`__EXCEPTIONS` is still defined as 1 without -fexceptions

[HenryAWE]

Version of emscripten/emsdk:

emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 4.0.15 (09f52557f0d48b65b8c724853ed8f4e8bf80e669)
clang version 22.0.0git (https:/github.com/llvm/llvm-project 3388d40684742e950b3c5d1d2dafe5a40695cfc1)
Target: wasm32-unknown-emscripten
Thread model: posix

According to the document, emcc disable exceptions by default,
but compile the code without -fexceptions, it still outputs 1

#ifdef __EXCEPTIONS
    std::cout << __EXCEPTIONS;
#endif

Some library use the macro to detect exceptions support at compile-time

[sbc100]

I don't think its quite true the emscripten disabled exceptions by default.

By default exception catching is disabled but exception thrown in enabled. This means that throwing can just trap (since there are no catches). See https://emscripten.org/docs/tools_reference/settings_reference.html#disable-exception-throwing and https://emscripten.org/docs/tools_reference/settings_reference.html#disable-exception-catching.

I believe this is different -fno-exceptions, which is what you want for __EXCEPTIONS to not be defined I belive.

[HenryAWE]

I don't think its quite true the emscripten disabled exceptions by default.

By default exception catching is disabled but exception thrown in enabled. This means that throwing can just trap (since there are no catches). See https://emscripten.org/docs/tools_reference/settings_reference.html#disable-exception-throwing and https://emscripten.org/docs/tools_reference/settings_reference.html#disable-exception-catching.

I believe this is different -fno-exceptions, which is what you want for __EXCEPTIONS to not be defined I belive.

If this is a designed behavior, how can I detect it (no catching) by any macro at compile-time?

So I can have my library don't throw exceptions on Emscripten even without the -fno-exceptions flag.

[sbc100]

If this is a designed behavior, how can I detect it (no catching) by any macro at compile-time?

There is no macro for that builtin. You would need to do something like -DNO_EXCEPTION_CATCHING yourself.

[sbc100]

If this is a designed behavior, how can I detect it (no catching) by any macro at compile-time?

There is no macro for that builtin. You would need to do something like -DNO_EXCEPTION_CATCHING yourself.

@aheejin can you confirm?

[aheejin]

Yeah I am not aware of any macro that is controlled by our catching behavior.