== 서버 ==
{{{
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>
#include<arpa/inet.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<pthread.h>

#define BUFF_SIZE 1024



int thread_num[25];	//스레드 번호 (해당 스레드 활성화시 번호 값 + 1, 비활성화시 0)
			//ex) thread_num[스레드 번호]==스레드 번호+1

int client_socket_array[25];	//클라이언트 소캣, 각 스레드 마다 자신의 번호에 해당하는 소캣 사용
				//ex) 스레드가 사용 중인 소캣 == client_socket_array[스레드 번호]


char id[100][256];
char password[100][256];
char id_state[100];
int id_num;


char chat[100][BUFF_SIZE+5];
char chat_s[100], chat_e;

void* rutine(void* data)//data = &thread_num[스레드 번호]
{
	int t_num,i_num;
	int client_socket;
	char buff_rcv[BUFF_SIZE+5],buff_snd[BUFF_SIZE+5];
	int rcv;
	int i,j;

	t_num=*((int*)data);
	//사용자가 이해하기 쉽도록 스레드 번호에 +1 값을 쓰도록 한다.

	client_socket=client_socket_array[t_num-1];
	//코드의 간결화를 위해 값을 복사한다.

	recv(client_socket, buff_rcv,BUFF_SIZE,0);
	printf("%s\n",buff_rcv);
	sprintf(buff_snd,"test\n");
	send(client_socket, buff_snd, strlen(buff_snd)+1,0);
	printf("%dth client connected\n",t_num);
	//접속 검사 코드




	//로그인 루프
	recv(client_socket, buff_rcv,BUFF_SIZE,0);
	if(buff_rcv[0]=='n')//새 계정 생성
	{
		printf("client try to make ID\n");


		sprintf(buff_snd,"i\n");
		send(client_socket, buff_snd, strlen(buff_snd)+1,0);//id 요구

		recv(client_socket, buff_rcv,BUFF_SIZE,0);
		for(i=0;buff_rcv[i];i++)
			id[id_num][i]=buff_rcv[i];
		printf("%dth client's name : %s\n",t_num,buff_rcv);

		sprintf(buff_snd,"p\n");
		send(client_socket, buff_snd, strlen(buff_snd)+1,0);//password 요구

		recv(client_socket, buff_rcv,BUFF_SIZE,0);
		printf("%dth client's password : %s\n",t_num,buff_rcv);
		for(i=0;buff_rcv[i];i++)
			password[id_num][i]=buff_rcv[i];

		i_num=id_num;
		id_num++;

		printf("%dth client made new ID",t_num);

		sprintf(buff_snd,"a\n");
		send(client_socket, buff_snd, strlen(buff_snd)+1,0);//접속 확인
	}
	else
	{
		printf("client try to login\n");
		while(1)
		{			

			sprintf(buff_snd,"i\n");
			send(client_socket, buff_snd, strlen(buff_snd)+1,0);//id 요구
			recv(client_socket, buff_rcv,BUFF_SIZE,0);
			for(i=0;i<id_num;i++)
			{
				for(j=0;id[i][j];j++)
				{
					if(id[i][j]!=buff_rcv[j])
						break;
				}
				if(!id[i][j])
					break;
			}
			if(i==id_num)
				continue;
			else
				printf("%dth client's name : %s\n",t_num,buff_rcv);



			sprintf(buff_snd,"p\n");
			send(client_socket, buff_snd, strlen(buff_snd)+1,0);//password 요구
			recv(client_socket, buff_rcv,BUFF_SIZE,0);
			for(j=0;password[i][j];j++)
			{
				if(password[i][j]!=buff_rcv[j])
					break;
			}
			if(!password[i][j])
				continue;
			else
				printf("%dth client's password : %s\n",t_num,buff_rcv);

			sprintf(buff_snd,"a\n");
			send(client_socket, buff_snd, strlen(buff_snd)+1,0);//접속 확인

			i_num=i;
		}
	}


	id_state[i_num]=1;

	for(;chat_s[i_num]!=chat_e;chat_s[i_num]++)
	{
		sprintf(buff_snd,"%s\n",chat[chat_s[i_num]]);
		send(client_socket, buff_snd, strlen(buff_snd)+1,0);
	}

	while(1)
	{
		rcv=recv(client_socket,buff_rcv,BUFF_SIZE,0);
		if(rcv>0)
		{
			printf("received\n");
			sprintf(buff_snd,"%dth client : %s",num,buff_rcv);
			chat_e++;
			chat_e%=100;

			for(i=0;i<20;i++)
			{
				if(thread_num[i])
					send(client_socket_array[i],buff_snd,strlen(buff_snd)+1,0);	
			}

			for(i=0;i<id_num;i++)
			{
				if(!id_state[i])
					sprintf(chat,"%s",buff_snd);
			}
		}
		else
		{
			break;
		}
	}

	printf("disconnected\n");
	close(client_socket);
	thread_num[num-1]=0;
	client_socket_array[num-1]=0;
	//스레드가 비활성화 되었으므로 thread_num을 0으로 초기화한다.
	id_state[i_num]=0;
}

int main()
{
	int server_socket;
	pthread_t p_thread[25];
	struct sockaddr_in server_addr;
	struct sockaddr_in client_addr;
	int client_addr_size;
	int i;

	server_socket=socket(PF_INET, SOCK_STREAM, 0);
	if(server_socket==-1)
	{
		printf("socket error\n");
		exit(1);
	}


	memset(&server_addr,0,sizeof(server_addr));
	server_addr.sin_family	=AF_INET;
	server_addr.sin_port	=htons(4000);
	server_addr.sin_addr.s_addr=htonl(INADDR_ANY);
	if(-1==bind(server_socket,(struct sockaddr*)&server_addr,sizeof(server_addr)))
	{
		printf("bind error\n");
		exit(1);
	}


	printf("server started\n");

	for(i=0;i<20;i++)
		thread_num[i]=0;

	while(1)
	{
		if(-1==listen(server_socket,5))
		{
			printf("listen error\n");
			exit(1);
		}
		for(i=0;i<20;i++)
		{
			if(!thread_num[i])
			{
				client_addr_size= sizeof(client_addr);
				client_socket_array[i] = accept(server_socket, (struct sockaddr*)&client_addr,&client_addr_size);

				thread_num[i]=i+1;
				memset(&p_thread[i],0,sizeof(p_thread[i]));
				pthread_create(&p_thread[i],NULL,rutine,(void *)&thread_num[i]);
				break;
			}
		}
		if(i==20)
			printf("error : Too many clients connected");
	}
	close(server_socket);
	return 0;
}
}}}
== 클라이언트 ==
{{{
}}}