socket编程——一个简单的例子

转载自：http://blog.csdn.net/wind19/article/details/6156339

从一个简单的使用TCP例子开始socket编程，其基本步骤如下：

server                                                  client

 

+++++++                                          ++++++++

创建socket                                          创建socket

+++++++                                          ++++++++

      |                                                         |

      |                                                         |

      |                                                         |

+++++++                                          ++++++++

地址赋值（                                           地址赋值（

自己的地址）                                        服务器地址）

+++++++                                          ++++++++

      |                                                         |

      |                                                         |

      |                                                         |

++++++++                                              |

用bind绑定                                                |

socket和地址                                             |

++++++++                                              |

      |                                                         |

      |                                                         |

      |                                                         |

+++++++                                                 |

listen                                                         |

+++++++                                                  |

      |                                                    ++++++++++

      |   <------------------------------          connect 服务器         

      |                                                    ++++++++++

+++++++                                                  |

accept                                                        |

+++++++                                                  |

      |                                                           |

      |                                                    +++++++++

      |                                                     recv 和send

      |                                                     进行数据处理

      |                                                     +++++++++

+++++++++                                                |

用accept得到                                                 |

的socket进行                                                 |

recv 和 send                                                 |

+++++++++                                                |

      |                                                             |

      |                                                             |

      |                                                             |

+++++++++                                        +++++++++

close socket                                         close socket

+++++++++                                        +++++++++

 

根据以上步骤，服务器端的代码为

从一个简单的使用TCP例子开始socket编程，其基本步骤如下：

server                                                  client

+++++++                                          ++++++++

创建socket                                          创建socket

+++++++                                          ++++++++

|                                                         |

|                                                         |

|                                                         |

+++++++                                          ++++++++

地址赋值（                                           地址赋值（

自己的地址）                                        服务器地址）

+++++++                                          ++++++++

|                                                         |

|                                                         |

|                                                         |

++++++++                                              |

用bind绑定                                                |

socket和地址                                             |

++++++++                                              |

|                                                         |

|                                                         |

|                                                         |

+++++++                                                 |

listen                                                         |

+++++++                                                  |

|                                                    ++++++++++

|   <------------------------------          connect 服务器

|                                                    ++++++++++

+++++++                                                  |

accept                                                        |

+++++++                                                  |

|                                                           |

|                                                    +++++++++

|                                                     recv 和send

|                                                     进行数据处理

|                                                     +++++++++

+++++++++                                                |

用accept得到                                                 |

的socket进行                                                 |

recv 和 send                                                 |

+++++++++                                                |

|                                                             |

|                                                             |

|                                                             |

+++++++++                                        +++++++++

close socket                                         close socket

+++++++++                                        +++++++++

根据以上步骤，服务器端的代码为

客户端代码为：

#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <syslog.h>
#include <errno.h>
#include <stdlib.h>
#define MAX_LISTEN_NUM 5
#define SEND_BUF_SIZE 100
#define RECV_BUF_SIZE 100
#define SERVER_PORT 1010
int main()
{
int sock_fd = 0;
char recvbuf[RECV_BUF_SIZE] = {0};
char sendbuf[SEND_BUF_SIZE] = {0};
int recvlen = 0;
int retlen = 0;
int sendlen = 0;
int leftlen = 0;
char *ptr = NULL;
struct sockaddr_in ser_addr;

memset(&ser_addr, 0, sizeof(ser_addr));
ser_addr.sin_family = AF_INET;
inet_aton("127.0.0.1", (struct in_addr *)&ser_addr.sin_addr);
ser_addr.sin_port = htons(SERVER_PORT);
sock_fd = socket(AF_INET, SOCK_STREAM, 0);
if(sock_fd < 0)
{
syslog(LOG_ERR, "%s:%d, create socket failed", __FILE__, __LINE__);
exit(1);
}
if(connect(sock_fd, (struct sockaddr *)&ser_addr, sizeof(ser_addr)) < 0)
{
syslog(LOG_ERR, "%s:%d, connect socket failed", __FILE__, __LINE__);
exit(1);
}
//receive data
recvlen = 0;
retlen = 0;
ptr = recvbuf;
leftlen = RECV_BUF_SIZE -1;
//do
{
retlen = recv(sock_fd, ptr, leftlen, 0) ;
if(retlen < 0)
{
if(errno == EINTR)
retlen = 0;
else
exit(1);
}
recvlen += retlen;
leftlen -= retlen;
ptr += retlen;
}
//while(recvlen && leftlen);
printf("receive data is : %s", recvbuf);
sprintf(sendbuf, "hello server/n");
//send data
sendlen = strlen(sendbuf) +1;
retlen = 0;
leftlen = sendlen;
ptr = sendbuf;
// while(leftlen)
{
retlen = send(sock_fd, ptr, sendlen, 0);
if(retlen < 0)
{
if(errno == EINTR)
retlen = 0;
else
exit(1);
}
leftlen -= retlen;
ptr += retlen;
}
close(sock_fd);

}


现在一个简单的使用tcp的socket通信的例子已经完成了，这里有几个需要说明的问题

1）头文件：

sys/socket.h   包含了socket相关的函数，如socket，send 和recv， 以及struct sockaddr等

netinet/in.h    包含了地址结构，如struct sockaddr_in

errno.h           包含了errno 和 EINTR

syslog.h         包含了syslog相关的信息，其打印结果在/var/log/messages里面

 

2）socket地址

对于IPv4来说，其地址用的是struct sockaddr_in，具体结构如下

struct in_addr {
in_addr_t s_addr; /* 32-bit IPv4 address */
/* network byte ordered */
};

struct sockaddr_in {
uint8_t sin_len; /* length of structure (16) */
sa_family_t sin_family; /* AF_INET */
in_port_t sin_port; /* 16-bit TCP or UDP port number */
/* network byte ordered */
struct in_addr sin_addr; /* 32-bit IPv4 address */
/* network byte ordered */
char sin_zero[8]; /* unused */
};

其中sin_len我们一般不关注，也不填（只有在使用routing socket的时候才用到，被内核用来处理各种协议簇的地址结构）。bind, connect, sendto, 和 sendmsg会把socket地址从程序传递给内核； 而accept, recvfrom, recvmsg, getpeername, 和 getsockname会把地址从内核传递给程序。因为不同协议簇的地址结构是不一样的，所以必须要有一个通用的指针来传递地址，对于ANSI C来说我们一般使用void *，但是socket产生早于ANSI C，所以也就没有使用这个机制，而是使用一个通用的地址结构struct sockaddr来处理的