structurepadding.cpp

#include <iostream>

void printTypeSize() {
  std::cout << "Size of char = " << sizeof(char) << " byte" << std:: endl;
  std::cout << "Size of short = " << sizeof(short) << " byte" << std:: endl;
  std::cout << "Size of int = " << sizeof(int) << " byte" << std:: endl;
  std::cout << "Size of long = " << sizeof(long) << " byte" << std:: endl;
}

struct S1 {
  char a;   // 1 
  int b;    // 4
  char c;   // 1
  short d;  // 2
};

void printS1() {
  std::cout << "Size of S1 = 1 + 4 + 1 + 2 = " 
  << sizeof(char) + sizeof(int) + sizeof(char) + sizeof(short) << " byte, real size is "
  << sizeof(S1) << " byte" << std:: endl;
}

void printS1MemoryLayout() {
  S1 s;
  std::cout << "Address a: " << (void*)&s.a << std::endl;
  std::cout << "Address b: " << (void*)&s.b << std::endl;
  std::cout << "Address c: " << (void*)&s.c << std::endl;
  std::cout << "Address d: " << (void*)&s.d << std::endl;
}

struct S2 {
  char a;   // 1
  char c;   // 1
  short d;  // 2
  int b;    // 4
};

void printS2() {
  std::cout << "Size of S2 = 1 + 1 + 2 + 4 = " 
  << sizeof(char) + sizeof(int) + sizeof(char) + sizeof(short) << " byte, real size is "
  << sizeof(S2) << " byte" << std:: endl;
}

void printS2MemoryLayout() {
  S2 s;
  std::cout << "Address a: " << (void*)&s.a << std::endl;
  std::cout << "Address c: " << (void*)&s.c << std::endl;
  std::cout << "Address d: " << (void*)&s.d << std::endl;
  std::cout << "Address b: " << (void*)&s.b << std::endl;
}

struct S3 {
  char a;
  int b; 
};

void printS3() {
  std::cout << "Size of S3 = 1 + 4 = " 
  << sizeof(char) + sizeof(int) << " byte, real size is "
  << sizeof(S3) << " byte" << std:: endl;
}

void printS3MemoryLayout() {
  S3 s;
  std::cout << "Address a: " << (void*)&s.a << std::endl;
  std::cout << "Address b: " << (void*)&s.b << std::endl;
}

int main() {
  printTypeSize();
  printS1();
  printS1MemoryLayout();
  printS2();
  printS2MemoryLayout();
  printS3();
  printS3MemoryLayout();
}