Data Structure Alignment 2

标签：packing

#include <stdio.h>


struct A{
int a;
short b;
int c;
char d;
};


struct B1{
double a;
short b;
int c;
char d;
};


#pragma pack(push,8)
struct B2{
double a;
short b;
int c;
char d;
};
#pragma pack(pop)


#pragma pack(push,4)
struct B3{
double a;
short b;
int c;
char d;
};
#pragma pack(pop)


#pragma pack(push,1)
struct B4{
double a;
short b;
int c;
char d;
};
#pragma pack(pop)


struct C{
int a;
short b[2];
char c[2];
};


int main(){
printf("A: %d\n", sizeof(struct A));
printf("B1: %d\n", sizeof(struct B1));
printf("B2: %d\n", sizeof(struct B2));
printf("B3: %d\n", sizeof(struct B3));
printf("B4: %d\n", sizeof(struct B4));
printf("C: %d\n", sizeof(struct C));


return 0;
}

For 32-bit x86:

• A char (one byte) will be 1-byte aligned.
• A short (two bytes) will be 2-byte aligned.
• An int (four bytes) will be 4-byte aligned.
• A long (four bytes) will be 4-byte aligned.
• A float (four bytes) will be 4-byte aligned.
• A double (eight bytes) will be 8-byte aligned on Windows and 4-byte aligned on Linux (8-byte with -malign-double compile time option).
• A long long (eight bytes) will be 8-byte aligned.
• A long double (ten bytes with C++Builder and DMC, eight bytes with Visual C++, twelve bytes with GCC) will be 8-byte aligned with C++Builder, 2-byte aligned with DMC, 8-byte aligned with Visual C++ and 4-byte aligned with GCC.
• Any pointer (four bytes) will be 4-byte aligned. (e.g.: char*, int*)

Data Structure Alignment 2

标签：packing

原文地址：http://blog.csdn.net/vonzhoufz/article/details/44940599