[Improvement] Add option to remove exceptions

[Mighty-Professional]

It would be nice to have the option to compile without exceptions for use on platforms where exceptions cannot be enabled., such as consoles etc.

Mainly for the reasons listed here: http://programmers.stackexchange.com/questions/113479/are-there-any-real-world-cases-for-c-without-exceptions

[nlohmann]

Instead of an exception, should the library just call exit() or abort?

[Mighty-Professional]

Just let it crash, crash hard crash early. You could throw in asserts for more protection. This will force the user to start using the library correctly. I do not see the average person disabling exceptions so its more of a special case.

[nlohmann]

This should be done together with #244, because then we have to touch all exceptions anyway.

[nlohmann]

Is there a more elegant way than to use preprocessor macros for this? (see https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_exceptions.html)

[Mighty-Professional]

The way that link details seems reasonable to me. At least the macro should only need to be used once with the try catch. Using -fno-exception may work with the standard library, but it will still fail to compile on any try catches or throws in your own code.

I have never done anything like that personally, I think most libraries either support them or dont. I have seen projects where you can define a preprocessor to remove exceptions though. This may cause to much extra code to be worth it.

Here is another library with the same discussion: gabime/spdlog#136. You could see how they implemented it.

[abarth]

Thanks for working on this issue! I'm interested in this change to because I'd like to use your library in a project that builds with -fno-exceptions.

[abarth]

Consider #define JSON_THROW(exception) std::abort() rather than defining JSON_THROW to nothing when JSON_NOEXCEPTION is set to avoid trigging control may reach end of non-void function for folks who build with [-Werror,-Wreturn-type]

[nlohmann]

I implemented this change. Unfortunately, the test suite cannot be compiled with -fno-exceptions (see catchorg/Catch2/issues/703). All you can do right now is

CPPFLAGS="-DJSON_NOEXCEPTION" make
test/json_unit -e

(one test fails, because an exception from std::map still occurs, but is no caught)

[nlohmann]

I shall merge this issue tomorrow.

[nlohmann]

Merged 1ab26ab. The library now respects -fno-exceptions. Additionally, exceptions can be switched off by defining JSON_NOEXCEPTION .