第四章：文件和目录

1.函数stat，fstat，lstat，fststat

  int stat(const char *restrict pathname, struct stat *restrict buf);

  int fstat(int fd, struct stat *buf);

2.文件类型:

  普通文件，目录文件，块特殊文件，字符特殊文件（系统中的设备属于这两种），FIFO，套接字，符号链接。

  代码是查看文件类型。

#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)){
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_ISSOCK(buf.st_mode))
ptr = "socket";
else if(S_ISLNK(buf.st_mode))
ptr = "symbolic link";
else
ptr = "** unknown mode **";
printf("%s\n", ptr);
}
exit(0);
}

 

3.access和faccessat(按照实际用户ID和实际组ID进行访问权限设置)

  int access(const char* pathname, int mode);

4.umask函数为进程设置文件模式创建屏蔽字

  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 foo");
umask(S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH);
if(creat("bar", RWRWRW) < 0)
err_sys("creat error bar");
exit(0);
}

5.chmod，fchmod，fchmodat;(更改文件的访问权限)
  int chmod(const char* pathname, mode_t mode);

#include "apue.h"

int main(void)
{
struct stat statbuf;
if(stat("foo", &statbuf) < 0)
err_sys("stat error foo");

if(chmod("foo", (statbuf.st_mode & ~S_IXGRP) | S_ISGID) < 0)
err_sys("chmod error foo");

if(chmod("bar", S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH) < 0)
err_sys("chmod error bar");
exit(0);
}

6.chown，fchown，fchownat，lchown(更改文件的用户ID和组ID)
  int chown(const char* pathname, uid_t owner, gid_t group);

7.文件截断。(truncate和ftruncate函数)

  int truncate(const char* pathname, off_t length); 

  将文件长度截断为length，如果长度大于length，则超过的部分就不能被访问；如果长度小于length，则会形成空洞。

8.link，linkat，unlink，unlinkat，remove

  创建一个现有文件的链接

  int link(const char* existingpath, const char* newpath);

  删除一个现有的目录项

  int unlink(const char* pathname);

9.rename和renameat函数

  对文件或者目录进行重命名操作。

  int rename(const char* oldname, const char* newname);

10.创建和读取符号链接

  int symlink(const char* actualpath, const char* sympath); //创建了一个指向actualpath的新目录项sympath。

  打开符号链接

  ssize_t readlink(const char* restrict pathname, char* restrict buf, size_t bufsize);

11.文件时间

  ls命令按这3个时间值中的一个排序进行显示。系统默认（-l或-t）是按文件的修改时间的先后排序显示，-u是按访问时间排序，-c是按状态更改时间排序。st_atim最后访问时间，st_mtim最后修改时间，st_ctim表示i节点状态最后更改时间。

12.futimens，utimensat，utimes函数。

  用于一个文件的访问和修改时间的更改。

#include "apue.h"
#include <fcntl.h>

int main(int argc, char* argv[])
{
int i, fd;
struct stat statbuf;
struct timespec times[2];

for(i = 1; i < argc; i ++){
if(stat(argv[i], &statbuf) < 0){
err_ret("%s: stat error", argv[i]);
continue;
}
if((fd = open(argv[i], O_RDWR | O_TRUNC)) < 0){
err_ret("%s: open error", argv[i]);
continue;
}
times[0] = statbuf.st_atim;
times[1] = statbuf.st_mtim;
if(futimens(fd, times) < 0)
err_ret("%s: futimens error", argv[i]);
close(fd);
}
exit(0);
}

13.目录创建和删除(mkdir，mkdirat，rmdir)
  int mkdir(const char* pathname, mode_t mode);

14.读目录

  DIR *opendir(const char* pathname);

  DIR *fdopendir(int fd);

  struct dirent *readdir(DIR *dp);

  void rewinddir(DIR *dp);

  int closedir(DIR *dp);

  long telldir(DIR *dp);

  void seekdir(DIR *dp, long loc);

#include "apue.h"
#include <dirent.h>
#include <limits.h>

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);
ntot = nreg + ndir + nblk + nchr + nfifo + nslink + nsock;
if(ntot == 0)
ntot = 1;
printf("regular files = %ld\n", nreg);
printf("directories = %ld\n", ndir);
printf("block special = %ld\n", nblk);
printf("char special = %ld\n", nchr);
printf("FIFOs = %ld\n", nfifo);
printf("symbolic links =%ld\n", nslink);
printf("sockets =%ld\n", nsock);
exit(ret);
}

#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;  /* contain full pathname for every file */
static size_t pathlen;

static int myftw(char *pathname, Myfunc *func)
{
fullpath = path_alloc(&pathlen);

if(pathlen <= strlen(pathname)){
pathlen = strlen(pathname) * 2;
if((fullpath = realloc(fullpath, pathlen)) == NULL)
err_sys("realloc failed");
}
strcpy(fullpath, pathname);
return (dopath(func));
}

static int dopath(Myfunc *func)
{
struct stat statbuf;
struct dirent *dirp;
DIR *dp;
int ret, n;

if(lstat(fullpath, &statbuf) < 0)
return (func(fullpath, &statbuf, FTW_NS));
if(S_ISDIR(statbuf.st_mode) == 0) /* not a directory */
return (func(fullpath, &statbuf, FTW_F));
if((ret = func(fullpath, &statbuf, FTW_D)) != 0)
return ret;
n = strlen(fullpath);
if(n + NAME_MAX + 2 > pathlen){
pathlen *= 2;
if((fullpath = realloc(fullpath, pathlen)) == NULL)
err_sys("realloc failed");
}
fullpath[n ++] = '/';
fullpath
= 0;
if((dp = opendir(fullpath)) == NULL)
return (func(fullpath, &statbuf, FTW_DNR));
while((dirp = readdir(dp)) != NULL){
if((ret = dopath(func)) != 0)
break;
}
fullpath[n - 1] = 0;
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);
}
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;
}

15.更改当前工作目录。

  chdir，fchdir，getcd。

  int chdir(const char* pathname);

  int fchdir(int fd);

  char* getcwd(char* buf, size_t size);