Error with _min and _max macro

[warnerthuis]

Basic Infos

• This issue complies with the issue POLICY doc.
• I have read the documentation at readthedocs and the issue is not addressed there.
• I have tested that the issue is present in current master branch (aka latest git).
• I have searched the issue tracker for a similar issue.
• If there is a stack dump, I have decoded it.
• I have filled out all fields below.

Platform

• Hardware: [ESP-12]
• Core Version: [2.6.3]
• Development Env: [Arduino IDE]
• Operating System: [Windows]

Settings in IDE

• Module: [Generic ESP8266 Module]
• Flash Mode: [qio|dio|other]
• Flash Size: [4MB/1MB]
• lwip Variant: [v1.4|v2 Lower Memory|Higher Bandwidth]
• Reset Method: [ck|nodemcu]
• Flash Frequency: [40Mhz]
• CPU Frequency: [80Mhz|160MHz]
• Upload Using: [OTA|SERIAL]
• Upload Speed: [115200|other] (serial upload only)

Error with _min and _max macro

I have code which uses the _max and the _min macro. They are in the Arduino.h library.
That compiles ok with version 2.4.0 of the library where the definition of the maro's is:

#define _min(a,b) ((a)<(b)?(a):(b))
#define _max(a,b) ((a)>(b)?(a):(b))

Now in version 2.6.3 the definition is:

#define _min(a,b) ({ decltype(a) _a = (a); decltype(b) _b = (b); _a < _b? _a : _b; })
#define _max(a,b) ({ decltype(a) _a = (a); decltype(b) _b = (b); _a > _b? _a : _b; })

And the errors are:

C:\Users\warner\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.6.3\cores\esp8266/Arduino.h:254:85: internal compiler error: in cp_parser_abort_tentative_parse, at cp/parser.c:23793
 #define _min(a,b) ({ decltype(a) _a = (a); decltype(b) _b = (b); _a < _b? _a : _b; })
    pointer under ; after _b = (b)   ^

C:\Users\warner\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266\2.6.3\cores\esp8266/Arduino.h:255:53: note: in definition of macro '_max'
 #define _max(a,b) ({ decltype(a) _a = (a); decltype(b) _b = (b); _a > _b? _a : _b; })
   pointer under ; after _a = (a)           ^

MCVE Sketch

#include <Arduino.h>

void setup() {
  float op = 50;
  float ophi = 100;
  float oplo = 0;
  op = _max(oplo, _min(ophi, op));

}

void loop() {

}

Debug Messages

Debug messages go here

[d-a-v]

The new code in 2.6.3 is better than before (macro arguments can be reevaluated and this is bad).
You can replace these macro by std::min and std::max but they may not be usable in other arduino archs.
An internal compiler error is hard to reproduce.

Until we have gcc9.3, I suggest you add this in your code :

#ifdef ESP8266
#undef _min
#undef _max
//#define _min(a,b) ((a)<(b)?(a):(b))
//#define _max(a,b) ((a)>(b)?(a):(b))
#define _min(a,b) std::min(a,b)
#define _max(a,b) std::max(a,b)
#endif 

Alternatively you can try alpha version 0.0.2 of this core that already has gcc9.3.

[warnerthuis]

thanks, I'll try

[devyte]

For user code, it is strongly advised to use std::max/std::min, and not the macros.
The original macros you mention have a bug, where if you pass in anything that could have a side effect, you'll have the side effect evaluated twice.
The new macro improves on that by making a temporary local, which should then get optimized away, but such preprocessor macros are far from ideal. especially when it comes to casting.
In contrast, the standard std::min/std::max force same-type calculation without multiple side effects, and if you want to cast, you have to do so on purpose (which makes you think about what you're doing).

[devyte]

@warnerthuis did you try the std min/max?

[warnerthuis]

sorry for not mentioning that I used successfully the std min/max aproach. I was too busy with other projects (node-red). It works now in the new version.

[arbourp]

Wanted to leave a comment to follow-up here.
I ran into a very similar error while using the DMXInputNeoPixel demo from the LXESP8266UARTDMX library.

Oddly enough there is a comment saying that 'min' may fail so they used _min instead. pionting to this issue #263

At this point in time with 3.0.2 version of the esp8266 code I get
/STORAGE/home/megatron/.arduino15/packages/esp8266/hardware/esp8266/3.0.2/cores/esp8266/Arduino.h:243:19: error: statement-expressions are not allowed outside functions nor in template-argument lists

So I modified the code in the DMXInputNeoPixel demo to use 'min' instead of '_min' and it compiles fine.