sizeof和new的开销空间

选自：《编程珠玑第二版》附录3

/* Copyright (C) 1999 Lucent Technologies */
/* From 'Programming Pearls' by Jon Bentley */

/* spacemod.cpp -- simple model for C++ space */

#include 
using namespace std;

#define MEASURE(T, text) {					\
	cout << text << "\t";					\
	cout << sizeof(T) << "\t";				\
	int lastp = 0;							\
	for (int i = 0; i < 11; i++) {			\
		T *p = new T;						\
		int thisp = (int) p;				\
		if (lastp != 0)						\
			cout << " " << thisp - lastp;	\
		lastp = thisp;						\
	}										\
	cout << "\n";							\
}

// Must use macros; templates give funny answers

template 
void measure(char *text)
{	cout << " measure: " << text << "\t";
	cout << sizeof(T) << "\n";
}

struct structc { char c; };
struct structic { int i; char c; };
struct structip { int i; structip *p; };
struct structdc { double d; char c; };
struct structcd { char c; double d; };
struct structcdc { char c1; double d; char c2; };
struct structiii { int i1; int i2; int i3; };
struct structiic { int i1; int i2; char c; };
struct structc12 { char c[12]; };
struct structc13 { char c[13]; };
struct structc28 { char c[28]; };
struct structc29 { char c[29]; };
struct structc44 { char c[44]; };
struct structc45 { char c[45]; };
struct structc60 { char c[60]; };
struct structc61 { char c[61]; };

int main()
{	cout << "Raw sizeof";
	cout << "\nsizeof(char)="     << sizeof(char);	
	cout << "  sizeof(short)="    << sizeof(short);
	cout << "  sizeof(int)="      << sizeof(int);
	cout << "\nsizeof(float)="    << sizeof(float);
	cout << "  sizeof(struct *)=" << sizeof(structc *);
	cout << "  sizeof(long)="     << sizeof(long);
	cout << "\nsizeof(double)="   << sizeof(double);

	cout << "\n\nMEASURE macro\n";
	MEASURE(int, "int");
	MEASURE(structc, "structc");
	MEASURE(structic, "structic");
	MEASURE(structip, "structip");
	MEASURE(structdc, "structdc");
	MEASURE(structcd, "structcd");
	MEASURE(structcdc, "structcdc");
	MEASURE(structiii, "structiii");
	MEASURE(structiic, "structiic");
	MEASURE(structc12, "structc12");
	MEASURE(structc13, "structc13");
	MEASURE(structc28, "structc28");
	MEASURE(structc29, "structc29");
	MEASURE(structc44, "structc44");
	MEASURE(structc45, "structc45");
	MEASURE(structc60, "structc60");
	MEASURE(structc61, "structc61");

	
	cout << "\nmeasure template (strange results)\n";
	// Uncomment below lines to see answers change
	measure("int");
//	measure("structc");
//	measure("structic");
	return 0;
}

作者给某结构类型指针连续分配内存，用地址相减得出该结构类型的new的开销空间。

注意：

1、sizeof(T*)，T*是指针，则大小都是4个字节（32位计算机）；//  WIN32 XP

2、sizeof(T)，T是结构类型，则大小都是该结构类型的空间大小（静态）；//不知道怎么叙述，呵呵。

3、给某结构类型指针连续分配内存，用地址相减得出该结构类型的new的开销空间，该大小一般大于该结构类型的空间大小（静态），且有一定对齐规律性；