#include or #error inside #if not working as expected

[NicoHood]

Ref: #18
Used official Leonardo board

New issue, just try this sketch:

#include <Arduino.h>
#if !defined(USBCON)
#error
#endif

void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}

I have the same error within libraries unless I include Arduino.h. Not sure if this is intended, not sure if Arduino.h Includes the register definitions but I think this should be passed by default since things like DDRB should always be accessible without arduino layer.

However its weird that you can inlcude Arduino.h and it works then. And eve more weird that this does NOT help in a simple sketch.

[matthijskooijman]

I have the same error within libraries unless I include Arduino.h. Not sure if this is intended, not sure if Arduino.h Includes the register definitions but I think this should be passed by default since things like DDRB should always be accessible without arduino layer.

Inside libraries, no preprocessing is done, so you will always need to include what you need. Including Arduino.h is easiest, since that will get you mostly everything. This has been the case as long as I remember.

However, inside the sketch it should just work. I just tried your sketch, and got the same error. Something weird is going on here. Look at the command used to compile the sketch:

"/home/matthijs/docs/Electronics/Arduino/Arduino-1.5/build/linux/work/hardware/tools/avr/bin/avr-g++" -c -g -Os -w -std=gnu++11 -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics  -w -x c++ -M -MG -MP -mmcu=atmega32u4 -DF_CPU=16000000L -DARDUINO=10606 -DARDUINO_AVR_LEONARDO -DARDUINO_ARCH_AVR  -DUSB_VID=0x2341 -DUSB_PID=0x8036 '-DUSB_MANUFACTURER="Unknown"' '-DUSB_PRODUCT="Arduino Leonardo"'  "/tmp/buildb2ade5cdfb0cba832a5548a0d4d12d00.tmp/sketch/sketch_oct13a.ino.cpp"

Note that this does not include any -I options, so I don't think Arduino.h will be found. This might not trigger an error, but just a warning, which seem to be disabled by the -w option (which is weird, since the preferences have warnings enabled - I'll report a separate bug about this).

If I remove the #error, compilation works again. Looking at the commands, I see that g++ is called a few times on the sketch, each time adding some include paths. I suspect that this means that this is not actually compiling the sketch, but just doing preprocessing to collect missing includes, and this process doesn't currently support handling preprocessor errors. I suspect that these errors should just be ignored, if there are any missing includes before the error.

However, it also seems that these initial preprocessing attempts are done without Arduino.h added (looking at the preprocessed .cpp file), which means that if libraries are being selected based on stuff from Arduino.h, the preprocessing will not properly match the final compilation.

[NicoHood]

I also had the "error" sometimes, that a warning appeared and after another warning was solves the other warning disappeared. Even though it was clearly not there. Might be so minor that it ignores it then?

[ffissore]

Indeed that first gcc call is gcc -M which is used to gather includes. However, gcc does execute directives, thus the error triggered by #error. Unless you have suggestions, I would close this as wontfix, as I don't know a better way to do arduino magic

[matthijskooijman]

I guess that adding the #include <Arduino.h> line _before running the gcc -M command would help in this case. Additionally, adding library include paths one by one (as originally suggested by @PaulStoffregen) would help to prevent similar problems for defines from library header files (as well as preventing issues with "oscillations" in the library include list / issues with libraries being included when they should not be).

[NicoHood]

I need to include it in libraries as well which is a bug I think. I dont think that I need to include Arduino.h for register names. there must be something wrong here? The sketch above was just a simpler showcase, but the real (important) bug is inside libraries.

[matthijskooijman]

@NicoHood, I'm not sure I understand your last comment? You're saying you must add #include <Arduino.h> inside your library source files? That is totally expected and has been like that always. Or did I misunderstand?

[NicoHood]

Yes. Do I need to include Arduino.h just to get the USBCON definition? I remombered (might be wrong) To not need this, since its a normal reg and those register definitions should be passed via compiler?