初学，指针问题

[mqmmx]

#include <iostream>

using namespace std;

#pragma pack(1)
typedef struct yy{
//      int a;
	char b; 
	short c; 
};

typedef unsigned char BYTE;

template<typename STRUCT>
void getbytes(const STRUCT *v, BYTE *bt)
{
	size_t size = sizeof(*v);
	//bt = (BYTE *)v;
	if ( bt == NULL)
	{
    	printf("%d\n",size);
        bt = (BYTE *)malloc(sizeof(BYTE)* size);
		//return;
		if ( bt == NULL)
		{
    	   printf("not enough memory ");
    	   return;
        }
	}

	memcpy(bt, (BYTE *)v, size);
	    
	for (int i=0; i < size; i++)
	{
		printf("%d\n",bt[i]);
		printf("%d\n",&bt[i]);
    }
}

int main()
{
	yy x;
	//x.a = 1;
	x.b = 2;
	x.c = 3;
	//BYTE* bt = (BYTE*)(&x);

	BYTE *Z = 0;
    
	//BYTE b[sizeof(x)] = {0};	
	getbytes(&x, Z);

	if ( Z == NULL)
	{
            printf("Null");
	    system("pause");
	    return 0;
        }

	for (int i=0; i < sizeof(x); i++)
	{
		//cout<<(int)b[i]<<endl;
		printf("%d\n",Z[i]);
		printf("%d\n",&Z[i]);
	}
	
	system("pause");
}

如上代码为什么指针Z没有返回值？

[ckt]

传值,你修改的z的副本，不是z本身
至于你申请空间后的操作是想做什么？

void getbytes(const STRUCT *v, BYTE** bt)
{
    size_t size = sizeof(*v);
    if ( *bt == NULL)
    {
        printf("%d\n", size);
        *bt = (BYTE *)malloc(sizeof(BYTE)* size);
        //return;
        if ( *bt == NULL)
        {
			printf("not enough memory ");
			return;
        }
    }
}

getbytes(&x, &Z);

[chmdcr]

如果想修改一级指针 请用二级指针做参数
谢谢

[chmdcr]

函数修改为
void getbytes(const STRUCT *v, BYTE **bt)形式

[mqmmx]

其实我只想要struct的BYTE数组型式返回用方法来实现，就像如下这句的结果就行了
BYTE* Z = (BYTE*)(&x);

[mmidd]

学习一下，好像是应该用二级指针做参数

[mqmmx]

多谢“吃话梅的超人”我把代码按你说的改了下，能行了，但现在有两种方法，不是哪种好些

#include <iostream>

using namespace std;

#pragma pack(1)
typedef struct yy{
//    int a;
	char b; 
	short c; 
};

typedef unsigned char BYTE;

template<typename STRUCT>
void getbytes(const STRUCT *v, BYTE **bt)
{
	size_t size = sizeof(*v);
	//*bt = (BYTE *)v;     //把这句注释去除，下面的引去结果是一样的，不知哪种写法好，更安全
        if ( *bt == NULL)
	{
    	printf("%d\n",size);
        *bt = (BYTE *)malloc(sizeof(BYTE)* size);
		//return;
		if ( *bt == NULL)
		{
    	   printf("not enough memory ");
    	   return;
        }
	}

	memcpy(*bt, (BYTE *)v, size);
	   
	for (int i=0; i < size; i++)
	{
		printf("%d\n",(*bt)[i]);
		printf("%d\n",&(*bt)[i]);
    }
}

int main()
{
	yy x;
	//x.a = 1;
	x.b = 2;
	x.c = 3;
	//BYTE* Z = (BYTE*)(&x);

	BYTE *Z = 0;
    
	//BYTE b[sizeof(x)] = {0};	
	getbytes(&x, &Z);

	if ( Z == NULL)
	{
        printf("Null");
	    system("pause");
		return 0;
    }

	for (int i=0; i < sizeof(x); i++)
	{
		//cout<<(int)b[i]<<endl;
		printf("%d\n",Z[i]);
		printf("%d\n",&Z[i]);
	}
	
	system("pause");
}