4.9 sizeof运算符

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书中页数：P139
代码名称：arraysizeof.cc sizeof_pgm.cc

//arraysizeof.cc 
#include <iostream>
using std::cout; using std::endl;

#include <cstddef>
using std::size_t;

int ia[] = {0,1,2,3,4,5,6,7,8,9};

int main()
{
   // sizeof(ia)/sizeof(*ia) returns the number of elements in ia
   constexpr size_t sz = sizeof(ia)/sizeof(*ia);

   int arr2[sz];  // ok sizeof returns a constant expression 

   cout << "ia size: " << sz << endl;

   return 0;
}

//sizeof_pgm
#include <iostream>
using std::cout; using std::endl;

#include "Sales_data.h"

int main() 
{
	Sales_data data, *p;
	sizeof(Sales_data); // size required to hold an object of type Sales_data 
	sizeof data; // size of data's type, i.e., sizeof(Sales_data)
	sizeof p;    // size of a pointer
	sizeof *p;   // size of the type to which p points, i.e., sizeof(Sales_data)
	sizeof data.revenue; // size of the type of Sales_data's revenue member 
	sizeof Sales_data::revenue; // alternative way to get the size of revenue
	
	cout << "short: " << sizeof(short) << "\n"
	     << "short[3]: " << sizeof(short[3]) << "\n"
	     << "short*: " << sizeof(short*) << "\n"
	     << "short&: " << sizeof(short&) << endl;
	
	cout << endl; 
	
	cout << "int: " << sizeof(int) << "\n"
	     << "int[3]: " << sizeof(int[3]) << "\n"
	     << "int*: " << sizeof(int*) << "\n"
	     << "int&: " << sizeof(int&) << endl;
	
	cout << endl; 
	
	cout << "Sales_data: " << sizeof(Sales_data) << "\n"
	     << "Sales_data[3]: " << sizeof(Sales_data[3]) << "\n"
	     << "Sales_data*: " << sizeof(Sales_data*) << "\n"
	     << "Sales_data&: " << sizeof(Sales_data&) << endl;
	
	cout << "Sales_data::revenue: " << sizeof Sales_data::revenue << "\n"
	     << "data.revenue: " << sizeof data.revenue << endl;

	int x[10];   
	int *ip = x;

	// number of elements in x
	cout << sizeof(x)/sizeof(*x) << endl;

	// divides sizeof a pointer by sizeof an int
	cout << sizeof(ip)/sizeof(*ip) << endl;
	
	return 0;
}