對某個(gè)目錄具有訪問權(quán)限的任一用戶都可讀該目錄，但是，為了防止文件系統(tǒng)產(chǎn)生混亂，只有內(nèi)核才能寫目錄。一個(gè)目錄的寫權(quán)限位和執(zhí)行權(quán)限位決定了在該目錄中能否創(chuàng)建新文件以及刪除文件，它們并不表示能否寫目錄本身。

#include <dirent.h>DIR *opendir( const char *pathname );返回值：若成功則返回指針，若出錯(cuò)則返回NULLstruct dirent *readdir( DIR *dp );返回值：若成功則返回指針，若在目錄結(jié)尾或出錯(cuò)則返回NULLvoid rewinddir( DIR *dp );int closedir( DIR *dp );返回值：若成功則返回0，若出錯(cuò)則返回-1long telldir( DIR *dp );返回值：與dp關(guān)聯(lián)的目錄中的當(dāng)前位置void seekdir( DIR *dp, long loc );

頭文件<dirent.h>中定義的dirent結(jié)構(gòu)與實(shí)現(xiàn)有關(guān)。幾種典型的UNIX實(shí)現(xiàn)對此結(jié)構(gòu)所作的定義至少包含下列兩個(gè)成員：

struct dirent {    ino_t     d_ino;                  /* i-node number */    char     d_name[NAME_MAX + 1];    /*null-terminated filename */}

DIR結(jié)構(gòu)是一個(gè)內(nèi)部結(jié)構(gòu)，上述6個(gè)函數(shù)用這個(gè)內(nèi)部結(jié)構(gòu)保存當(dāng)前正被讀的目錄的有關(guān)信息。其作用類似與FILE結(jié)構(gòu)。FILE結(jié)構(gòu)由標(biāo)準(zhǔn)I/O庫維護(hù)。

由opendir返回的指向DIR結(jié)構(gòu)的指針由另外5個(gè)函數(shù)使用。opendir執(zhí)行初始化操作，使第一個(gè)readdir讀目錄中的第一個(gè)目錄項(xiàng)。目錄中各目錄項(xiàng)的順序與實(shí)現(xiàn)有關(guān)。它們通常并不按字母順序排序。

程序清單4-7 遞歸降序遍歷目錄層次結(jié)構(gòu)，并按文件類型計(jì)數(shù)

[root@localhost apue]# cat -b PRog4-7.c     1  #include "apue.h"     2  #include <dirent.h>     3  #include <limits.h>     4  #include <errno.h>     5  #ifdef PATH_MAX     6  static int pathmax = PATH_MAX;     7  #else     8  static int pathmax = 0;     9  #endif    10  #define SUSV3 200112L    11  static long posix_version = 0;    12  /* If PATH_MAX is indeterminate, no guarantee  this is adequate */    13  #define PATH_MAX_GUESS 1024    14  char *    15  path_alloc(int *sizep) /* also return allocated size, if nonull */    16  {    17          char *ptr;    18          int size;    19          if(posix_version == 0)    20                  posix_version = sysconf(_SC_VERSION);    21    22          if(pathmax == 0) {   /* first time trough */    23                  errno = 0;    24                  if((pathmax = pathconf("/", _PC_PATH_MAX)) < 0) {    25                          if(errno == 0)    26                                  pathmax = PATH_MAX_GUESS;  /* it's indeterminate */    27                          else    28                                  err_sys("pathconf error for _PC_PATH_MAX");    29                  } else {    30                          pathmax++;    /* add one since it's relative to root */    31                  }    32          }    33          if(posix_version < SUSV3)    34                  size = pathmax + 1;    35          else    36                  size = pathmax;    37    38          if((ptr = malloc(size)) == NULL)    39                  err_sys("malloc error for pathname");    40          if(sizep != NULL)    41                  *sizep = size;    42          return(ptr);    43  }    44  /* function type that is called for each filename */    45  typedef int Myfunc( const char *, const struct stat *, int );    46  static Myfunc   myfunc;    47  static int      myftw( char *, Myfunc * );    48  static int      dopath( Myfunc * );    49  static long nreg, ndir, nblk, nchr, nfifo, nslink, nsock, ntot;    50  int    51  main( int argc, char *argv[] )    52  {    53          int ret;    54    55          if( argc != 2 )    56                  err_quit( "usage: ftw <starting-pathname>" );    57    58          ret = myftw( argv[1], myfunc );         /* does it all */    59          ntot = nreg + ndir + nblk + nchr + nfifo + nslink + nsock;    60          if( ntot == 0 )    61                  ntot = 1;       /* avoid divide by 0; print 0 for all counts */    62          printf( "regular files  = %7ld, %5.2f %%/n", nreg, nreg*100.0/ntot );    63          printf( "directories    = %7ld, %5.2f %%/n", ndir, ndir*100.0/ntot );    64          printf( "block special  = %7ld, %5.2f %%/n", nblk, nblk*100.0/ntot );    65          printf( "char special   = %7ld, %5.2f %%/n", nchr, nchr*100.0/ntot );    66          printf( "FIFOs          = %7ld, %5.2f %%/n", nfifo, nfifo*100.0/ntot );    67          printf( "symbolic links = %7ld, %5.2f %%/n", nslink, nslink*100.0/ntot );    68          printf( "sockets                = %7ld, %5.2f %%/n", nsock, nsock*100.0/ntot );    69          exit( ret );    70  }    71  /*    72  * Descend throuth the hierarchy, starting at "pathname".    73  * The caller's func() is called for every file.    74  */    75  #define FTW_F   1       /* file other than directory */    76  #define FTW_D   2       /* directory */    77  #define FTW_DNR 3       /* directory that can't be read */    78  #define FTW_NS  4       /* file that we can't stat */    79  static char * fullpath; /*contains full pathname for every file */    80  static int    81  myftw( char *pathname, Myfunc *func )    82  {    83          int len;    84          fullpath = path_alloc( &len );  /* malloc's for PATH_MAX + 1 bytes */    85                                          /* program_list 2-3 */    86          strncpy( fullpath, pathname, len );     /* protect against */    87          fullpath[len - 1] = 0;    88          return(dopath(func));    89  }    90  /*    91  * Descend through the hierarchy, starting at "fullpath".    92  * If "fullpath" is anything other than a directory, we lstat() it,    93  * call func(), and return. For a directory, we call ourself     94  * recursively for each name in the directory.    95  */    96  static int    97  dopath( Myfunc *func )    98  {    99          struct stat     statbuf;   100          struct dirent   *dirp;   101          DIR             *dp;   102          int             ret;   103          char            *ptr;   104          if( lstat( fullpath, &statbuf ) < 0 )   /* stat error */   105                  return( func(fullpath, &statbuf, FTW_NS) );   106          if( S_ISDIR(statbuf.st_mode) == 0)      /* not a directory */   107                  return( func(fullpath, &statbuf, FTW_F) );   108          /*   109          * It's a directory. First call func() for the directory,   110          * then process each filename in the directory.   111          */   112          if((ret = func(fullpath, &statbuf, FTW_D)) != 0)   113                  return(ret);   114          ptr = fullpath + strlen(fullpath);      /* point to end of fullpath */   115          *ptr++ = '/';   116          *ptr = 0;   117          if((dp = opendir(fullpath)) == NULL)    /* can't read directory */   118                  return(func(fullpath, &statbuf, FTW_DNR));   119          while((dirp = readdir(dp)) != NULL)   120          {   121                  if(strcmp(dirp->d_name, ".") == 0 ||   122                     strcmp(dirp->d_name, "..") == 0)   123                          continue;       /* ignore dot and dot-dot */   124   125                  strcpy(ptr, dirp->d_name);      /*append name after slash */   126          //      if((ret = dopath(func)) != 0)   /* recursive */   127          //              break;                  /* time to leave */   128                  dopath(func);   129          }   130          ptr[-1] = 0;    /* erase everything from slash onwards */   131          if(closedir(dp) < 0)   132                  err_ret("can't close directory %s", fullpath);   133          return(ret);   134  }   135  static int   136  myfunc(const char *pathname, const struct stat *statptr, int type)   137  {   138          switch(type)   139          {   140                  case FTW_F:   141                          switch(statptr->st_mode & S_IFMT)   142                          {   143                                  case S_IFREG:   nreg++;         break;   144                                  case S_IFBLK:   nblk++;         break;   145                                  case S_IFCHR:   nchr++;         break;   146                                  case S_IFIFO:   nfifo++;        break;   147                                  case S_IFLNK:   nslink++;       break;   148                                  case S_IfsoCK:  nsock++;        break;   149                                  case S_IFDIR:   150                                          err_dump("for S_IFDIR for %s", pathname);   151                                          /* directories should have type = FTW_D */   152                          }   153                          break;   154                  case FTW_D:   155                          ndir++;   156                          break;   157                  case FTW_DNR:   158                          err_ret("can't read directory %s", pathname);   159                          break;   160                  case FTW_NS:   161                          err_ret("stat error for %s", pathname);   162                          break;   163                  default:   164                          err_dump("unknown type %d for pathname %s", type, pathname);   165          }   166          return( 0 );   167  }

程序運(yùn)行結(jié)果：

[root@localhost apue]# ./prog4-7 /home/zhu/testregular files   =       3, 60.00 %directories     =       2, 40.00 %block special   =       0,  0.00 %char special    =       0,  0.00 %FIFOs           =       0,  0.00 %symbolic links  =       0,  0.00 %sockets         =       0,  0.00 %

上面的源程序代碼中有一個(gè)不理解的地方，第126-127行（這是APUE書中原來的代碼）。希望路過的有緣人可以指點(diǎn)一二，小弟不勝感激。將這兩行替換為128行，這樣能夠理解，而且程序正確執(zhí)行。

本篇博文內(nèi)容摘自《UNIX環(huán)境高級編程》（第二版），僅作個(gè)人學(xué)習(xí)記錄所用。關(guān)于本書可參考：http://www.apuebook.com/。