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class A
{
union u
{
char buffer[13];
int i;
}u;
void foo(){}
typedef char * (*f)(void*);
enum{red,green,blue} color;
}a;
/*************************************************************************
> File Name: a.cpp
> Author: 傻李
> Mail: hellojukay@gmail.com
> Created Time: 2014年11月16日 星期日 11时36分41秒
************************************************************************/
#include<iostream>
using namespace std;
int main()
{
class A
{
union u
{
char buffer[13];
int i;
}u;
void foo(){}
typedef char * (*f)(void*);
enum{red,green,blue} color;
}a;
cout << sizeof(a);
return 0;
}
#include <iostream>
using namespace std;
int main() {
class obj
{
}a;
cout<< sizeof(a);
// your code goes here
return 0;
}
这个输出1,怎么解释呢[/quote]
c++ 要求所有完整对象的大小必需为正整数(不包括零),对于空类,1 是满足 c++ 标准的最小数字。char buffer[12];
输出结果就是16了,很不理解啊[/quote]
搜索一下字节对齐就懂了[/quote]#include <iostream>
using namespace std;
int main() {
class obj
{
int a;
char b;
}a;
cout<< sizeof(a);
// your code goes here
return 0;
这个结果是8,貌似不需要对齐吧#include <iostream>
using namespace std;
int main() {
class obj
{
}a;
cout<< sizeof(a);
// your code goes here
return 0;
}
这个输出1,怎么解释呢#include <stdio.h>
#define field_offset(s,f) (int)(&(((struct s *)(0))->f))
struct AD { int a; char b[13]; double c;};
#pragma pack(push)
#pragma pack(1)
struct A1 { int a; char b[13]; double c;};
#pragma pack(2)
struct A2 { int a; char b[13]; double c;};
#pragma pack(4)
struct A4 { int a; char b[13]; double c;};
#pragma pack(8)
struct A8 { int a; char b[13]; double c;};
#pragma pack(16)
struct A16 { int a; char b[13]; double c;};
#pragma pack(pop)
int main() {
printf("AD.a %d\n",field_offset(AD,a));
printf("AD.b %d\n",field_offset(AD,b));
printf("AD.c %d\n",field_offset(AD,c));
printf("\n");
printf("A1.a %d\n",field_offset(A1,a));
printf("A1.b %d\n",field_offset(A1,b));
printf("A1.c %d\n",field_offset(A1,c));
printf("\n");
printf("A2.a %d\n",field_offset(A2,a));
printf("A2.b %d\n",field_offset(A2,b));
printf("A2.c %d\n",field_offset(A2,c));
printf("\n");
printf("A4.a %d\n",field_offset(A4,a));
printf("A4.b %d\n",field_offset(A4,b));
printf("A4.c %d\n",field_offset(A4,c));
printf("\n");
printf("A8.a %d\n",field_offset(A8,a));
printf("A8.b %d\n",field_offset(A8,b));
printf("A8.c %d\n",field_offset(A8,c));
printf("\n");
printf("A16.a %d\n",field_offset(A16,a));
printf("A16.b %d\n",field_offset(A16,b));
printf("A16.c %d\n",field_offset(A16,c));
printf("\n");
return 0;
}
//AD.a 0
//AD.b 4
//AD.c 24
//
//A1.a 0
//A1.b 4
//A1.c 17
//
//A2.a 0
//A2.b 4
//A2.c 18
//
//A4.a 0
//A4.b 4
//A4.c 20
//
//A8.a 0
//A8.b 4
//A8.c 24
//
//A16.a 0
//A16.b 4
//A16.c 24
//
//
char buffer[12];
输出结果就是16了,很不理解啊char buffer[12];
输出结果就是16了,很不理解啊[/quote]
搜索一下字节对齐就懂了