------
17>Building Custom Rule C:/Users/Usuario/Desktop/VDB/dependencias/paho.mqtt.cpp/CMakeLists.txt
========== Build: 16 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

[fpagliughi]

OK. Thanks. I haven't tried this on Windows yet. I'll have a look and get it fixed.

[GiuServ]

I have the same problem, on windows too.

unresolved external symbol "private: static struct MQTTAsync_createOptions const mqtt::create_options::DFLT_C_STRUCT" (?DFLT_C_STRUCT@create_options@mqtt@@0UMQTTAsync_createOptions@@B)

[fpagliughi]

I just tried this and it worked for me. So I'm not seeing the problem.

The missing struct is (the only thing) defined in create_options.cpp:
https://github.com/eclipse/paho.mqtt.cpp/blob/076fc9977d07c25fa9fef1e19026d8be069c8e94/src/create_options.cpp#L24-L25

The source file is included in CMake:
https://github.com/eclipse/paho.mqtt.cpp/blob/076fc9977d07c25fa9fef1e19026d8be069c8e94/src/CMakeLists.txt#L48

And when I run CMake, the source file is listed in the src/paho-cpp-objs.vcxproj file that it produces:

...
    <ClCompile Include="K:\mqtt\paho-mqttpp\src\async_client.cpp" />
    <ClCompile Include="K:\mqtt\paho-mqttpp\src\client.cpp" />
    <ClCompile Include="K:\mqtt\paho-mqttpp\src\connect_options.cpp" />
    <ClCompile Include="K:\mqtt\paho-mqttpp\src\create_options.cpp" />          <--- ***
    <ClCompile Include="K:\mqtt\paho-mqttpp\src\disconnect_options.cpp" />
...

Sorry, I'm not much of a Windows programmer. Do you have any ideas? Are all these present on your local machines?

[fpagliughi]

Has this been resolved?

[GiuServ]

For my application i made a workaround, since everything compiles good but something wrong happends when using mqtt.cpp inside my application.
I edited the MQTTAsync_send function in MQTTAsync.c (https://github.com/eclipse/paho.mqtt.c/blob/master/src/MQTTAsync.c) changing this part:

if (m->createOptions == NULL) rc = MQTTASYNC_DISCONNECTED; else if (m->createOptions->sendWhileDisconnected == 0) rc = MQTTASYNC_DISCONNECTED; else if (m->shouldBeConnected == 0 && (m->createOptions->struct_version < 2 || m->createOptions->allowDisconnectedSendAtAnyTime == 0)) rc = MQTTASYNC_DISCONNECTED;

with this:

if (m->shouldBeConnected == 0 && m->createOptions != NULL && (m->createOptions->struct_version < 2 || m->createOptions->allowDisconnectedSendAtAnyTime == 0)) rc = MQTTASYNC_DISCONNECTED;

Obviously this solution is good just for me since i wanted to send messages while disconnected.

Have you changed/fixed something? Because i can try to update the sources and try to recompile.

[zhenhua10]

src\mqtt\create_options.h The DFLT_C_STRUCT problem of line 58 ， I am modifying the 40 line “MQTTAsync_createOptions DFLT_C_STRUCT = MQTTAsync_createOptions_initializer;” and deleting "create"_ options.cpp "24 line const MQTTAsync_createOptions create_options::DFLT_C_STRUCT = MQTTAsync_createOptions_initializer;

[MikeMakes]

Hi, sorry for not posting again, this issue was related to a client PC which I lost access. I think we workarounded it using another version of VScode.

Later I tried again in another system with VScode 2019 and it worked, the only difference I can think of was the system localization being the one who works USA english and the broken one SPAIN spanish I dont know how this could be related but I have faced problems in VScode with other libs bc of this.

[phuongtran7]

I just got the same problem when installing 1.2.0 from Vcpkg and using VS19 16.9.3. Building the library works just fine but whenever I use the mqtt::create_options_builder, the above error showed up. I've not tried building the library myself as I want Vcpkg to manage everything for me. Is there any work around for this?

[GiuServ]

I retried it today, with updated source of mqtt and mqtccpp.
I can build from sources, but when using mqtt::create_options_builder() the problem is still here.
I both tried with vs2017 and vs2019.

[GiuServ]

src\mqtt\create_options.h The DFLT_C_STRUCT problem of line 58 ， I am modifying the 40 line “MQTTAsync_createOptions DFLT_C_STRUCT = MQTTAsync_createOptions_initializer;” and deleting "create"_ options.cpp "24 line const MQTTAsync_createOptions create_options::DFLT_C_STRUCT = MQTTAsync_createOptions_initializer;

With this solution it works.

[ultrahabbit]

I have encountered the same problem with Visual Studio 2019 for 2 projects: unit_tests and async_public_time. Obviously, the 2 projects are less the input library paho-cpp-objs.lib. After adding the paho-cpp-objs.lib, 2 projects are built successfully.

Additional, unit_tests project required use C++20 language to build.

Hope the developer modify the configure file of CMake for the above information.

[artemiuzzz]

The issue is still reproduced, in my case helped moving ctor from src\mqtt\create_options.h to cpp file:

create_options::create_options() : opts_( DFLT_C_STRUCT )
{}

[fpagliughi]

^^^ OK. I will do what @artemiuzzz suggests and move the constructor out of the header file and into the .cpp file.

[fpagliughi]

I assume the update fixes it for everyone. It not, please feel free to reopen this issue.