Static variable - __cxa_guard_acquire and __cxa_guard_release implementation

Getting the following errors with the minimal test program below. Can work around by making variable global, but it would be good to fix the problem with static.

C:\Users\Ray\AppData\Local\Temp\build2036106428985831191.tmp\sketch_jul01b.cpp.o: In function `setup':
sketch_jul01b.cpp:(.text+0xc): undefined reference to `__cxa_guard_acquire'
sketch_jul01b.cpp:(.text+0x10): undefined reference to `__cxa_guard_release'
C:\Users\Ray\AppData\Local\Temp\build2036106428985831191.tmp\sketch_jul01b.cpp.o: In function `loop':
sketch_jul01b.cpp:(.text+0x25): undefined reference to `__cxa_guard_acquire'
sketch_jul01b.cpp:(.text+0x37): undefined reference to `__cxa_guard_release'
collect2.exe: error: ld returned 1 exit status
Error compiling.

void setup() 
{
}

void loop() 
{
    static uint32_t lastMillis = millis();
}

[reaper7]

declaring static variable in the loop? again and again and ....

I think the proper method is:

static uint32_t lastMillis;

void setup() 
{
}

void loop() 
{
    lastMillis = millis();
}

Static means it is initialised the first time loop() is executed and it retains its value when loop() is called again. The advantage is that the variable has local scope in loop() rather than being global.

Code above compiles OK for Arduino Uno etc but not for ESP8266. Maybe it's not supported on ESP8266, in which case note should be added to documentation page.

See www.learncpp.com/cpp-tutorial/43-static-duration-variables/

On 1 Jul 2015, at 20:00, reaper7 notifications@github.com wrote:

declaring a static variable in the loop? again and again and ....

I think the proper method is:

static uint32_t lastMillis;

void setup()
{
}

void loop()
{
lastMillis = millis();
}
—
Reply to this email directly or view it on GitHub.

[reaper7]

probably You are right :)

[Links2004]

@hackscribble what version and OS you use?
I use windows with the latest git and I can use static in the loop or in any other function it is working fine.

Arduino IDE 1.6.5 on Windows 8.

esp8266 version 1.6.4-673-g8cd3697 installed through Boards manager.

Board settings: Generic ESP8266 module, 80MHz, 512K, 115200.

EDIT Tried removing and reinstalling via Boards Manager, and also tested on 1.6.4. Same errors.

[Links2004]

ok can reproduce it, only using a function is not working.

no error with:

void setup() 
{
}

void loop() 
{
   static uint32_t lastMillis = 0;
   lastMillis = millis();
}

strange.

Note code will not have same functionality.

Thank you @Links2004 - that's a good workaround.

[Makuna]

Actually, the original code is flawed in that when the static is initialed you have no idea if millis has been initialized, so it should be avoided. You should use Links2004 code as the correct way to do this.

Thanks, @Makuna. I had not thought about that before, but I see exactly what you mean. As @Links2004 pointed out, his code is not exactly the same functionality. So I think I will change to a global variable, set to millis() at the end of setup().

[igrr]

Actually the original code is fine — C++ standard guarantees that local static initializer will be called exactly once, first time the function is executed. We just need to add __cxa_guard* implementations.

[Makuna]

@igrr when does the timer/variables get initialized for millis? Can you guarantee this happens before this static variable is initialised? This is my point.

[igrr]

In this case local static variable will be initialized the first time loop() function runs, that's what C++ standard guarantees. millis is certainly initialized before that, so that you can use it in setup()/loop().