Why does static member std::map reset ESP8266 when outside the .ino file?

Question

Here's an example of a class which crashes the ESP8266-03 causing it to reset:

Test.hpp file:

#include <map>

class Test {
public:
    int data() const;

    Test(int x);
    ~Test();
protected:
    int _data;

    static std::map<int, Test const *>thing;

    static void _Reserve(Test const * const t);
};

Test.cpp file:

std::map<int, Test const *> Test::thing;

int Test::data() const 
{
    return this->_data;
}

void Test::_Reserve(Test const * const t) {
    Test::thing[t->data()] = t; // Works fine if this line is removed.
}

Test::Test(int x): _data(x) 
{
    Test::_Reserve(this);
}

Test::~Test() {};

Project.ino:

#include "ESP8266WiFi.h"
#include "Test.hpp"

Test test(2);

void setup() {
    Serial.begin(115200);
}

void loop() {
    Serial.print("Timer: ");
    Serial.println(millis());
    delay(1000);
}

The following does NOT crash the ESP8266-03 and prints the time as it should:

#include "ESP8266WiFi.h"
#include <map>

class Test {
public:
    int data() const 
    {
        return this->_data;
    }

    Test(int x): _data(x) 
    {
        Test::_Reserve(this);
    }
    ~Test() {};
protected:
    int _data;

    static std::map<int, Test const *>thing;

    static bool _Reserve(Test const * const t) {
        Test::thing[t->data()] = t;
    }
};

std::map<int, Test const *> Test::thing;

Test test(2);

void setup() {
    Serial.begin(115200);
}

void loop() {
    Serial.print("Timer: ");
    Serial.println(millis());
    delay(1000);
}

When the first version is uploaded to the board, I get the following in the serial monitor:

 ets Jan  8 2013,rst cause:1, boot mode:(1,7)


 ets Jan  8 2013,rst cause:4, boot mode:(1,7)

wdt reset

When I reset it and boot it regularly, no upload mode, the following repeats every ~1 second:

 ets Jan  8 2013,rst cause:1, boot mode:(3,7)

load 0x4010f000, len 1384, room 16 
tail 8
chksum 0x2d
csum 0x2d
v09f0c112
~ld

@Matt I believe I haven't tried that, but will check later on today. It's a bit strange since removing that line with a comment works fine. I can even add the same line to another method in the class (such as a new setData method, in that example up there) and it works properly... If I make the variable public, I can access it properly as well from outside the class. It probably has something to do with the constructor. — MayBee
– MayBee, Commented Jan 10, 2017 at 10:40

Mikael Patel · Accepted Answer · 2017-01-10 14:37:54Z

0

Why does static member std::map reset ESP8266 when outside the .ino file?

What happens if the Test() constructor is run before the map constructor? This is the problem: you are assuming order of execution.

Use a Singleton pattern or init() member function to force the ordering that is required.

Cheers!

answered Jan 10, 2017 at 14:37

Mikael Patel

7,9892 gold badges16 silver badges21 bronze badges

Like you said, it was an initialization issue. Turns out the Test instance in the first example is considered static, making it run before std::map is initialized since it's static code is in another translation unit (another file), but I think this comment better explains the reason for the problem: stackoverflow.com/a/26996015/3342154

MayBee
– MayBee

2017-01-10 20:58:37 +00:00
Commented Jan 10, 2017 at 20:58

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