C++/C#跨语言编程知识点_用栈减小结构体大小和0计算偏移量_class2

视觉小萌新2024-10-22 18:56

cpp 复制代码

#include <iostream>
#define FIELDOFFSET(TYPE, MEMBER) (int)(&(((TYPE*)0)->MEMBER))
//0可以转换为任意类型的结构体或空对象

#pragma pack(push)
#pragma pack(1)
struct Info
{


	char username[10];//24-34 
	double userdata;//40-48
};
#pragma pack(pop)//会变成18
struct Frame
{
	unsigned char id;//0-1
	int width;//4-8
	long long height;//8-16
	unsigned char* data;//16-20
	Info info;//24-48
};
int main()
{
	int len2 = sizeof(Info);//子结构体改变
	int len = sizeof(Frame);//母结构体不改变
	int offset_w = FIELDOFFSET(Frame, width);
	int offset_h = FIELDOFFSET(Frame, height);
	int offset_d = FIELDOFFSET(Frame, data);
	int offset_i = FIELDOFFSET(Frame, info);
	/*len = sizeof(Info);*/
	
	return 0;
}

1.定义0计算偏移量

cpp 复制代码

#define FIELDOFFSET(TYPE, MEMBER) (int)(&(((TYPE*)0)->MEMBER))
int offset_w = FIELDOFFSET(Frame, width);

2.结构体入栈出栈

#pragma pack(push)

#pragma pack(1)

struct Info

{

char username[10];//24-34

double userdata;//40-48

..........

};

#pragma pack(pop)//会变成18