unix/linux編程實踐教程：服務器與socket

1. popen：讓進程看似文件

#include <stdio.h>
#include <stdlib.h>

int main( void )
{
        FILE    *fp;
        char    buf[ 100 ];
        int     i = 0;

        fp = popen("who|sort","r");

        while ( fgets(buf, 100, fp) != NULL )
                printf("%3d %s", i++, buf );

        pclose( fp );

        return 0;
}

    程序輸出：

leichaojian@ThinkPad-T430i:~$ cc popendemo.c
leichaojian@ThinkPad-T430i:~$ ./a.out
  0 leichaojian :0           2014-09-02 22:38 (:0)
  1 leichaojian pts/0        2014-09-02 23:01 (:0)

2. 一個簡單的socket例子：時間服務器

服務器timeserv.c:

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <time.h>
#include <strings.h>

#define PORTNUM 13000
#define HOSTLEN 256
#define oops(msg) {perror(msg);exit(1);}

int main( int ac, char *av[] )
{
	struct sockaddr_in saddr;
	struct hostent *hp;
	char	hostname[ HOSTLEN ];
	int	sock_id, sock_fd;
	FILE	*sock_fp;
	char	*ctime();
	time_t	thetime;

	sock_id = socket( PF_INET, SOCK_STREAM, 0 );
	if ( sock_id == -1 )
		oops("socket");
	bzero((void *)&saddr, sizeof(saddr));
	gethostname(hostname, HOSTLEN);
	hp = gethostbyname(hostname);

	bcopy((void *)hp->h_addr, ( void *)&saddr.sin_addr, hp->h_length);
	saddr.sin_port = htons(PORTNUM);
	saddr.sin_family = AF_INET;

	if ( bind(sock_id, (struct sockaddr *)&saddr, sizeof( saddr )) != 0 )
		oops("bind");

	if ( listen( sock_id, 1) != 0 )
		oops("listen");

	while ( 1 ){
		sock_fd = accept( sock_id, NULL, NULL );
		printf("wow!got a call!\n");
		if ( sock_fd == -1 )
			oops("accept");
		sock_fp = fdopen(sock_fd, "w");
		if ( sock_fp == NULL )
			oops("fdopen");
		thetime = time( NULL );
		fprintf(sock_fp, "the time here is..");
		fprintf( sock_fp, "%s", ctime(&thetime));
		fclose( sock_fp );
	}

	return 0;
}

而客戶端的代碼如下：

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>

#define oops(msg) {perror(msg);exit(1);}

int main( int ac, char *av[] )
{
	struct sockaddr_in servadd;
	struct hostent *hp;
	int	sock_id, sock_fd;
	char	message[ BUFSIZ ];
	int	messlen;

	sock_id = socket( AF_INET, SOCK_STREAM, 0);
	if ( sock_id == -1 )
		oops("socket");

	bzero(&servadd, sizeof(servadd));

	hp = gethostbyname(av[1]);
	if ( hp == NULL)
		oops(av[1]);
	bcopy(hp->h_addr, (struct sockaddr*)&servadd.sin_addr, hp->h_length);
	servadd.sin_port = htons(atoi(av[2]));
	servadd.sin_family = AF_INET;

	if(connect(sock_id, (struct sockaddr *)&servadd, sizeof(servadd)) != 0)
		oops("connect");

	messlen = read(sock_id, message, BUFSIZ);
	if (messlen == -1 )
		oops("read");
	if ( write(1, message, messlen ) != messlen )
		oops("write");
	close( sock_id );

	return 0;
}

服務端運行如下：

leichaojian@ThinkPad-T430i:~$ ./a.out&
[3] 12397

客戶端爲：

leichaojian@ThinkPad-T430i:~$ ./a.out ThinkPad-T430i 13000
the time here is..Wed Sep  3 00:00:15 2014
leichaojian@ThinkPad-T430i:~$ hostname
ThinkPad-T430i