socket通信要注意结构体的大小

panhuachun

//talker.c
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define MYPORT 5001
int main(int argc, char *argv[])
{
int sockfd;
struct sockaddr_in their_addr;
struct hostent *he;
int numbytes;
//----------------------------------------------------------------------------
// 最小字节对齐  1+8+1+1+4  =15个字节 ;attribute 对char 无效
struct aligned_test
{
char a  ;
unsigned int x[2] ;
char b;
char c;
unsigned int d ;
} __attribute__ ((packed));
// 默认排列 4 + 8 + 4(b ,c)+4  = 20个字节 //4字节对其
struct no_aligned_test
{
char a;
unsigned int x[2];
char b;
char c;
unsigned int d;
};
struct aligned_test  al_t;
struct no_aligned_test noal_t;
al_t.a='a';
al_t.x[0]=58;
al_t.x[1]=88;
al_t.b='b';
al_t.c='c';
al_t.d=236;
noal_t.a='a';
noal_t.x[0]=58;
noal_t.x[1]=99;
noal_t.b='b';
noal_t.c='c';
noal_t.d=236;
printf("sizeof(struct aligned_test)=%d\n",sizeof(struct aligned_test));
printf("sizeof(struct no_aligned_test)=%d\n",sizeof(struct no_aligned_test));
//--------------------------------------------------------------------
if (argc != 3)
{
  fprintf(stderr,"usage: talker hostname message\n");
  exit(1);
}
if ((he=gethostbyname(argv[1])) == NULL)
{  
  herror("gethostbyname");
  exit(1);
}
if((sockfd=socket(AF_INET, SOCK_DGRAM, 0)) == -1)
{
  perror ("socket");
  exit(1);
}
their_addr.sin_family = AF_INET;
their_addr.sin_port = htons(MYPORT);
their_addr.sin_addr = *((struct in_addr *)he->h_addr);
bzero(&(their_addr.sin_zero),8);
//if ((numbytes=sendto(sockfd, argv[2], strlen(argv[2]), 0,(struct sockaddr *)&their_addr, sizeof(struct sockaddr))) == -1)
if ((numbytes=sendto(sockfd, &al_t, sizeof(struct aligned_test), 0,(struct sockaddr *)&their_addr, sizeof(struct sockaddr))) == -1)
{
  perror("recvfrom");
  exit(1);
}
printf("sent %d bytes to %s\n",numbytes,inet_ntoa(their_addr.sin_addr));
close(sockfd);
return 0;
}

//listener.c

//listener.c
#include
#include
#include
#include
#include
#include
#include
#include
#define MYPORT 5001
#define MAXBUFLEN 100
main()
{
int sockfd;
int i=0;
struct sockaddr_in my_addr;
struct sockaddr_in their_addr;
int addr_len, numbytes;
struct aligned_test
{
char a  ;
unsigned int x[2] ;
char b;
char c;
unsigned int d ;
} __attribute__ ((packed));
// 默认排列 4 + 8 + 4(b ,c)+4  = 20个字节 //4字节对其
struct no_aligned_test
{
char a;
unsigned int x[2];
char b;
char c;
unsigned int d;
};
struct aligned_test  al_t;
struct no_aligned_test noal_t;
//void *buf=&al_t;
char buf[MAXBUFLEN];
char *ptr;
ptr=buf;
memset(&al_t,0,sizeof(struct aligned_test));
if((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1)
{
perror("socket");
exit(1);
}
my_addr.sin_family = AF_INET;
my_addr.sin_port = htons(MYPORT);
my_addr.sin_addr.s_addr = INADDR_ANY;
bzero(&(my_addr.sin_zero), 8);
if (bind(sockfd, (struct sockaddr *)&my_addr, sizeof(struct sockaddr)) == -1)
{
perror("bind");
exit(1);
}
addr_len = sizeof(struct sockaddr);
while(1)
{
if ((numbytes=recvfrom(sockfd, &al_t, sizeof(struct aligned_test), 0,
(struct sockaddr *)&their_addr, &addr_len)) == -1)
//if ((numbytes=recvfrom(sockfd, buf, MAXBUFLEN, 0,
//(struct sockaddr *)&their_addr, &addr_len)) == -1)
{
perror("recvfrom");
exit(1);
}
printf("got packet from %s\n",inet_ntoa(their_addr.sin_addr));
printf("packet is %d bytes long\n",numbytes);
//buf[numbytes] = '\0';
//printf("packet contains\"%s\"\n",buf);
/*
for(i=0;isizeof(struct aligned_test)=15
sizeof(struct no_aligned_test)=20
sent 15 bytes to 201.201.201.249
//listener
got packet from 201.201.201.249
packet is 15 bytes long
al_t.a=a
al_t.x[0]=58
al_t.x[1]=88
al_t.b=b
al_t.c=c
al_t.d=236



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