AUPE学习第一章------UNIX基础知识

1.3.3路径名

运行myls.c可以显示出参数给出的目录，需要手动导入ourhdr.h,ourhdr.c,error.c这三个文件。下面为这几个文件的内容：

myls.c如下：

#include <sys/types.h>
#include <dirent.h>
#include "ourhdr.h"
#include "error.c"
int main(int argc,char *argv[])
{
    DIR *dp; 
    struct dirent *dirp;
    if (argc != 2)
       err_quit("a single argument is required");
    if ((dp = opendir(argv[1])) == NULL)
       err_sys("can't open %s",argv[1]);
    while ((dirp = readdir(dp)) != NULL)
       printf("%s\n",dirp->d_name);
    closedir(dp);
    exit(0);
}

opendir()返回指向DIR结构的指针，并将该指针传向readdir()函数。在循环中调用readdir()来读取每个目录项，它返回一个指向dirent结构的指针。

ourhdr.h如下：

/* Our own header, to be included *after* all standard system headers */

#ifndef	__ourhdr_h
#define	__ourhdr_h

#include	<sys/types.h>	/* required for some of our prototypes */
#include	<stdio.h>		/* for convenience */
#include	<stdlib.h>		/* for convenience */
#include	<string.h>		/* for convenience */
#include	<unistd.h>		/* for convenience */

#define	MAXLINE	4096			/* max line length */

#define	FILE_MODE	(S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)
					/* default file access permissions for new files */
#define	DIR_MODE	(FILE_MODE | S_IXUSR | S_IXGRP | S_IXOTH)
					/* default permissions for new directories */

typedef	void	Sigfunc(int);	/* for signal handlers */

					/* 4.3BSD Reno <signal.h> doesn't define SIG_ERR */
#if	defined(SIG_IGN) && !defined(SIG_ERR)
#define	SIG_ERR	((Sigfunc *)-1)
#endif

#define	min(a,b)	((a) < (b) ? (a) : (b))
#define	max(a,b)	((a) > (b) ? (a) : (b))

					/* prototypes for our own functions */
char	*path_alloc(int *);			/* {Prog pathalloc} */
int		 open_max(void);			/* {Prog openmax} */
void	 clr_fl(int, int);			/* {Prog setfl} */
void	 set_fl(int, int);			/* {Prog setfl} */
void	 pr_exit(int);				/* {Prog prexit} */
void	 pr_mask(const char *);		/* {Prog prmask} */
Sigfunc	*signal_intr(int, Sigfunc *);/* {Prog signal_intr_function} */

int		 tty_cbreak(int);			/* {Prog raw} */
int		 tty_raw(int);				/* {Prog raw} */
int		 tty_reset(int);			/* {Prog raw} */
void	 tty_atexit(void);			/* {Prog raw} */
#ifdef	ECHO	/* only if <termios.h> has been included */
struct termios	*tty_termios(void);	/* {Prog raw} */
#endif

void	 sleep_us(unsigned int);	/* {Ex sleepus} */
ssize_t	 readn(int, void *, size_t);/* {Prog readn} */
ssize_t	 writen(int, const void *, size_t);/* {Prog writen} */
int		 daemon_init(void);			/* {Prog daemoninit} */

int		 s_pipe(int *);				/* {Progs svr4_spipe bsd_spipe} */
int		 recv_fd(int, ssize_t (*func)(int, const void *, size_t));
									/* {Progs recvfd_svr4 recvfd_43bsd} */
int		 send_fd(int, int);			/* {Progs sendfd_svr4 sendfd_43bsd} */
int		 send_err(int, int, const char *);/* {Prog senderr} */
int		 serv_listen(const char *);	/* {Progs servlisten_svr4 servlisten_44bsd} */
int		 serv_accept(int, uid_t *);	/* {Progs servaccept_svr4 servaccept_44bsd} */
int		 cli_conn(const char *);	/* {Progs cliconn_svr4 cliconn_44bsd} */
int		 buf_args(char *, int (*func)(int, char **));
									/* {Prog bufargs} */

int		 ptym_open(char *);			/* {Progs ptyopen_svr4 ptyopen_44bsd} */
int		 ptys_open(int, char *);	/* {Progs ptyopen_svr4 ptyopen_44bsd} */
#ifdef	TIOCGWINSZ
pid_t	 pty_fork(int *, char *, const struct termios *,
				  const struct winsize *);	/* {Prog ptyfork} */
#endif

int		lock_reg(int, int, int, off_t, int, off_t);
									/* {Prog lockreg} */
#define	read_lock(fd, offset, whence, len) \
			lock_reg(fd, F_SETLK, F_RDLCK, offset, whence, len)
#define	readw_lock(fd, offset, whence, len) \
			lock_reg(fd, F_SETLKW, F_RDLCK, offset, whence, len)
#define	write_lock(fd, offset, whence, len) \
			lock_reg(fd, F_SETLK, F_WRLCK, offset, whence, len)
#define	writew_lock(fd, offset, whence, len) \
			lock_reg(fd, F_SETLKW, F_WRLCK, offset, whence, len)
#define	un_lock(fd, offset, whence, len) \
			lock_reg(fd, F_SETLK, F_UNLCK, offset, whence, len)

pid_t	lock_test(int, int, off_t, int, off_t);
									/* {Prog locktest} */

#define	is_readlock(fd, offset, whence, len) \
			lock_test(fd, F_RDLCK, offset, whence, len)
#define	is_writelock(fd, offset, whence, len) \
			lock_test(fd, F_WRLCK, offset, whence, len)

void	err_dump(const char *, ...);	/* {App misc_source} */
void	err_msg(const char *, ...);
void	err_quit(const char *, ...);
void	err_ret(const char *, ...);
void	err_sys(const char *, ...);

void	log_msg(const char *, ...);		/* {App misc_source} */
void	log_open(const char *, int, int);
void	log_quit(const char *, ...);
void	log_ret(const char *, ...);
void	log_sys(const char *, ...);

void	TELL_WAIT(void);		/* parent/child from {Sec race_conditions} */
void	TELL_PARENT(pid_t);
void	TELL_CHILD(pid_t);
void	WAIT_PARENT(void);
void	WAIT_CHILD(void);

#endif	/* __ourhdr_h */

ourhdr.c如下：

#include "apue.h"
#include <errno.h>		/* for definition of errno */
#include <stdarg.h>		/* ISO C variable aruments */

static void	err_doit(int, int, const char *, va_list);

/*
 * Nonfatal error related to a system call.
 * Print a message and return.
 */
void
err_ret(const char *fmt, ...)
{
	va_list		ap;

	va_start(ap, fmt);
	err_doit(1, errno, fmt, ap);
	va_end(ap);
}

/*
 * Fatal error related to a system call.
 * Print a message and terminate.
 */
void
err_sys(const char *fmt, ...)
{
	va_list		ap;

	va_start(ap, fmt);
	err_doit(1, errno, fmt, ap);
	va_end(ap);
	exit(1);
}

/*
 * Fatal error unrelated to a system call.
 * Error code passed as explict parameter.
 * Print a message and terminate.
 */
void
err_exit(int error, const char *fmt, ...)
{
	va_list		ap;

	va_start(ap, fmt);
	err_doit(1, error, fmt, ap);
	va_end(ap);
	exit(1);
}

/*
 * Fatal error related to a system call.
 * Print a message, dump core, and terminate.
 */
void
err_dump(const char *fmt, ...)
{
	va_list		ap;

	va_start(ap, fmt);
	err_doit(1, errno, fmt, ap);
	va_end(ap);
	abort();		/* dump core and terminate */
	exit(1);		/* shouldn't get here */
}

/*
 * Nonfatal error unrelated to a system call.
 * Print a message and return.
 */
void
err_msg(const char *fmt, ...)
{
	va_list		ap;

	va_start(ap, fmt);
	err_doit(0, 0, fmt, ap);
	va_end(ap);
}

/*
 * Fatal error unrelated to a system call.
 * Print a message and terminate.
 */
void
err_quit(const char *fmt, ...)
{
	va_list		ap;

	va_start(ap, fmt);
	err_doit(0, 0, fmt, ap);
	va_end(ap);
	exit(1);
}

/*
 * Print a message and return to caller.
 * Caller specifies "errnoflag".
 */
static void
err_doit(int errnoflag, int error, const char *fmt, va_list ap)
{
	char	buf[MAXLINE];

	vsnprintf(buf, MAXLINE, fmt, ap);
	if (errnoflag)
		snprintf(buf+strlen(buf), MAXLINE-strlen(buf), ": %s",
		  strerror(error));
	strcat(buf, "\n");
	fflush(stdout);		/* in case stdout and stderr are the same */
	fputs(buf, stderr);
	fflush(NULL);		/* flushes all stdio output streams */
}

error.c如下：

#include	<errno.h>		/* for definition of errno */
#include	<stdarg.h>		/* ANSI C header file */
#include	"ourhdr.h"

static void	err_doit(int, const char *, va_list);

char	*pname = NULL;		/* caller can set this from argv[0] */

/* Nonfatal error related to a system call.
 * Print a message and return. */

void
err_ret(const char *fmt, ...)
{
	va_list		ap;

	va_start(ap, fmt);
	err_doit(1, fmt, ap);
	va_end(ap);
	return;
}

/* Fatal error related to a system call.
 * Print a message and terminate. */

void
err_sys(const char *fmt, ...)
{
	va_list		ap;

	va_start(ap, fmt);
	err_doit(1, fmt, ap);
	va_end(ap);
	exit(1);
}

/* Fatal error related to a system call.
 * Print a message, dump core, and terminate. */

void
err_dump(const char *fmt, ...)
{
	va_list		ap;

	va_start(ap, fmt);
	err_doit(1, fmt, ap);
	va_end(ap);
	abort();		/* dump core and terminate */
	exit(1);		/* shouldn't get here */
}

/* Nonfatal error unrelated to a system call.
 * Print a message and return. */

void
err_msg(const char *fmt, ...)
{
	va_list		ap;

	va_start(ap, fmt);
	err_doit(0, fmt, ap);
	va_end(ap);
	return;
}

/* Fatal error unrelated to a system call.
 * Print a message and terminate. */

void
err_quit(const char *fmt, ...)
{
	va_list		ap;

	va_start(ap, fmt);
	err_doit(0, fmt, ap);
	va_end(ap);
	exit(1);
}

/* Print a message and return to caller.
 * Caller specifies "errnoflag". */

static void
err_doit(int errnoflag, const char *fmt, va_list ap)
{
	int		errno_save;
	char	buf[MAXLINE];

	errno_save = errno;		/* value caller might want printed */
	vsprintf(buf, fmt, ap);
	if (errnoflag)
		sprintf(buf+strlen(buf), ": %s", strerror(errno_save));
	strcat(buf, "\n");
	fflush(stdout);		/* in case stdout and stderr are the same */
	fputs(buf, stderr);
	fflush(NULL);		/* flushes all stdio output streams */
	return;
}

求根目录下的所有目录和文件。

运行结果如下：

[root@localhost apue]# gcc myls.c 
[root@localhost apue]# ls
a.out  error.c  error.c~  myls.c  ourhdr.c  ourhdr.h
[root@localhost apue]# a.out /
home
usr
.
dev
srv
opt
.autofsck
lib
misc
boot

文件描述符是一个小的非负整数，内核通过文件描述符来打开一个文件。

函数open(),read(),write(),lseek(),close()提供了不用缓存的I/O。这些函数都是通过文件描述符进行工作。

1.4.3不用缓存的I/O

如果愿意从标准输入读，并写向标准输出，下面程序用于复制任意UNIX文件

iotest.c如下：

[root@localhost apue]# cat iotest.c
#include "ourhdr.h"
#include "error.c"
#define BUFFSIZE 8192

int main(void)
{
    int n;
    char buf[BUFFSIZE];
    while ((n = read(STDIN_FILENO, buf, BUFFSIZE)) > 0)
        if (write(STDOUT_FILENO, buf, n) != n)
            err_sys("write error");
    if (n < 0)
        err_sys("read error");
    exit(0);
}

两个常数STDIN_FILENO和STDOUT_FILENO定义在头文件<unistd.h>中，read()和write()函数都在这个文件中定义。他们指定了标准输入和输出的文件描述符。

read()函数返回读得的字节数，此值用作要写的字节数当达到文件尾端时，read（）返回0，程序停止执行，如果遇到错误，read返回-1。

运行结果如下：

[root@localhost apue]# gcc -o iotest.out iotest.c 
[root@localhost apue]# ls
a.out  error.c   iotest.c    myls.c    ourhdr.h
data   error.c~  iotest.out  ourhdr.c
[root@localhost apue]# iotest.out > data
-bash: iotest.out: command not found
[root@localhost apue]# ./iotest.out > data
nihao huangchengdu
hahahaah
[root@localhost apue]# cat data
nihao huangchengdu
hahahaah

1.4.4标准I/O

标准I/O函数提供一种不用缓存的I/O函数的提供一种带缓存的方式。fgets函数读取完整的一行，read函数读取指定的字节数。

我们最熟悉的标准I/O函数是printf函数，它是存在头文件<stdio.h>中，这个头文件包含所有标准I/O的函数原型。