C中的packed

packed的涵义研究

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在C中，声明结构体时可以用__attribute__ ((__packed__))来修饰，表示压缩结构体所占用的内存空间，使后一个元素紧贴钱一个元素放置。见下面的示例程序：

#include 
#include 
struct upack
{
char s;
int i;
};
struct packs
{
char s;
int i;
}__attribute__ ((__packed__));
int main(int argc, char *argv[])
{
printf("size of packs is %d and upack is %dn",sizeof(struct packs),sizeof(struct upack));
printf("size of int is %dn",sizeof(int));
printf("size of char is %dn",sizeof(char));
struct upack upk;
printf("address of upk is %dn",&upk);
printf("address of upk.s is %dn",&(upk.s));
printf("address of upk.i is %dn",&(upk.i));
struct packs pk;
printf("address of pk is %dn",&pk);
printf("address of pk.s is %dn",&(pk.s));
printf("address of pk.i is %dn",&(pk.i));
system("PAUSE"); 
return 0;
}