Please enjoy a war story and have a laugh on me. The error in the code below kept me busier for longer than I will ever say. I have solved the problem. Many of you will solve it just by reading it, others will find the compiler warning useful. TBC I have the compiler warnings cranked up to the ma…

Thanks for posting that! Even given the warning, I don't understand the result either.

Reading an uninitialised value invokes undefined behaviour, so I guess that initialising flag (to false) solved the issue? [image] jremington: Even given the warning, I don't understand the result either. That is the fun part of UB, anything can happen. This is a nice example for our next d…

undefined value = undefined behavior

I believe an unitialized global variable flag would behave differently.

[image] 6v6gt: unitialized global variable flag It is my understanding the global variables are always initialized to some default, if not explicitly written into the code. But yes, in a test on the Arduino Uno using IDE 1.8.19, an "uninitialized" global flag does not exhibit the problem.

flag was not given an initial value. Would of worked ok as long as xx started off > 100 and we wouldn't know of this problem.

[image] alto777: TBC I have the compiler warnings cranked up to the max. Did you also include -pedantic? It can be a real life saver. [image] alto777: I think everything in the sketch is necessary to invoke this behaviour. The following sketch exhibits the same behaviour in your simul…

I remember some time ago now getting involved with a similar user problem. He was loading a struct, which contained a bool, from an EEPROM. With a new EEPROM, which was "0xFF" filled, he was having extreme difficulties with the behaviour of this bool variable. The conclusion we came to is that if y…

It would be very interesting to see the assembly code generated by the program in the OP, to understand exactly what it is doing. I'm really curious how the value of flag manages to print a different value in the two print statements.

[image] RayLivingston: It would be very interesting to see the assembly code generated by the program in the OP I extracted this from Wokwi as an experiment but have not studied it: sketch.ino.elf: file format elf32-avr Disassembly of section .text: 00000000 <__vectors>: 0: 0c 94 …

Odd code behaviour, just FYA

Projects Programming

anon56112670 August 1, 2023, 3:19pm 2

No initial value given.

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Odd code behaviour, just FYA

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