I have this CommandHandler type that relies on the Serial object. I want to be able to declare the variable in global scope, but instantiate it in the setup() method after serial comms have been started.
How do I declare the variable, but delay instantiation?
Please post code, not pictures.
A variable is completely different from instantiating an object.
If you declare a variable this variable will be assigned the value zero if you don't assign any value at the line you declare the variable.
You can assign any value to a variable that fits into the variable at any place of your code
int myIntegerVariable; // declaration of a variable without assigning a value
void setup() {
myIntegerVariable = 123; // assigning a value to the variable
maybe you are confusing the term "variable" with something else?
best regards Stefan
I'm coming from a easier languages than C. In .NET, Java or JavaScript I would call that thing a variable (or a constant if it's declared as such). In those languages, if I declare that token, without explicitly giving it a value then the value will be whatever default is, i.e. 0 for numbers, false for booleans, null for reference types etc.
What I want is to declare the token that I would use to access the instance of CommandHandler as global, but only instantiate the object in the setup() method.
What's the correct name for that token?
In C/C++, declaring a variable assigns memory addresses to it. Whether it is initialized to some value depends on the circumstances.
I don't recall all the rules, but global numerical variables are initialized to zero. In functions, a declared, but uninitialized variable will usually contain garbage.
Consult the many on line references for the details.
Is such a thing possible?
Memory is assigned when the variable is defined. See: What's the difference between declaring and defining in C and C++ - Cprogramming.com
@ BanksySan, as already requested, post your code using Code Tags. Pictures of code are worthless.
The "Serial" object exists in global scope after you #include <Arduino.h>. It is not clear how you are trying to use it. Since the error is in "main.cpp" I suspect you forgot to #include <Arduino.h> before trying to use the names it defines.
Good to know, thanks!
Would you mind explaining when the address and value is assigned to x in this purposely incomplete code, which compiles with the expected warning, runs and prints "x = 0"?
void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
while(!Serial);
int x;
Serial.print("x = ");
Serial.println(x);
}
void loop() {}
You got lucky.
Don't rely on luck.
I DO NOT rely on luck, but this VERY PURPOSEFUL example printed x = 0. I would expect it to print garbage at other times, as mentioned in my first post.
I'm awaiting an answer on when the memory address and value is assigned.
Who knows what the optimiser has done?
Maybe crt0 blanked the stack area.
Maybe X isn't even on the stack.
What if you qualify it volatile?
Perhaps @gfvalvo will explain.
The value of an uninitialized local variable is undefined.
Have you tried declaring it outside of setup and assigning value to it inside setup?
Of course, but it has an address. When did that get assigned?
Assuming it wasn't optimized into a register or optimized away completely, memory would have been assigned when it was defined. Here:
int x;
It's never assigned a value. That's why its value is undefined.
Cool, how does that agree with your bolded statement, and the "rules" that you linked, in reply #7?
Memory is assigned when the variable is defined.
Seems to be a chicken or egg problem, which is why I am skeptical about the "rules".
So you want to declare a pointer, but instantiate the object and assign to your pointer in setup? I sense XY Problem