client.c

//客户端程序：
//向服务端发送字符串，经过大小写变换后返回。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#define PORT 1234
#define MAXDATASIZE 256

int main(int argc, char *argv[])
{
	int sockfd, num;
	char buf[MAXDATASIZE];
	struct hostent *he;
	struct sockaddr_in server;

	if(argc != 2)
	{
		printf("Usage: %s <IP Address>\n", argv[0]);
		exit(1);
	}

	if((he = gethostbyname(argv[1])) == NULL)
	{
		printf("gethostbyname() error.\n");
		exit(1);
	}

	if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
	{
		printf("socket() error.\n");
		exit(1);
	}

	bzero(&server, sizeof(server));
	server.sin_family = AF_INET;
	server.sin_port = htons(PORT);
	server.sin_addr = *((struct in_addr *)he->h_addr);

	if(connect(sockfd, (struct sockaddr *)&server, sizeof(server)) == -1)
	{
		printf("connect() error.\n");
		exit(1);
	}

	//if((num = recv(sockfd, buf, MAXDATASIZE)) == -1)
	//{
		//printf("recv() error.\n");
		//exit(1);
	//}

	printf("Connected to server.\n");
	while(1){
		printf("Input:");
		//gets(buf);//dangerous
		fgets(buf, MAXDATASIZE, stdin);
		write(sockfd, buf, strlen(buf));
		if((num = read(sockfd,buf, MAXDATASIZE)) == -1){
			printf("read() error.\n");
			exit(1);
		}
		buf[num] = '\0';
		printf("Output:%s", buf);
	}

	close(sockfd);
	return 0;
}