I have made a simple socket program so that client can connect to server by specifying ip of system in which server is running.
And in server we can type characters which will be received by client and client will store it in a file.
I want to clear some doubts
in server.c it shows ip address of client properly and it gives ip address of server as 0.0.0.0 . Why it is so?

How should I modify the server , so that it can have multiple clients simultaneously.

client.c

#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>  
#include <arpa/inet.h>
#include <stdio.h>
 #include<stdlib.h>
#define PORT 2080

main(int argc,char *argv[])
{
    int sock1;
    sock1 =  socket(AF_INET,SOCK_STREAM,0);
    struct sockaddr_in serv;

    serv.sin_port = htons(PORT);
    //printf("%x %x\n",PORT,htons(PORT));
    printf("%d ",argc);
    serv.sin_family = AF_INET;
    if(argc>1)
        serv.sin_addr.s_addr = inet_addr(argv[1]);
    else
    {
        printf("Plese enter a valid ip\n");
        return 1;
    }
    printf("client connecting\n");
    if(connect(sock1, (struct sockaddr *)&serv,sizeof(serv))==-1)
    {
        printf("Failed to connect\n");
        exit(1);
    }
    else
        printf("Server connection established\n");
    char buf[50];
    int i=0;
    FILE* fp = fopen("client.txt","w");
    while(1)
    {
        //printf("%d ",i);
        char c;
        //bzero(buf,sizeof(buf));
        read(sock1,&c,1);
        if(c=='`')
            break;
        //if(c!='\n')
            printf("%c",c);
        fprintf(fp,"%c",c);
        //i++;
    }
    fclose(fp);
    close(sock1);
}

server.c

#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>  
#include <arpa/inet.h>
#include <stdio.h>
 #include<stdlib.h>
#define PORT 2080

main()
{
    int sock1,sock2, clength;
    FILE *ptr;
    char c;
    char ip[40];
    sock1 =  socket(AF_INET,SOCK_STREAM,0);
    struct sockaddr_in serv,cli;
    printf("Waiting for client\n");
    serv.sin_family = AF_INET;
    serv.sin_port = htons(PORT);
    serv.sin_addr.s_addr = htonl(INADDR_ANY);
    bind(sock1,(struct sockaddr *)&serv, sizeof(serv));
    listen(sock1,5);
    clength = sizeof(cli);
    sock2 = accept(sock1,(struct sockaddr *)&cli,&clength);
    printf("\n Client Connected\n");
    inet_ntop(AF_INET,(void *)&(cli.sin_addr),ip,clength);
    printf("\nClient IP :%s ",ip);
    inet_ntop(AF_INET,(void *)&(serv.sin_addr),ip,sizeof(serv));
    printf("\nServer IP :%s ",ip);
    while(1)
    {
        printf("\nEnter char : ");
        scanf("%c",&c);
        printf("%c",c);
        write(sock2,&c,1);
        if(c=='`')
            break;
    }
    close(sock2);
    close(sock1);
    return 0;
}

what exacltly you are trying to ask ? Do you want changes in this program or you want to correct ? i mean this code has error or this has to update ?

I have two issue
1. server program shows client ip properly. But it shows server ip as 0.0.0.0 . I want to know why it is happening.
2. I want to modify the program so that it can have multiple clients simultaneously.

I hope things are clear now.

For multiple connections you need to do these things :

  1. Putting accept statement and the code in an infinite loop.

  2. After a connection is established, you need to call fork() to for a new process.

  3. The child process will close sockfd and call doprocessing() function, passing the new socket file descriptor as an argument. When the two processes have completed their conversation, as indicated by doprocessing() returning, this process simply exits.

  4. The parent process closes newsockfd. Because all of this code is in an infinite loop, it then returns to accept statement for another connection.

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