指针作为形参传递值

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct  gvr_pdu
{
   int  uiLength;      
   char   *pucContent;    
}Gvr_pdu;

typedef enum {
  UID_CNTRL = 0,
  UID_BPDU
} UID_CMD_TYPE_T;

typedef enum {
  UID_PORT_CONNECT,
  UID_PORT_DISCONNECT,
  UID_BRIDGE_SHUTDOWN,
  UID_BRIDGE_HANDSHAKE,
  UID_LAST_DUMMY
} UID_CNTRL_CMD_T;

typedef struct uid_port_control_s {
  UID_CNTRL_CMD_T cmd;
  unsigned long  param1;  
  unsigned long  param2;  
} UID_CNTRL_BODY_T;

typedef struct uid_msg_header_s {
  UID_CMD_TYPE_T    cmd_type;
  long          sender_pid;
  int           destination_port;
  int           source_port;
  int        body_len;
} UID_MSG_HEADER_T;

typedef struct uid_msg_s {
  UID_MSG_HEADER_T  header;
  union {
    UID_CNTRL_BODY_T    cntrl;
    char *bpdu ;
  } body;

} UID_MSG_T;

void test(UID_MSG_T *msg)
{
int port_no;
int i;
Gvr_pdu sGvrpPud ={0} ;

for(i=0;i<sGvrpPud.uiLength;i++){
printf("puc[%d]:%d\n",i,msg->body.bpdu[i]);
}

port_no = msg->header.source_port;
sGvrpPud.uiLength = msg->header.body_len ;
printf("port num:%d \t uiLength:%d\n",port_no,sGvrpPud.uiLength);
memcpy(&sGvrpPud.pucContent,msg->body.bpdu,sGvrpPud.uiLength);
for(i=0;i<sGvrpPud.uiLength;i++){
printf("puc[%d]:%d\n",i,sGvrpPud.pucContent[i]);
}
}

int main()
{
char buff[sizeof(UID_MSG_T)];
UID_MSG_T *msg =(UID_MSG_T *)malloc(sizeof(UID_MSG_T));
msg->body.bpdu =(char *)malloc(sizeof(UID_MSG_T));
UID_MSG_T *temp;
char str[100]={0};
int i,n=0;

for(i=0;i<sizeof(UID_MSG_T);i++){
buff[i]=i;
}

printf("buff length:%d\n",strlen(buff));
msg->header.sender_pid = 100;
msg->header.cmd_type =UID_BPDU;
msg->header.source_port=1;
msg->header.body_len=sizeof(UID_MSG_T);
memcpy(msg->body.bpdu,buff,sizeof(UID_MSG_T));

        for(i=0;i<sizeof(UID_MSG_T);i++){
printf("%d\n",msg->body.bpdu[i]);
}
test(msg);

        free(msg->body.bpdu);
free(msg);
return 0;
}

在函数test中把结构体msg作为形参，在函数内输出msg->body.bpud的值为什么会不存在？
怎么才能实现msg->body.bpdu的值赋给sGvrpPud.pucContent 指针 C
[解决办法]
sGvrpPud.uiLength 没值？