------------------------------------------------------------------
# vi  receive_socket.c
-----------------------------------------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define SERV_TCP_PORT 9090
#define SERV_ADDR "127.0.0.1"
int main()
{
        int x;
        struct sockaddr_in  serv_addr;
        char buf[50];
        printf("Hi, I am the client\n");
        bzero((char *) &serv_addr, sizeof(serv_addr));
        serv_addr.sin_family = PF_INET;
        serv_addr.sin_addr.s_addr = inet_addr(SERV_ADDR);
        serv_addr.sin_port = htons(SERV_TCP_PORT);
        /* open a tcp socket*/
        if ( (x =socket(PF_INET, SOCK_STREAM,0)) < 0)
        {
              printf("socket creation error\n");
              exit(1);
        }
        printf(" socket opened successfully. socket num is %d\n", x);
        /* connect to  the server */
        if (connect(x, (struct sockaddr *) &serv_addr, sizeof(serv_addr))<0)
        {
              printf("can't connect to the server\n");
              exit(1);
        }
        /* send input str to the server */
        printf("now i am connected to the erver. enter a string to send\n");
scanf("%s", buf);
        write(x,buf,strlen(buf));
          printf("now let's read from the server\n");

read(x,buf,50);
        buf[10]=0;
        printf("what echoed from the server is %s\n",buf);
}

-----------------------------------------------------------------
# vi  send_socket.c
-------------------------------------------------------------------
#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>

#define SERV_TCP_PORT 9090 
#define SERV_ADDR "127.0.0.1"

int main()
{
        int s1,s2,x;
        struct sockaddr_in serv_addr;
        struct sockaddr_in cli_addr;
        char buf[20];
        int xx;
        printf("Hi, I am the server\n");
        bzero((char *)&serv_addr, sizeof(serv_addr));
        serv_addr.sin_family=AF_INET;
        serv_addr.sin_addr.s_addr=inet_addr(SERV_ADDR);
        serv_addr.sin_port=htons(SERV_TCP_PORT);
        if((s1=socket(PF_INET, SOCK_STREAM, 0))<0)
        {
                printf("socket creation error\n");
                exit(1);
        }
        printf("socket created successfully. socket num is %d\n", s1);
        x=bind(s1, (struct sockaddr *)&serv_addr, sizeof(serv_addr));
        if (x < 0)
        {
                printf("binding failed\n");
                exit(1);
        }
        printf("binding passed\n");
        listen(s1, 5);
        xx = sizeof(cli_addr);
        s2 = accept(s1,(struct sockaddr*)&cli_addr,&xx);
        printf("we passed accept. new socket num is %d\n", s2);
        read(s2,buf,10);
        buf[10]=0;
        printf("we got %s from cli\n",buf);
        printf("what do you want to send to cli? enter your string\n");
        scanf("%s", buf);
        write(s2,buf,strlen(buf));
        exit(0);
}

--------------------------------------------------------------
compile  하기
------------------------------------------------------------
# gcc  -o  receive  receive_socket.c
# gcc  -o  send  send_socket.c
---------------------------------------------------------

<  실행 방법 >
#  ./receive
    대기하고 있음
# ./send

#