二：#pragma pack()
注：如果设置的值比结构体中字节最长的类型还要大，则这个变量(注意仅针对这一个变量)只按照它的字节长度对齐，即不会出现内存浪费的情况。请参见(4)。
(1)
#pragma pack(1) //每个变量按照1字节对齐
struct A
{
char x; //aligned on byte boundary 0
int y; //aligned on byte boundary 1
}a;
sizeof(a)==5
(2)
#pragma pack(2) //每个变量按照2字节对齐
struct A
{
char x; //aligned on byte boundary 0
int y; //aligned on byte boundary 2
}a;
sizeof(a)==6
(3)
#pragma pack(4) //每个变量按照4字节对齐
struct A
{
char x; //aligned on byte boundary 0
int y; //aligned on byte boundary 4
}a;
sizeof(a)==8
(4)
#pragma pack() //默认，相当于#pragma pack(8) 每个变量按照8字节对齐
struct A
{
char x; //aligned on byte boundary 0
int y; //aligned on byte boundary 4
}a;
sizeof(a)==8
但是这里y的大小是4字节，所以不会按照8字节对齐，否则将造成1个int空间的浪费
三.#pragma comment
The following pragma causes the linker to search for the EMAPI.LIBlibrary while linking. The linker searches first in the current workingdirectory and then in the path specified in the LIB environmentvariable:
#pragma comment( lib, "emapi" )
四.#pragma deprecated
When the compiler encounters a deprecated symbol, it issues C4995:
void func1(void) {}
void func2(void) {}
int main() {
func1();
func2();
#pragma deprecated(func1, func2)
func1(); // C4995
func2(); // C4995
}
五.#pragma message
The following code fragment uses the message pragma to display a message during compilation:
#if _M_IX86 == 500
#pragma message( "Pentium processor build" )
#endif