main() != loop()

Forum 2005-2010 (read only) Software Syntax & Programs
#1

Well, I understand that the subject is not a revolutionary discovery. We know about setup() and so on. But I used to believe these are similar constructions:

setup() {
  setupcode;
}
loop() {
  loopcode;
}

and

main() {
  setupcode;
  while( 1) {
    loopcode;
  }
}

But now I’ve got some doubts. It’s about the scope of variables. Here is a very simple sketch:

void setup() {
  Serial.begin(9600);
}

byte a = 0;

void loop() {
  byte b = 0;
  a ^= 1;
  b ^= 1;
  Serial.print( a, DEC);
  Serial.print( " ");
  Serial.println( b, DEC);
  delay( 1000);
}

I expected to see
1 1
0 0
1 1
0 0

and so on. Instead, I obtained:

1 1
0 1
1 1
0 1

The local variable “b” is initialized in every cycle! And, as far as I know, the local var in main() can be initialized once (if it is outside loop):

char a = 0;
int main()
{
  char b = 0;
  while(1) {
    a ^= 1;
    b ^= 1;
  }
}

Now my question to educated fellows is:

NO local variables in loop() can be initiated only once - am I right?

Thanks!

#2

This is how the generated code looks like:

include <WProgram.h>

void setup()
{
}

void loop()
{
}

int main(void)
{
  init();
  setup();
  
  for (;;)
    loop();
  
  return 0;
}

As you see from above, neither loop nor setup is in the scope of main.

#3

NO local variables in loop() can be initiated only once - am I right?

Well...

void loop() {
  static int initOnce = 5;

  Serial.println(initOnce);
  initOnce = 4;

}
#4

Thank you for answers!

So, if I add some declarations to the BenF’s code, we’ll have:

void setup()
{
}

char _global;

void loop()
{
  char _local;
  static char _static;
}

it will become

char _global;

int main(void)
{
  init();
  setup();
  
  /*static*/ char _static;
  for (;;)
    char _local;
    loop();
  
  return 0;
}

It’s very good to understand! Can you tell me, where are the rules of preprocessing Arduino (Wire) code are formally described?

And where can I find a list of compilation (linking, loading) errors?

One more question. What are the instruments of debugging Arduino sketches? Anything similar to AVR Studio? Or only with real devices?

Thanks!

#5

… not quite.

This is how it will look like:

include <WProgram.h>

void setup()
{
}

char _global;

void loop()
{
  char _local;
  static char _static;
}

int main(void)
{
  init();
  setup();
  
  for (;;)
    loop();
  
  return 0;
}
#6

Thank you! Please tell me, how can I look preprocessed program, that is passed to GCC? This example you've showed - is it just the power of your imagination or some instruments are available?

#7

I think you can simply look in the in TEMP dir, under windows it is called build768686868xxxx or something. It will contain the post processed CPP file for the sketch.

#8

You’ll find “main.cpp” in hardware/arduino/cores/arduino

#9

I think you can simply look in the in TEMP dir,

Please, where is such a directory?

#10

Somewhere in a random-folder. After Compiling, the ArduinoIDE tells you the path, written in red.

#11

Somewhere in a random-folder. After Compiling, the ArduinoIDE tells you the path, written in red.

Only shows location if you press the shift key when you verify or upload the sketch.

#12

Only shows location if you press the shift key when you verify or upload the sketch.

Cool, didn't know that (+1) :D

#13