UDPdaytime程序

/* connectsock.c - connectsock */ #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <netdb.h> #include <string.h> #include <stdlib.h> #include <errno.h> #ifndef INADDR_NONE #define INADDR_NONE 0xffffffff #endif /* INADDR_NONE */ extern int errno; int errexit(const char *format, ...); /*------------------------------------------------------------------------ * connectsock - allocate & connect a socket using TCP or UDP *------------------------------------------------------------------------ */ int connectsock(const char *host, const char *service, const char *transport ) /* * Arguments: * host - name of host to which connection is desired * service - service associated with the desired port * transport - name of transport protocol to use ("tcp" or "udp") */ { struct hostent *phe; /* pointer to host information entry */ struct servent *pse; /* pointer to service information entry */ struct protoent *ppe; /* pointer to protocol information entry*/ struct sockaddr_in sin; /* an Internet endpoint address */ int s, type; /* socket descriptor and socket type */ memset(&sin, 0, sizeof(sin)); sin.sin_family = AF_INET; /* Map service name to port number */ if ( pse = getservbyname(service, transport) ) sin.sin_port = pse->s_port; else if ((sin.sin_port=htons((unsigned short)atoi(service))) == 0) errexit("can't get \"%s\" service entry\n", service); /* Map host name to IP address, allowing for dotted decimal */ if ( phe = gethostbyname(host) ) memcpy(&sin.sin_addr, phe->h_addr, phe->h_length); else if ( (sin.sin_addr.s_addr = inet_addr(host)) == INADDR_NONE ) errexit("can't get \"%s\" host entry\n", host); /* Map transport protocol name to protocol number */ if ( (ppe = getprotobyname(transport)) == 0) errexit("can't get \"%s\" protocol entry\n", transport); /* Use protocol to choose a socket type */ if (strcmp(transport, "udp") == 0) type = SOCK_DGRAM; else type = SOCK_STREAM; /* Allocate a socket */ s = socket(PF_INET, type, ppe->p_proto); if (s < 0) errexit("can't create socket: %s\n", strerror(errno)); /* Connect the socket */ if (connect(s, (struct sockaddr *)&sin, sizeof(sin)) < 0) errexit("can't connect to %s.%s: %s\n", host, service, strerror(errno)); return s; }