error: operator '!' has no right operand (ONLY_C_LOCALE)

[nschloe]

I get some weird errors when trying to compile with date.h:

/usr/include/date/date.h:3783:19: error: operator '!' has no right operand
 3783 | #if !ONLY_C_LOCALE
[...]

(For full details: https://launchpadlibrarian.net/488835127/buildlog_ubuntu-focal-amd64.waybar_0.9.2-202007161902-0fe0a856-1focal1_BUILDING.txt.gz.)

Seems like the ONLY_C_LOCALE is not defined, but I see

  #ifndef ONLY_C_LOCALE
  #  define ONLY_C_LOCALE 0
  #endif

towards the top of date.h.

Any idea what might be wrong?

[HowardHinnant]

This is a bug in the build system. Search for "-DONLY_C_LOCALE= in the build log you have. This is setting ONLY_C_LOCALE to "". The header date.h expects it to be set to 0 or 1, and if not defined, defaults it to 0.

[nschloe]

You're right, thanks for looking into it!

[nschloe]

Will need to reopen this. Can it be that the faulty definition comes from

target_compile_definitions( date INTERFACE
    #To workaround libstdc++ issue https://github.com/HowardHinnant/date/issues/388
    ONLY_C_LOCALE=$<IF:$<BOOL:${COMPILE_WITH_C_LOCALE}>,1,0>
    $<$<BOOL:${DISABLE_STRING_VIEW}>:HAS_STRING_VIEW=0> )

in date's CMakeLists.txt?

[HowardHinnant]

Could be. I don't really know CMake and personally avoid it whenever I can. If you've got a fix for this, I'd be happy to take it. For my use cases CMake causes far more problems than it solves.

If you just need date.h, then there is no installation other than just including it.

For tz.h, here are the build instructions I recommend and use: https://howardhinnant.github.io/date/tz.html#Installation

[nschloe]

I need to create a Debian build for date which includes tz.h. Doing as if there were only .c and .h will create the need for a lot of extra code that I'd rather avoid (because I don't know Debian's build system well enough).

[nschloe]

Okay, in the output dateTargets.cmake, one finds

INTERFACE_COMPILE_DEFINITIONS "ONLY_C_LOCALE=\$<IF:\$<BOOL:OFF>,1,0>;\$<\$<BOOL:OFF>:HAS_STRING_VIEW=0>"

which looks really fishy. This should probably be

INTERFACE_COMPILE_DEFINITIONS "ONLY_C_LOCALE=0"