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UNIX编程(4)-文件和目录
1.stat,fstat,lstat函数
#include <sys/stat.h>
int stat(const char *restrict pathname, struct
stat *restrict buf);
int fstat(int filedes, struct stat *buf);
int lstat(const char *restrict pathname, struct
stat *restrict buf);
当命名文件是一个符号链接时，lstat返回该符号链接的有关信息，而不是由该符号链接引用文件的信息。
stat 结构体说明
struct stat {
mode_t st_mode; /* file type & mode (permissions) */
ino_t st_ino; /* i-node number (serial number) */
dev_t st_dev; /* device number (file system) */
dev_t st_rdev; /* device number for special files */
nlink_t st_nlink; /* number of links */
uid_t st_uid; /* user ID of owner */
gid_t st_gid; /* group ID of owner */
off_t st_size; /* size in bytes, for regular files */
time_t st_atime; /* time of last access */
time_t st_mtime; /* time of last modification */
time_t st_ctime; /* time of last file status change */
blksize_t st_blksize; /* best I/O block size */
blkcnt_t st_blocks; /* number of disk blocks allocated */
};
2.文件类型
文件类型包括：
普通文件
目录文件
块特殊文件
字符特殊文件
FIFO
套接字
符号链接
例：
打印文件类型
#include "apue.h"
int
main(int argc, char *argv[])
{
int i;
struct stat buf;
char *ptr;
for (i = 1; i < argc; i++) {
printf("%s: ", argv[i]);
if (lstat(argv[i], &buf) < 0) {
err_ret("lstat error");
continue;
}
if (S_ISREG(buf.st_mode))
ptr = "regular";
else if (S_ISDIR(buf.st_mode))
ptr = "directory";
else if (S_ISCHR(buf.st_mode))
ptr = "character special";
else if (S_ISBLK(buf.st_mode))
ptr = "block special";
else if (S_ISFIFO(buf.st_mode))
ptr = "fifo";
else if (S_ISLNK(buf.st_mode))
ptr = "symbolic link";
else if (S_ISSOCK(buf.st_mode))
ptr = "socket";
else
ptr = "** unknown mode **";
printf("%sn", ptr);
}
exit(0);
}
3.用户ID和设置组ID
与一个进程相关联的ID有6个或更多：
实际用户ID
实际组ID
有效用户ID
有效组ID
附件组ID
保存的设置用户组ID
保存的设置组ID
4.文件访问权限
st_mode包含了针对文件的访问权限位，每个文件有9个访问权限位，如下：
S_IRUSR 用户读
S_IWUSR 用户写
S_IXUSR 用户执行
S_IRGRP 组读
S_IWGRP 组写
S_IXGRP 组执行
S_IROTH 其他读
S_IWOTH 其他写
S_IXOTH 其他执行
5.access函数
access函数按实际用户ID和实际组ID进行访问权限测试
#include <unistd.h>
int access(const char *pathname, int mode);
#include "apue.h"
#include <fcntl.h>
int
main(int argc, char *argv[])
{
if (argc != 2)
err_quit("usage: a.out <pathname>");
if (access(argv[1], R_OK) < 0)
err_ret("access error for %s", argv[1]);
else
printf("read access OKn");
if (open(argv[1], O_RDONLY) < 0)
err_ret("open error for %s", argv[1]);
else
printf("open for reading OKn");
exit(0);
}
6.umask函数
umask函数为进程设置文件模式创建屏蔽字，并返回以前的值
#include <sys/stat.h>
mode_t umask(mode_t cmask);
#include "apue.h"
#include <fcntl.h>
#define RWRWRW (S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP|S_IROTH|S_IWOTH)
int
main(void)
{
umask(0);
if (creat("foo", RWRWRW) < 0)
err_sys("creat error for foo");
umask(S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH);
if (creat("bar", RWRWRW) < 0)
err_sys("creat error for bar");
exit(0);
}
7.chmod和fchmod函数
修改文件的权限位。进程的有效用户ID必须等于文件所有者ID，或者该进程必须具有超级用户权限
#include <sys/stat.h>
int chmod(const char *pathname, mode_t mode);
int fchmod(int filedes, mode_t mode);
#include "apue.h"
int
main(void)
{
struct stat statbuf;
/* turn on set-group-ID and turn off group-execute */
if (stat("foo", &statbuf) < 0)
err_sys("stat error for foo");
if (chmod("foo", (statbuf.st_mode & ~S_IXGRP) | S_ISGID) < 0)
err_sys("chmod error for foo");
/* set absolute mode to "rw-r--r--" */
if (chmod("bar", S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH) < 0)
err_sys("chmod error for bar");
exit(0);
}
8.粘住位
S_ISVTX称为粘住位，对一个目录设置了粘住位以后，则只有对该目录具有写权限的用户在满足下列条件之一的情况下，才能删除或更名该目录下的文件：
拥有此文件
拥有此目录
是超级用户
9.chown,fchown和lchown函数
更改文件用户所有者ID 或组ID
#include <unistd.h>
int chown(const char *pathname, uid_t owner, gid_t
group);
int fchown(int filedes, uid_t owner, gid_t group);
int lchown(const char *pathname, uid_t owner,
gid_t group);
10.文件截短
将现有的文件长度截短为length字节
#include <unistd.h>
int truncate(const char *pathname, off_t length);
int ftruncate(int filedes, off_t length);
11.link,unlink,remove和rename函数
#include <unistd.h>
int link(const char *existingpath, const char
*newpath);
#include <unistd.h>
int unlink(const char *pathname);
#include "apue.h"
#include <fcntl.h>
int
main(void)
{
if (open("tempfile", O_RDWR) < 0)
err_sys("open error");
if (unlink("tempfile") < 0)
err_sys("unlink error");
printf("file unlinkedn");
sleep(15);
printf("donen");
exit(0);
}
#include <stdio.h>
int remove(const char *pathname);
重命名文件
#include <stdio.h>
int rename(const char *oldname, const char *newname);
12.symlink和readlink函数
symlink创建一个符号链接
#include <unistd.h>
int symlink(const char *actualpath, const char
*sympath);
readlink 打开符号链接文件本身
#include <unistd.h>
ssize_t readlink(const char* restrict pathname,
char *restrict buf,
size_t bufsize);
13.utime函数
#include <utime.h>
int utime(const char *pathname, const struct
utimbuf *times);
函数使用的结构体为：
struct utimbuf {
time_t actime; /* access time */
time_t modtime; /* modification time */
}
#include "apue.h"
#include <fcntl.h>
#include <utime.h>
int
main(int argc, char *argv[])
{
int i, fd;
struct stat statbuf;
struct utimbuf timebuf;
for (i = 1; i < argc; i++) {
if (stat(argv[i], &statbuf) < 0) { /* fetch current times */
err_ret("%s: stat error", argv[i]);
continue;
}
if ((fd = open(argv[i], O_RDWR | O_TRUNC)) < 0) { /* truncate */
err_ret("%s: open error", argv[i]);
continue;
}
close(fd);
timebuf.actime = statbuf.st_atime;
timebuf.modtime = statbuf.st_mtime;
if (utime(argv[i], &timebuf) < 0) { /* reset times */
err_ret("%s: utime error", argv[i]);
continue;
}
}
exit(0);
}
14.mkdir和rmdir函数
mkdir函数创建目录,rmdir删除目录
#include <sys/stat.h>
int mkdir(const char *pathname, mode_t mode);
#include <unistd.h>
int rmdir(const char *pathname);
15.读目录
#include <dirent.h>
DIR *opendir(const char *pathname);
Returns: pointer if OK, NULL on error
struct dirent *readdir(DIR *dp);
Returns: pointer if OK, NULL at end of directory or error
void rewinddir(DIR *dp);
int closedir(DIR *dp);
Returns: 0 if OK, 1 on error
long telldir(DIR *dp);
Returns: current location in directory associated with dp
void seekdir(DIR *dp, long loc);
递归遍历目录结构并按文件类型计数
#include "apue.h"
#include <dirent.h>
#include <limits.h>
/* function type that is called for each filename */
typedef int Myfunc(const char *, const struct stat *, int);
static Myfunc myfunc;
static int myftw(char *, Myfunc *);
static int dopath(Myfunc *);
static long nreg, ndir, nblk, nchr, nfifo, nslink, nsock, ntot;
int
main(int argc, char *argv[])
{
int ret;
if (argc != 2)
err_quit("usage: ftw <starting-pathname>");
ret = myftw(argv[1], myfunc); /* does it all */
ntot = nreg + ndir + nblk + nchr + nfifo + nslink + nsock;
if (ntot == 0)
ntot = 1; /* avoid divide by 0; print 0 for all counts */
printf("regular files = %7ld, %5.2f %%n", nreg,
nreg*100.0/ntot);
printf("directories = %7ld, %5.2f %%n", ndir,
ndir*100.0/ntot);
printf("block special = %7ld, %5.2f %%n", nblk,
nblk*100.0/ntot);
printf("char special = %7ld, %5.2f %%n", nchr,
nchr*100.0/ntot);
printf("FIFOs = %7ld, %5.2f %%n", nfifo,
nfifo*100.0/ntot);
printf("symbolic links = %7ld, %5.2f %%n", nslink,
nslink*100.0/ntot);
printf("sockets = %7ld, %5.2f %%n", nsock,
nsock*100.0/ntot);
exit(ret);
}
/*
* Descend through the hierarchy, starting at "pathname".
* The caller's func() is called for every file.
*/
#define FTW_F 1 /* file other than directory */
#define FTW_D 2 /* directory */
#define FTW_DNR 3 /* directory that can't be read */
#define FTW_NS 4 /* file that we can't stat */
static char *fullpath; /* contains full pathname for every file */
static int /* we return whatever func() returns */
myftw(char *pathname, Myfunc *func)
{
int len;
fullpath = path_alloc(&len); /* malloc's for PATH_MAX+1 bytes */
/* (Figure 2.15) */
strncpy(fullpath, pathname, len); /* protect against */
fullpath[len-1] = 0; /* buffer overrun */
return(dopath(func));
}
/*
* Descend through the hierarchy, starting at "fullpath".
* If "fullpath" is anything other than a directory, we lstat() it,
* call func(), and return. For a directory, we call ourself
* recursively for each name in the directory.
*/
static int /* we return whatever func() returns */
dopath(Myfunc* func)
{
struct stat statbuf;
struct dirent *dirp;
DIR *dp;
int ret;
char *ptr;
if (lstat(fullpath, &statbuf) < 0) /* stat error */
return(func(fullpath, &statbuf, FTW_NS));
if (S_ISDIR(statbuf.st_mode) == 0) /* not a directory */
return(func(fullpath, &statbuf, FTW_F));
/*
* It's a directory. First call func() for the directory,
* then process each filename in the directory.
*/
if ((ret = func(fullpath, &statbuf, FTW_D)) != 0)
return(ret);
ptr = fullpath + strlen(fullpath); /* point to end of fullpath */
*ptr++ = '/';
*ptr = 0;
if ((dp = opendir(fullpath)) == NULL) /* can't read directory */
return(func(fullpath, &statbuf, FTW_DNR));
while ((dirp = readdir(dp)) != NULL) {
if (strcmp(dirp->d_name, ".") == 0 ||
strcmp(dirp->d_name, "..") == 0)
continue; /* ignore dot and dot-dot */
strcpy(ptr, dirp->d_name); /* append name after slash */
if ((ret = dopath(func)) != 0) /* recursive */
break; /* time to leave */
}
ptr[-1] = 0; /* erase everything from slash onwards */
if (closedir(dp) < 0)
err_ret("can't close directory %s", fullpath);
return(ret);
}
static int
myfunc(const char *pathname, const struct stat *statptr, int type)
{
switch (type) {
case FTW_F:
switch (statptr->st_mode & S_IFMT) {
case S_IFREG: nreg++; break;
case S_IFBLK: nblk++; break;
case S_IFCHR: nchr++; break;
case S_IFIFO: nfifo++; break;
case S_IFLNK: nslink++; break;
case S_IFSOCK: nsock++; break;
case S_IFDIR:
err_dump("for S_IFDIR for %s", pathname);
/* directories should have type = FTW_D */
}
break;
case FTW_D:
ndir++;
break;
case FTW_DNR:
err_ret("can't read directory %s", pathname);
break;
case FTW_NS:
err_ret("stat error for %s", pathname);
break;
default:
err_dump("unknown type %d for pathname %s", type, pathname);
}
return(0);
}
16.chdir,fchdir和getcwd函数
chdir和fchdir 改变当前工作目录
#include <unistd.h>
int chdir(const char *pathname);
int fchdir(int filedes);
#include "apue.h"
int
main(void)
{
if (chdir("/tmp") < 0)
err_sys("chdir failed");
printf("chdir to /tmp succeededn");
exit(0);
}
getcwd获得当前的全路径
#include <unistd.h>
char *getcwd(char *buf, size_t size);
#include "apue.h"
int
main(void)
{
char *ptr;
int size;
if (chdir("/usr/spool/uucppublic") < 0)
err_sys("chdir failed");
ptr = path_alloc(&size); /* our own function */
if (getcwd(ptr, size) == NULL)
err_sys("getcwd failed");
printf("cwd = %sn", ptr);
exit(0);
}
17.设备特殊文件
设备号所用的存储类型是dev_t,通常用major和minor这两个宏来访问主次设备号。
系统中于每个文件名关联的st_dev值是文件系统的设备号，只有字符特殊文件和块特殊文件才有st_rdev值.
例：打印st_dev和st_rdev值
#include "apue.h"
#ifdef SOLARIS
#include <sys/mkdev.h>
#endif
int
main(int argc, char *argv[])
{
int i;
struct stat buf;
for (i = 1; i < argc; i++) {
printf("%s: ", argv[i]);
if (stat(argv[i], &buf) < 0) {
err_ret("stat error");
continue;
}
printf("dev = %d/%d", major(buf.st_dev), minor(buf.st_dev));
if (S_ISCHR(buf.st_mode) || S_ISBLK(buf.st_mode)) {
printf(" (%s) rdev = %d/%d",
(S_ISCHR(buf.st_mode)) ? "character" : "block",
major(buf.st_rdev), minor(buf.st_rdev));
}
printf("n");
}
exit(0);
}