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。