Bool size 1bite 1 byte or 2 bytes

Projects Programming
1

I don't understand.

Some say that the bool or boolean size is one bit.

The Arduino reference says: Each bool variable occupies one byte of memory.

BUT

I ran a program to read the addresses of two booleans.

and from the addresses, I see that each one uses two bytes.

Can you help me understand which is correct?

Thank you

Antonio

2

it is no place in flash smaller as 8bit, so yes, boolean take 1 full byte in arduino platform. of course you able to pack 8 your bool variable in 1 byte and spare 7 bytes of flash

3

Thank you Kolaha.
I still don't understand why the address of one bool and another bull.
jumps by two numbers in the memory. So each one is occupying 2 bytes in the memory.
See next attachments
sketch_apr28a.ino (616 Bytes)

POINTERS TO BOOL 23-4-28
POINTERS TO BOOL 23-4-283840×2160 386 KB

2 bytes in the memory

4

What Arduino board are you using?

What is the output, for your board, from this code?

bool someBool = false;

void setup()
{
   Serial.begin(115200);
   Serial.print("the size of a bool on this board is ");
   Serial.print(sizeof(someBool));
   Serial.println(" bytes");
}

void loop()
{

}

My Uno yields:

the size of a bool on this board is 1 bytes

5

Looks like you are printing the address of a pointer to a bool, not the address of the bool itself. On an UNO a pointer is 16 bits.

bool SmplBl_1 = true;
bool *pSmplBl_1 = &SmplBl_1;

bool SmplBl_2 = true;
bool *pSmplBl_2 = &SmplBl_2;

boolean Bln_1 = false;
boolean *pBln_1 = &Bln_1;

boolean Bln_2 = false;
boolean *pBln_2 = &Bln_2;


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

void loop() {
  int AddressOfpSmplBl_1 = & pSmplBl_1;
  Serial.println(AddressOfpSmplBl_1);
  int AddressOfpSmplBl_2 = & pSmplBl_2;
  Serial.println(AddressOfpSmplBl_2);

  int AddressOfpBln_1 = & pBln_1;
  Serial.println(AddressOfpBln_1);
  
  int AddressOfpBln_2 = &pBln_2;
  Serial.println(AddressOfpBln_2);
  
  while (!Serial.available()) {
  }
  Serial.read();
}
6

Thank you, David;
You are right But if the next bool is 2 bytes apart. how can I use the adjacent byte?

7

Hello tonydg

Consider this declaration and initialization of an "array" of bits.

enum MyBits {Bit_0,Bit_1,Bit_2,Bit_3,Bit_4,Bit_5,Bit_6,Bit_7};
uint8_t myBool {0b00000000}; // start setup of bits set
void  setup()
{
}
void loop()
{
}

Simply process these bits by using

grafik

Have a nice day and enjoy coding in C++.

8

It is not two bytes apart. You were printing the address of a pointer, which occupies two bytes, not the address of a bool, which occupies one. Try the following code, note that I put the bool variables in a struct, otherwise the compiler can scatter them throughout memory at its convenience.

struct {
bool SmplBl_1 = true;
bool SmplBl_2 = true;
boolean Bln_1 = false;
boolean Bln_2 = false;
} bools;

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

void loop() {
  Serial.println((unsigned int)&bools.SmplBl_1);
  Serial.println((unsigned int)&bools.SmplBl_2);
  Serial.println((unsigned int)&bools.Bln_1);
  Serial.println((unsigned int)&bools.Bln_2);
 
  while (!Serial.available()) {
  }
  Serial.read();
}
9

in serial monitor on picture i see

int x = ....
print.sizeof(x)

INT is 2 bytes in adruino system. ESP - 4 bytes.

10

boolean and bool is the same.

11

I am aware of that, I posted the OP's original code that was attached as an .ino file in post #3.

12

I'm using Arduino uno.

13

Thank you Paul

14

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