Accept function in socket

The Problem and Solution I met I wrote a socket program last night. Because my client is a one-time program, the simplest server and client will be automatically launched once the server is connected, then run again. /client before I can connect to the server again. I found that when the first client connects to the server, the client address printed by the server is not 127.0.0.1, which is wrong! The port number is 1023. For example, I thought it was caused by the fact that the sockaddr_in struct of the user accept function in my server was not initialized. Then I added bzero (& cin, sizeof (cin )); the statement is used for the initialization of the cin struct. Then I find that the first connection is 0.0.0.0, and the port is also 0! Why? Baidu once found that a person's socket program before calling the accept function, first assign the value of len = sizeof (cliaddr) to the parameter len required by the accept function; then call acceptfc = accept (listenfd, (struct sockaddr *) & cin, & len); it was good after the test! In this way, we can see that my error lies in the incorrect accept function parameter! The accept function checks my current system (Linux 2.6.35.14-106. fc14.i686) header file in/Usr/include/Sys/socket. h defines the accept function [cpp]/* Await a connection on socket FD. when a connection arrives, open a new socket to communicate with it, set * ADDR (which is * ADDR_LEN bytes long) to the address of the connecting peer and * ADDR_LEN to theaddress's actual length, and return the new socket's descriptor, or-1 for errors. this function is Cancellation point and therefore not marked with _ THROW. */extern int accept (int _ fd, _ SOCKADDR_ARG _ addr, socklen_t * _ restrict _ addr_len ); someone found on the Internet that the last parameter of the accept function can be NULL. I tested the Code as follows: [cpp] fc = accept (fs, (struct sockaddr *) & cin, NULL); if (fc <0) {printf ("fc = % d \ n", fc); return-1 ;} when running, it is found that the running has exited, and fc =-1 is printed! It can be seen that the last parameter is not NULL! (May be caused by different system versions) my server. c [cpp] # include <stdio. h> # include <stdlib. h> # include <string. h> # include <arpa/inet. h> # define MAX_LINE 100 # define PORT 8000 void my_fun (char * p);/* convert uppercase characters to lowercase letters */void my_fun (char * p) {if (p = NULL) return; for (; * p! = '\ 0'; p ++) {if (* p> = 'A' & * p <= 'Z ') {* p = * p-'A' + 'A' ;}} int main (int argc, char ** argv) {struct sockaddr_in sin; struct sockaddr_in cin; int fs, fc; // used to create a socket. Each server and client has a socklen_t len; char buf [MAX_LINE]; char addr_p [INET_ADDRSTRLEN]; // used to save the Client ip information int n; bzero (& sin, sizeof (sin); bzero (& cin, sizeof (cin); sin. sin_family = AF_INET; sin. sin_addr.s_addr = INADDR_ANY; // The Server accepts any address sin. sin _ Port = htons (PORT); fs = socket (AF_INET, SOCK_STREAM, 0); // server socket, tcp bind (fs, (struct sockaddr *) & sin, sizeof (sin); listen (fs, 10 ); printf ("========= welcome to jack's server ===========\ n"); memset (addr_p, 0, sizeof (addr_p); while (1) {len = sizeof (cin); // len must be assigned a value; otherwise, the first client address is 0.0.0.0! Printf ("len = % d \ n", len); fc = accept (fs, (struct sockaddr *) & cin, & len ); // fc = accept (fs, (struct sockaddr *) & cin, NULL); // try not to be NULL if (fc <0) {printf ("fc = % d \ n", fc); return-1;} n = read (fc, buf, MAX_LINE ); // The read length is n inet_ntop (AF_INET, & cin. sin_addr, addr_p, sizeof (addr_p); printf ("client ip: % s, port: % d \ n", addr_p, ntohs (cin. sin_port); printf ("content: % s \ n", buf); my_fun (buf); write (fc, buf, n); close (fc );} if (close (fs) =-1) {perror ("fail to close \ n"); exit (1) ;}return 1 ;}