Create an Arduino ESP8266 library - c++

Question

I would like to create a Arduino library for an ESP8266or ESP32 microcontroller. I wrote a test library which running on an Arduino Nano board with no problem. Here the library cpp file:
#include "Test.h"
Test::Test(){
}
uint32_t Test::libTest(strcttest* t){
uint32_t w;
w = t->a;
return w;
}
Here's the the header file :
#include <Arduino.h>
typedef struct {
uint32_t a;
uint32_t b;
}strcttest;
class Test
{
public:
Test();
uint32_t libTest(strcttest* t);
private:
};
And last but not least the Arduino ino file:
#include <Test.h>
//Instante Test
Test t;
void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
Serial.println("Start");
}
void loop() {
// put your main code here, to run repeatedly:
//Create structure
strcttest *tt;
tt->a=1;
tt->b=2;
//Output result
Serial.println (t.libTest(tt));
delay(1000);
}
Every compile fine with an Arduino Nano board as well as with ESP8266/ESP32 boards. When I run it on the Nano Board i get the expected result:
Start
1
1
1
1
1
1
1
1
1
...
When I run it on the ESP8266 board I get the following crash result:
l*⸮⸮⸮⸮CI>⸮⸮⸮HB⸮⸮Start
Exception (28):
epc1=0x402024f8 epc2=0x00000000 epc3=0x00000000 excvaddr=0x00000000 depc=0x00000000
ctx: cont
sp: 3ffef7d0 end: 3ffef9a0 offset: 01a0
>>>stack>>>
3ffef970: feefeffe 00000000 3ffee950 40201eb4
3ffef980: feefeffe feefeffe 3ffee96c 40202340
3ffef990: feefeffe feefeffe 3ffee980 40100108
<<<stack<<<
7!a!*6⸮⸮⸮Start
Exception (28):
epc1=0x402024f8 epc2=0x00000000 epc3=0x00000000 excvaddr=0x00000000 depc=0x00000000
ctx: cont
sp: 3ffef7d0 end: 3ffef9a0 offset: 01a0
>>>stack>>>
3ffef970: feefeffe 00000000 3ffee950 40201eb4
3ffef980: feefeffe feefeffe 3ffee96c 40202340
3ffef990: feefeffe feefeffe 3ffee980 40100108
<<<stack<<<
ĜBs⸮`⸮"⸮⸮Start
...
And last but not least on the ESP Development board I receive:
i%M/⸮`⸮i%M7
⸮⸮%Q=qU=\Md⸮aGd<$⸮Start
Guru Meditation Error of type LoadProhibited occurred on core 1. Exception was unhandled.
Register dump:
PC : 0x400dde93 PS : 0x00060030 A0 : 0x800d0570 A1 : 0x3ffc7390
A2 : 0x3ffc1c30 A3 : 0x00000000 A4 : 0x0800001c A5 : 0xffffffff
A6 : 0xffffffff A7 : 0x00060d23 A8 : 0x800832e9 A9 : 0x3ffc7380
A10 : 0x00000003 A11 : 0x00060023 A12 : 0x00060020 A13 : 0x00000003
A14 : 0x00000001 A15 : 0x00000000 SAR : 0x0000001f EXCCAUSE: 0x0000001c
EXCVADDR: 0x00000000 LBEG : 0x400014fd LEND : 0x4000150d LCOUNT : 0xffffffff
Backtrace: 0x400dde93:0x3ffc7390 0x400d0570:0x3ffc73b0 0x400d79b0:0x3ffc73d0
CPU halted.
So my question is: What I am doing wrong. What do i miss. What I haven't understood with Arduino IDE, cpp, pointers, etc.
Sorry I forgot: I use Arduino IDE 1.8.2

Answer 1

strcttest *tt; is your problem. You're not allocating memory for and creating an object of type strcttest - you're merely allocating memory for a pointer to an object of that type. Basically, the code should crash everywhere when your code gets to the line tt->a=1; The fact that it doesn't when run on the Nano is basically dumb luck..
Think of the case where you have a char* variable and then try to copy a string to it - it will crash too, since you dont have any storage space for the string itself - you only have a few bytes allocated that store the address of the string.
The following is a more reasonable implementation of your void loop() function:
void loop() {
// put your main code here, to run repeatedly:
//Create structure
strcttest tt;
tt.a=1;
tt.b=2;
//Output result
Serial.println (t.libTest(&tt));
delay(1000);
}
Another (slower, due to use of new and delete) implementation may look like this:
void loop() {
// put your main code here, to run repeatedly:
//Create structure
strcttest *tt = new strcttest;
tt->a=1;
tt->b=2;
//Output result
Serial.println (t.libTest(tt));
delete tt;
delay(1000);
}

Answer 2

For ESP32 and ESP8266, have a excellent tool to help in crashes situations,
like that You report.
This integrates to Arduino IDE
See it in: https://github.com/me-no-dev/EspExceptionDecoder