Difference in the output between the C code and the Arduino IDE-CodePudding

Why there is difference in the output between the C code and the Arduino IDE ? The output of this c code =16

typedef struct str
{  
  int* array; 
  int y;
  int z;
} str;

void neww() {
 printf("str=%d\n",sizeof(str));  //
}

void main(){
  neww();
}

And when run it on esp32 I get on output =12 !!! why?! This is the code of Arduino IDE

typedef struct str
{  
  int* array; 
  int y;
  int z;
} str;

void neww() {
 printf("str=%d\n",sizeof(str));  //
}

void setup(){
  Serial.begin(115200); 
  delay(500);
  neww();
}
void loop(){}

CodePudding user response：

I will simplify your problem:

In your computer:

int *int_pointer;
printf("Size of int_pointer: %d", sizeof(int_pointer)); // Output: 8

In your ESP32:

int *int_pointer;
printf("Size of int_pointer: %d\n", sizeof(int_pointer)); // Output: 4

That is the difference.

A pointer stores a memory address so its size will be (at least) the same as the size of an address in its respective processor.

Your computer is a 64-bit system -> The size of each address is 8 bytes -> The pointer needs to have 8 bytes to be able to store it.
Your ESP32 is a 32-bit system -> The size of each address is 4 bytes -> The pointer only needs to have 4 bytes to be able to store it.

CodePudding user response：

This stuct

typedef struct str
{  
  int* array; 
  int y;
  int z;
} str;

contains a pointer (int * array). The size of pointers depends on where the code is running. On a 32 bit machine they will be 4 bytes, on a 64 bit machine 8. There can be other sizes to (2 - pdp 11, 6 - some mainframes)

So the sizeof operator will return different values on different systems