通常我們涉及到的網絡編程,也稱爲Socket編程,多數是TCP和UDP協議的編程,二者最大的區別就是:1. TCP是可靠的傳輸,需要三次握手建立連接再傳數據,而UDP是無連接的,即使沒有接收方,也可以一個勁往一個地址發數據,所以說是不可靠的傳輸模式。 2. TCP是基於流模式的,UDP是基於數據報模式的。因爲UDP比TCP稍微簡單一些,先介紹UDP編程模式。
從編程的角度來說,UDP Socket編程主要有以下幾個函數。Server端:socket()、bind()、recvfrom();Client端:socket()、sendto()。當然C/S兩端都可以收發數據的。下面給出這幾個函數的函數原型,具體細節以後再在別的系列細說。
int socket(int domain, int type, int protocol);
int bind(int sockfd, struct sockaddr *myaddr, int addrlen);
int recvfrom(int sockfd, void *buffer, size_t size, int flags, struct sockaddr *from, size_t *addrlen);
int sendto(int sockfd, void *buffer, size_t size, int flags, struct sockaddr *to, size_t *addrlen);
文末給出最基本的UDP Socket C/S模式的示例代碼,把這些代碼裏的每一個函數都理解透徹,也差不多學會了。
使用說明:
使用gcc編譯後,先執行Server程序,後執行Client程序。
Server負責接收數據,默認使用端口6666,可以使用./Server port
指定端口號。
Client負責一個勁往指定地址發送一句話,默認使用本機IP和6666端口,可以使用./Client IP port
或./Client port
指定地址和端口。
UDP Server
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#define BUFF_SIZE 200
#define DEFAULT_PORT 6666
int main(int argc, char *argv[])
{
int SERVER_PORT = DEFAULT_PORT;
if(argc > 2)
printf("param err:\nUsage: %s port | %s\n",argv[0], argv[0]);
if(argc == 2)
SERVER_PORT = atoi(argv[1]);
int servSocket, nbytes;
struct sockaddr_in servAddr, cliAddr;
int addrLen = sizeof(cliAddr);
char buffer[BUFF_SIZE];
if((servSocket = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
{
printf("socket err");
exit(1);
}
bzero(&servAddr,sizeof(servAddr));
servAddr.sin_family = AF_INET;
servAddr.sin_port = htons(SERVER_PORT);
servAddr.sin_addr.s_addr = htonl(INADDR_ANY);
if(bind(servSocket,(struct sockaddr *)&servAddr,sizeof(servAddr)) < 0)
{
printf("bind err");
exit(1);
}
printf("Listen Port: %d\nListening ...\n", SERVER_PORT);
while(1)
{
if((nbytes = recvfrom(servSocket, buffer, sizeof(buffer), 0, (struct sockaddr*)&cliAddr, &addrLen)) < 0)
{
printf("recvfrom err");
exit(1);
}
printf("\nFrom %s:%d\n", inet_ntoa(cliAddr.sin_addr), ntohs(cliAddr.sin_port));
printf("Recv: %s\nlength: %d\n\n", buffer, nbytes);
memset(buffer, 0, BUFF_SIZE);
}
}
UDP Client
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#define DEFAULT_IP "127.0.0.1"
#define DEFAULT_PORT 6666
int main(int argc, char *argv[])
{
char *SERVER_IP = DEFAULT_IP;
int SERVER_PORT = DEFAULT_PORT;
if(argc > 3)
printf("param err:\nUsage: %s ip port | %s port | %s\n",argv[0],argv[0], argv[0]);
else if(argc == 3)
{
SERVER_IP = argv[1];
SERVER_PORT = atoi(argv[2]);
}
else if(argc == 2)
SERVER_PORT = atoi(argv[1]);
struct sockaddr_in servAddr;
int cliSocket;
char *sendbuf = "Hello Server, I am Client.";
if((cliSocket = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
{
printf( "socket err");
exit(1);
}
servAddr.sin_family = AF_INET;
servAddr.sin_port = htons(SERVER_PORT);
// servAddr.sin_addr.s_addr = inet_addr(SERVER_IP); //Outdated method
inet_aton(SERVER_IP, &servAddr.sin_addr);
printf("Send data to %s:%d ...\n\n", SERVER_IP, SERVER_PORT);
while(1)
{
int num = sendto(cliSocket, sendbuf, strlen(sendbuf)+1, 0, (struct sockaddr *)&servAddr, sizeof(servAddr));
if(num == strlen(sendbuf)+1)
printf("Send: Hello Server, I am Client.\nlength:%d\n\n",num);
else
printf("send err\n");
sleep(1);
}
close(cliSocket);
return 0;
}
Source Code: https://github.com/lmshao/codebase /UdpServer.c /UdpClient.c /UdpClient_InputSend.c