linux - C Socket program example - Error on binding: Already in use -

i have following example code using linux sockets:

void serve_request(int newsockfd) {     char buffer[256];     int n;        /*if connection established start communicating*/     bzero(buffer, 256);     n=read(newsockfd, buffer, 255);     if(n<0)     {            perror("error reading socket");     }     printf("here message: %s\n",buffer);      /*write response client*/     n=write(newsockfd,"i got message", 18);     if(n<0)     {         perror("error writing socket");         exit(1);     }     //close(newsockfd); }  int main(int argc, char* argv) {     int sockfd, newsockfd, portno, clilen;     char buffer[256];     struct sockaddr_in serv_addr, cli_addr;     int n;      /*first call socket function*/     sockfd=socket(af_inet, sock_stream, 0);     setsockopt(sockfd, sol_socket, so_reuseaddr, 0, 0);     if(sockfd<0)     {         perror("error opening socket");         exit(1);     }      /*initialize socket structure*/     bzero((char*)&serv_addr, sizeof(serv_addr));     portno=5001;     serv_addr.sin_family=af_inet;     serv_addr.sin_addr.s_addr=inaddr_any;     serv_addr.sin_port=htons(portno);      /*now bind host address using bind() call.*/     if(bind(sockfd, (struct sockaddr*) &serv_addr, sizeof(serv_addr))<0)     {         perror("error on binding");         exit(1);     }      /*now start listening clients, here process     go in sleep mode , wait incoming connection*/     listen(sockfd, 5);     clilen=sizeof(cli_addr);      while(1)     {         /*accept actual connection client*/         newsockfd=accept(sockfd, (struct sockaddr*)&cli_addr, &clilen);         if(newsockfd<0)         {             perror("error on accept");             exit(1);         }            serve_request(newsockfd);     }     return 0; } 

everything works fine this. when execute ./a.out starts socket server , waits clients. when exit code using ^c stops , returns prompt.

however, if code complied last line (//close(newsockfd);) in method void serve_request(int newsockfd) uncommented , client had come , gone, on pressing ^c , invoking server again ./a.out, shows error on binding: in use.

but if have compiled code last line commented, works fine, meaning can invoke server ./a.out , have server again without waiting time in previous case.

can throw light on handling this. appreciated. thank you.

when opened socket, allocated operating system resource , told o/s taht want reuse socket address.

there no automatic cleanup when program ends. resource remains allocated.

uncomment close() , habit of freeing , resources,whether memory, sockets, mutexes or whatever.