warning C4706: assignment within conditional expression

[Mighty-Professional]

There is a few lines like:

if (keep and (not callback or (keep = callback(depth++, parse_event_t::object_start, result))))

That are causing warnings and make projects that treat warnings as errors unable to compile without fixing it or disabling warnings in the code.

Microsoft Visual Studio Compiler 2015

[nlohmann]

I understand the warnings, but they seem to be uncritical and rather pedantic. A solution would be to either restructure the code by moving the assignment out of the conditional and make it less readable or to add #pragmas and make the code even less readable. Any other suggestions?

[nlohmann]

Just to better understand MSVC at warning level 4: Would

if (keep and (not callback or ((keep = callback(depth++, parse_event_t::object_start, result))) != 0))

fix this issue?

[Mighty-Professional]

Yes that fixes the issue.

It could be rewritten I do not think it makes it any less clear, (I personally find that line with increment depth in the if a bit confusing to begin with. (But I am not a super experienced coder). )

For a easy fix you could just add:

#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable:4706) // assignment within conditional expression
#endif
...

#ifdef _MSC_VER
#pragma warning(pop)
#endif

There is already some code that ignores specific warnings for clang.

But its really up to you, as you said its not a critical problem. Just requires a tiny bit more work for someone integrating it.

Awesome library btw, easy to use and great features.

[nlohmann]

Ok. I think adding some != 0 is a bit nicer than adding another pragma in an ifdef. I wonder why MSVC is not silenced by another pair of parentheses like Clang.

Thanks for reporting! For a MSVC beginner - can you tell me how to compile a CMake project with this level of warnings?

Added: https://msdn.microsoft.com/en-us/library/7hw7c1he%28v=vs.80%29.aspx

[Mighty-Professional]

Sorry to say I do not use CMake nor know how. I just included the source file in my visual studio project.

That being said Warning level 4 is /W4 or even better EnableAllWarnings is /Wall.

[nlohmann]

Thanks! I shall add this to the AppVeyor build to see what else MSVC is warning about.

[nlohmann]

I ran an AppVeyor build with /Wall flags. All output is in the log.txt file.

There are two error types: C4706 (assignment within conditional expression) and C4710 (function not inlined). We can ignore C4710. The remaining warnings are:

[00:02:49]   c:\projects\json\src\json.hpp(8895): warning C4706: assignment within conditional expression [C:\projects\json\test\json_unit.vcxproj]
[00:02:49] n\src\json.hpp(8973): warning C4706: assignment within conditional expression [C:\projects\json\test\json_unit.vcxproj]
[00:02:49]   c:\projects\json\src\json.hpp(8895): warning C4706: assignment within conditional expression [C:\projects\json\test\json_unit.vcxproj]
[00:02:49]   c:\projects\json\src\json.hpp(8973): warning C4706: assignment within conditional expression [C:\projects\json\test\json_unit.vcxproj]

The two cases can be fixed with additional parenthesis and != 0.

[nlohmann]

@marsh0 Could you please check if the warnings disappeared?

[Mighty-Professional]

Yup, looks good now! Thanks!

[nlohmann]

Thanks for checking!

[eliasdaler]

Don't want to create a new thread, but I still have this warning on -W4 in VS 2017. Probably new expressions which should use the same pattern?

Or maybe #pragma will really be needed.

[nlohmann]

@eliasdaler Could you open an issue and paste the warnings? Please use the develop version.