Hi all,
I’m 95% sure this is something dumb that I’ve done, but I’ve been stuck for days. I should note that I haven’t written any C++ in about twenty years so the odds that this is a syntax issue are pretty high – I just cannot see it for the life of me.
With the disclaimer out of the way… here’s the problem code. I’ve boiled it down to the bare necessities to illustrate:
#include "Serial.h"
ServicePortSerial sp;
bool flipped = true;
//----------------------------------------------------------------
// SETUP
//----------------------------------------------------------------
void setup() {
sp.begin();
}
//----------------------------------------------------------------
// MAIN LOOP
//----------------------------------------------------------------
void loop() {
byte foo;
bool cond = true;
sp.print("flipped: ");
sp.println(flipped);
if( !(flipped) ) {
sp.println("I SHOULD NOT BE HERE"); // this does not execute
foo = 99; // this excecutes
}
sp.print("foo:");
sp.println(foo);
}
For this setup, the console outputs:
flipped: 1
foo:99
What’s happening is that the setting of “foo” inside the if statement happens whether flipped is set or not BUT the print statement inside there does not fire. I would expect that the print statement doesn’t fire and “foo” remains set at zero.
If I change the code to check the value of the locally declared “cond” rather than “flipped” then it works as expected.
e.g.
if( !cond ) {
sp.println("I SHOULD NOT BE HERE");
foo = 99; // this doesn't execute
}
So the question boils down to:
- The value of the local and the global are the same
- I have traced out cond==flipped and it evaluates true
- Why (this is the bit that is frying my noodle) does the assignment of foo execute but not the println?
- did I do something overtly stupid or am I being screwed by the compiler?
thanks!
-O
GCC does not zero out local variables so “byte foo;” starts out with whatever value the memory address it is in had originally which happens to be… 99.