Linux socket programming client model (using getaddrinfo)

#include "unistd.h"#include "sys/types.h"#include "sys/socket.h"#include "netinet/in.h"#include "arpa/inet.h"#include "stdio.h"#include "string.h"#include 
 
  #include 
  
   #include 
   
    #include 
    
     void error(int status, int err,char *fmt, ...) {        va_list ap; va_start(ap, fmt); vfprintf(stderr, fmt, ap);        va_end(ap); if(err)  fprintf(stderr,":%s(%d)/n",strerror(err),err);        if(status)    exit(status);}          int  client_connect(const char *hostname,const char *service,struct sockaddr_in *server,const char *protocol,int flag){  int sockfd,err;  struct addrinfo hints,*res,*r;  bzero(&hints,sizeof(struct addrinfo));  hints.ai_family=AF_INET;    if(strcmp(protocol,"udp")==0)   hints.ai_socktype=SOCK_DGRAM;  else if(strcmp(protocol,"tcp")==0)   hints.ai_socktype=SOCK_STREAM;  err=getaddrinfo(hostname,service,&hints,&res);    if(err){   printf("%s/n",gai_strerror(err)); exit(0);  }  for( r = res; r; r = r->ai_next) {   if((sockfd=socket(r->ai_family,r->ai_socktype,r->ai_protocol))<0)  continue; if((r->ai_socktype==SOCK_DGRAM)&&(flag==0))  break; if((((r->ai_socktype==SOCK_DGRAM)&&(flag==1))||(r->ai_socktype==SOCK_STREAM))&&(connect(sockfd,r->ai_addr,r->ai_addrlen)==0))  break; close(sockfd);  }    if(r==NULL)   error(1,0,"connect error!!/n"); memcpy(server,(struct sockaddr_in *)r->ai_addr,r->ai_addrlen); freeaddrinfo(res); return sockfd;  }//tcpclient.c#include 
     
      #include 
      
       #include 
       
        #include 
        
         #include 
         
          #include 
          
           #include 
           
            #include 
            
             void process_client(int s) { char buff[128]; int rc,maxfd; fd_set rset; FD_ZERO(&rset); while(1) { FD_SET(s,&rset); FD_SET(0,&rset); maxfd=s+1; if(select(maxfd,&rset,NULL,NULL,NULL)==-1) error(1,0,"select error!"); if(FD_ISSET(s,&rset)) { rc = recv(s,buff,sizeof(buff),0); if(rc <= 0) break; buff[rc]='/0'; write(1,buff,rc); } if(FD_ISSET(0,&rset)) { if(fgets(buff,sizeof(buff),stdin)==NULL) shutdown(s,SHUT_WR); send(s,buff,strlen(buff),0); } } /* while(fgets(buff,sizeof(buff),stdin)!=NULL) { send(s,buff,strlen(buff),0); rc = recv(s,buff,sizeof(buff),0); if(rc <= 0) break; buff[rc]='/0'; write(1,buff,rc); bzero(buff,sizeof(buff)); } */}int main(int argc, char **argv) { struct sockaddr_in server,temp; char *hname, *sname; int s, c, len; if(argc < 2) error(1,0,"parameters less than 2/n"); else if(argc == 2) { hname = NULL; sname = argv[1]; } else if(argc == 3) { hname = argv[1]; sname = argv[2]; } s = client_connect(hname, sname, &server, "tcp",0); len=sizeof(temp); getsockname(s,(struct sockaddr *)&temp,&len); printf("local %s:%d/n",inet_ntoa(temp.sin_addr),ntohs(temp.sin_port)); getpeername(s,(struct sockaddr *)&temp,&len); printf("remote %s:%d/n",inet_ntoa(temp.sin_addr),ntohs(temp.sin_port)); process_client(s); close(s); exit(0);}