error C3779: 'AIToolbox::IndexMapIterator<IdsIterator,Container>::operator *': a function that returns 'auto' cannot be used before it is defined

[jianchenghao]

When the .sln is built, there would be error C3779, e.g., 'AIToolbox::IndexMapIterator<IdsIterator,Container>::operator *': a function that returns 'auto' cannot be used before it is defined. Is there any method to solve it?

[Svalorzen]

This seems strange. Is there any more context to this error?

[jianchenghao]

Build started...
1>------ Build started: Project: ZERO_CHECK, Configuration: RelWithDebInfo x64 ------
1>Checking Build System
2>------ Build started: Project: AIToolboxMDP, Configuration: RelWithDebInfo x64 ------
3>------ Build started: Project: Global_ToolsTests, Configuration: RelWithDebInfo x64 ------
4>------ Build started: Project: Global_UtilsAdamTests, Configuration: RelWithDebInfo x64 ------
5>------ Build started: Project: Global_UtilsCoreTests, Configuration: RelWithDebInfo x64 ------
6>------ Build started: Project: Global_UtilsIOTests, Configuration: RelWithDebInfo x64 ------
7>------ Build started: Project: Global_UtilsProbabilityTests, Configuration: RelWithDebInfo x64 ------
8>------ Build started: Project: Global_UtilsPruneTests, Configuration: RelWithDebInfo x64 ------
2>Building Custom Rule D:/OneDrive - HKUST Connect/VS_Code/VStools/AI-Toolbox/src/CMakeLists.txt
3>Building Custom Rule D:/OneDrive - HKUST Connect/VS_Code/VStools/AI-Toolbox/test/CMakeLists.txt
4>Building Custom Rule D:/OneDrive - HKUST Connect/VS_Code/VStools/AI-Toolbox/test/CMakeLists.txt
6>Building Custom Rule D:/OneDrive - HKUST Connect/VS_Code/VStools/AI-Toolbox/test/CMakeLists.txt
5>Building Custom Rule D:/OneDrive - HKUST Connect/VS_Code/VStools/AI-Toolbox/test/CMakeLists.txt
7>Building Custom Rule D:/OneDrive - HKUST Connect/VS_Code/VStools/AI-Toolbox/test/CMakeLists.txt
2>Seeder.cpp
8>Building Custom Rule D:/OneDrive - HKUST Connect/VS_Code/VStools/AI-Toolbox/test/CMakeLists.txt
4>UtilsAdamTests.cpp
6>UtilsIOTests.cpp
7>UtilsProbabilityTests.cpp
8>UtilsPruneTests.cpp
3>ToolsTests.cpp
5>UtilsCoreTests.cpp
2>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/Half.h(1,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
2>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/BFloat16.h(1,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
2>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/GenericPacketMathFunctions.h(676,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
4>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/Half.h(1,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
8>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/Half.h(1,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
7>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/Half.h(1,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
4>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/BFloat16.h(1,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
4>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/GenericPacketMathFunctions.h(676,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
6>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/Half.h(1,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
6>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/BFloat16.h(1,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
7>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/BFloat16.h(1,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
7>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/GenericPacketMathFunctions.h(676,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
8>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/BFloat16.h(1,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
8>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/GenericPacketMathFunctions.h(676,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
6>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/GenericPacketMathFunctions.h(676,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
6>D:\OneDrive - HKUST Connect\VS_Code\VStools\AI-Toolbox\test\UtilsIOTests.cpp(33,67): warning C4267: 'argument': conversion from 'size_t' to '_Ty', possible loss of data
6> with
6> [
6> _Ty=unsigned int
6> ]
2>D:\OneDrive - HKUST Connect\VS_Code\VStools\AI-Toolbox\src\Seeder.cpp(10,78): warning C4244: '=': conversion from '_Rep' to 'unsigned int', possible loss of data
2> with
2> [
2> _Rep=std::chrono::system_clock::rep
2> ]
6>D:\OneDrive - HKUST Connect\VS_Code\VStools\AI-Toolbox\test\UtilsIOTests.cpp(66,67): warning C4267: 'argument': conversion from 'size_t' to '_Ty', possible loss of data
6> with
6> [
6> _Ty=unsigned int
6> ]
3>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/Half.h(1,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
8>D:\OneDrive - HKUST Connect\VS_Code\VStools\AI-Toolbox\include\AIToolbox/Utils/IndexMap.hpp(45,52): error C3779: 'AIToolbox::IndexMapIterator<IdsIterator,Container>::operator *': a function that returns 'auto' cannot be used before it is defined
8>D:\OneDrive - HKUST Connect\VS_Code\VStools\AI-Toolbox\include\AIToolbox/Utils/IndexMap.hpp(43): message : see declaration of 'AIToolbox::IndexMapIterator<IdsIterator,Container>::operator *'
8>D:\OneDrive - HKUST Connect\VS_Code\VStools\AI-Toolbox\include\AIToolbox/Utils/IndexMap.hpp(148): message : see reference to class template instantiation 'AIToolbox::IndexMapIterator<IdsIterator,Container>' being compiled
8>D:\OneDrive - HKUST Connect\VS_Code\VStools\AI-Toolbox\include\AIToolbox/Utils/IndexMap.hpp(46,58): error C3779: 'AIToolbox::IndexMapIterator<IdsIterator,Container>::operator *': a function that returns 'auto' cannot be used before it is defined
8>D:\OneDrive - HKUST Connect\VS_Code\VStools\AI-Toolbox\include\AIToolbox/Utils/IndexMap.hpp(43): message : see declaration of 'AIToolbox::IndexMapIterator<IdsIterator,Container>::operator *'
8>D:\OneDrive - HKUST Connect\VS_Code\VStools\AI-Toolbox\include\AIToolbox/Utils/IndexMap.hpp(317,52): error C3779: 'AIToolbox::IndexSkipMapIterator<IdsContainer,Container>::operator *': a function that returns 'auto' cannot be used before it is defined
3>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/BFloat16.h(1,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
3>D:\OneDrive - HKUST Connect\VS_Code\VStools\eigen-3.4.0\Eigen\src/Core/arch/Default/GenericPacketMathFunctions.h(676,1): warning C4819: The file contains a character that cannot be represented in the current code page (936). Save the file in Unicode format to prevent data loss
7>D:\OneDrive - HKUST Connect\VS_Code\VStools\AI-Toolbox\include\AIToolbox/Utils/Probability.hpp(455,31): warning C4244: 'initializing': conversion from 'const double' to 'int', possible loss of data
7>D:\OneDrive - HKUST Connect\VS_Code\VStools\AI-Toolbox\test\UtilsProbabilityTests.cpp(57): message : see reference to function template instantiation 'size_t AIToolbox::VoseAliasSampler::sampleProbabilityAIToolbox::RandomEngine(G &) const' being compiled

[Svalorzen]

What compiler version are you using?

[jianchenghao]

It is Visual Studio 2019 (v142).

[Svalorzen]

Which version of 2019? I'm trying to reproduce the error but I haven't been able to yet.
There's a high likelihood that the problem is from VS, and updating it to the latest version might resolve your issues.

[Svalorzen]

Ah, I think I was just able to. VS19.29 16.11 enabled C++20, and gives your error with the code: https://godbolt.org/z/o8x6d56sT

However, this disappears with the latest version of Visual Studio 19: https://godbolt.org/z/8KsE97dGP

Updating Visual Studio as much as possible is probably the only real way to fix this problem. VS was always a bit slow in fully supporting template features, so it's always good to keep it as up to date as possible.

[jianchenghao]

Thank you for your help. The version I used is Microsoft Visual Studio Community 2019 Version 16.11.17

[jianchenghao]

With the latest version of VS, there are still some errors. The first error occurs as below:
5>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Microsoft\VC\v170\Microsoft.CppCommon.targets(157,5): error MSB3073: The command "setlocal
5>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Microsoft\VC\v170\Microsoft.CppCommon.targets(157,5): error MSB3073: rsync -r "D:/OneDrive - HKUST Connect/VS_Code/VStools/AI-Toolbox/test/data" "D:/OneDrive - HKUST Connect/VS_Code/VStools/AI-Toolbox/build/test"
5>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Microsoft\VC\v170\Microsoft.CppCommon.targets(157,5): error MSB3073: if %errorlevel% neq 0 goto :cmEnd
5>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Microsoft\VC\v170\Microsoft.CppCommon.targets(157,5): error MSB3073: :cmEnd
5>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Microsoft\VC\v170\Microsoft.CppCommon.targets(157,5): error MSB3073: endlocal & call :cmErrorLevel %errorlevel% & goto :cmDone
5>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Microsoft\VC\v170\Microsoft.CppCommon.targets(157,5): error MSB3073: :cmErrorLevel
5>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Microsoft\VC\v170\Microsoft.CppCommon.targets(157,5): error MSB3073: exit /b %1
5>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Microsoft\VC\v170\Microsoft.CppCommon.targets(157,5): error MSB3073: :cmDone
5>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Microsoft\VC\v170\Microsoft.CppCommon.targets(157,5): error MSB3073: if %errorlevel% neq 0 goto :VCEnd
5>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Microsoft\VC\v170\Microsoft.CppCommon.targets(157,5): error MSB3073: :VCEnd" exited with code 9009.
5>Done building project "Global_UtilsCoreTests.vcxproj" -- FAILED.

[Svalorzen]

Looks like this error? https://stackoverflow.com/questions/10504377/added-and-removed-file-in-visualstudio-compile-errors

[jianchenghao]

I run the code again in administrator privilege, however, the error is still there. Is it because I used the Windows system?

[Svalorzen]

To be honest I don't have much experience on Windows, so I can't really help you. Googling is more likely to help in finding a solution.

If you find out that the solution turns out to be something I have to change in the project, I'll gladly do so. Until then I can't really do much, sorry.