MemAlign内存对齐

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本文通过C++代码示例介绍了内存对齐的概念及其对结构体成员变量内存布局的影响。展示了不同编译指令下结构体大小的变化，并通过具体实例分析了成员变量的偏移量，有助于理解内存对齐在实际编程中的应用。

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// MemAlign.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

struct MyStruct 
{ 
double dda1; 
char dda; 
int type;
}; 

#pragma pack(push) //保存对齐状态 
#pragma pack(4)//设定为4字节对齐 
struct Test 
{ 
char m1; 
double m4; 
int m3; 
}; //0,4~11,12~15....16
#pragma pack(pop)//恢复对齐状态 

struct MyStruct2 
{ 
	char dda; 
	double dda1; 
	int type;

};

int memoffset(void* pa,void* pb)
{
	return (char*)pb-(char*)pa;
}

int main(int argc, char* argv[])
{
	MyStruct  obj;
	printf("int size:%d\n",sizeof(int));//4
	printf("char size:%d\n",sizeof(char));//1
	printf("double :%d\n",sizeof(double));//8
	printf("MyStruct size:%d\n",sizeof(MyStruct));//4+4+8=16
	{
		printf("obj:%x,obj->dda1 :%x,offset:%d\n",&obj,&obj.dda1, memoffset(&obj,&(obj.dda1)) );//0
		printf("obj:%x,obj->dda :%x,offset:%d\n",&obj,&obj.dda,memoffset(&obj,&(obj.dda)));//8
		printf("obj:%x,obj->type :%x,offset:%d\n",&obj,&obj.type,memoffset(&obj,&(obj.type)));//12
	}
	MyStruct2  obj2;
	printf("MyStruct2 size:%d\n",sizeof(MyStruct2));//0,8,16......8+8+4=20?24!
	{
		printf("obj2:%x,obj2->dda :%x,offset:%d\n",&obj2,&obj2.dda,memoffset(&obj2,&(obj2.dda)));//
		printf("obj2:%x,obj2->dda1 :%x,offset:%d\n",&obj2,&obj2.dda1, memoffset(&obj2,&(obj2.dda1)) );//		
		printf("obj2:%x,obj2->type :%x,offset:%d\n",&obj2,&obj2.type,memoffset(&obj2,&(obj2.type)));//

	}
///////////////////////////
	Test objtest;
	printf("Test size:%d\n",sizeof(Test));////0,4~11,12~15....16
	{
		printf("objtest:%x,objtest->m1 :%x,offset:%d\n",&objtest,&objtest.m1,memoffset(&objtest,&objtest.m1));//
		printf("objtest:%x,objtest->m4 :%x,offset:%d\n",&objtest,&objtest.m4, memoffset(&objtest,&objtest.m4) );//		
		printf("objtest:%x,objtest->m3 :%x,offset:%d\n",&objtest,&objtest.m3,memoffset(&objtest,&objtest.m3));//

	}

	return 0;
}

/*
int size:4
char size:1
double :8
MyStruct size:16
obj:12ff70,obj->dda1 :12ff70,offset:0
obj:12ff70,obj->dda :12ff78,offset:8
obj:12ff70,obj->type :12ff7c,offset:12
MyStruct2 size:24
obj2:12ff58,obj2->dda :12ff58,offset:0
obj2:12ff58,obj2->dda1 :12ff60,offset:8
obj2:12ff58,obj2->type :12ff68,offset:16
Test size:16
objtest:12ff48,objtest->m1 :12ff48,offset:0
objtest:12ff48,objtest->m4 :12ff4c,offset:4
objtest:12ff48,objtest->m3 :12ff54,offset:12
Press any key to continue
*/