函数1：path_alloc函数为路径名动态地分配空间/*这个跟版本关系很大*/#include "apue.h"#include <errno.h>#include <limits.h>#ifdef PATH_MAX /*如果定义了路径名的最大长度*/static int pathmax = PATH_MAX; /*将它赋予我们自己定义的变量pathmax*/#elsestatic int pathmax = 0; /*否则该位置0*/#endif /*上面那个if结束*/#define SUSV3 200112Lstatic long posix_version = 0;/* If PATH_MAX is indeterminate, no guarantee this is adequate */#define PATH_MAX_GUESS 1024char *path_alloc(int *sizep) /* also return allocated size, if nonnull */ {char *ptr;int size;if (posix_version == 0)posix_version = sysconf(_SC_VERSION);if (pathmax == 0){ /* first time through */errno = 0;if ((pathmax = pathconf("/", _PC_PATH_MAX)) < 0)/*PATH_MAX 相对路径名的最大字节数，包括null _PC_PATH_MAX*/{if (errno == 0)pathmax = PATH_MAX_GUESS; /* 确认是未决的就使用我们猜测的值 */ else /*errno不为0说明pathconf执行错误*/err_sys("pathconf error for _PC_PATH_MAX");}else{pathmax++; /* 没有/说明是根目录，它也有一个路径 */}}if (posix_version < SUSV3) /*size和版本有关*/size = pathmax + 1;elsesize = pathmax;if ((ptr = malloc(size)) == NULL) /*分配空间失败则返回空指针*/err_sys("malloc error for pathname");if (sizep != NULL) *sizep = size;/*如果传入的参数不是null，说明它需要分配空间，把size分给它*/return(ptr); /*返回这段空间的首地址指针*/}递归降序遍历目录层次结构，并按文件类型计数#include <sys/types.h>#include <sys/stat.h>#include <dirent.h>#include <limits.h>#include "ourhdr.h"typedef int Myfunc(const char *, const struct stat *, int);/* function type that's called for each filename */static Myfunc myfunc;static int myftw(char *, Myfunc *);static int dopath(Myfunc *);static long nreg, ndir, nblk, nchr, nfifo, nslink, nsock, ntot;intmain(int argc, char *argv[]){int ret;if (argc != 2) /*输入的参数个数不为2，提醒输入的格式*/err_quit("usage: ftw <starting-pathname>");ret = myftw(argv[1], myfunc); /* 解析整个完整的路径 */if ( (ntot = nreg + ndir + nblk + nchr + nfifo + nslink + nsock) == 0) /*一个文件也没有，这个类每个都是0*/ntot = 1;/*特殊技巧，分母为0，置1也无妨，只要非0即可 0/1=0*/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 /* 不是目录的文件 */#define FTW_D 2 /* 目录*/#define FTW_DNR 3 /* 不可以读的文件 */#define FTW_NS 4 /* 不能被stat的文件 */static char *fullpath;/* 包含每个文件的完整路径名 */static int/* 我们返回任何func()函数返回的*/myftw(char *pathname, Myfunc *func){fullpath = path_alloc(NULL); //这里采用默认的path_alloc大小*/ /*这里调用path_alloc函数，所以要gcc 2.c error.c path_alloc.c -o 2*/ strcpy(fullpath, pathname);//不用像课本那样，strcpy自动在结束的位置补上/n/* 为fullpath变量初始化 */return(dopath(func));}/** 通过层次进行下降操作，我们从全路径开始* 如果是一个绝对的路径而非一个目录，我们调用lstat函数* call func(), and return. For a directory, we call ourself* recursively for each name in the directory.*/static int dopath(Myfunc* func){struct stat statbuf; /*statbuf是stat结构体的实例*/struct dirent *dirp; /*为获取文件夹目录所用的结构体*/DIR *dp; /*与目录有关的指针*/int ret;char *ptr; /*保存要显示的字符串*/if (lstat(fullpath, &statbuf) < 0)return(func(fullpath, &statbuf, FTW_NS));/*lstat可以查询类型，之后出来S_...那些*/if (S_ISDIR(statbuf.st_mode) == 0)/*返回1说明是目录，没返回1说明不是,那就不用再做了*/return(func(fullpath, &statbuf, FTW_F));/** 它是一个目录,首先呼叫func（）得到目录* 然后执行目录中的每一个文件*/if ( (ret = func(fullpath, &statbuf, FTW_D)) != 0)return(ret);ptr = fullpath + strlen(fullpath);/* fullpath为文件的首地址，加上个长度的单位指向*/*ptr++ = '/';*ptr = 0; /*路径的末尾添加/0代表结束*/if ( (dp = opendir(fullpath)) == NULL)/*成功返回指针，失败null*/ return(func(fullpath, &statbuf, FTW_DNR));while ( (dirp = readdir(dp)) != NULL) {if (strcmp(dirp->d_name, ".") == 0 ||strcmp(dirp->d_name, "..") == 0)continue;/*忽略.和..*/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)/*closedir成功返回0,出错返回-1*/err_ret("can't close directory %s", fullpath);return(ret);}static intmyfunc(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);}3.lstat函数int lstat(const char *pathname, struct stat *buf);文件类型—用<sys/stat.h>中说明的文件类型宏测试S_ISREG(mode) == 1 正规文件(S_IFREG)S_ISDIR(mode) == 1 目录文件(S_IFDIR)S_ISCHR(mode) == 1 字符特殊文件(S_IFCHR)S_ISBLK(mode) == 1 块特殊文件(S_IFBLK)S_ISFIFO(mode) == 1 管道或FIFO文件(S_IFFIFO)S_ISLNK(mode) == 1 符号链接(S_IFLNK)S_ISSOCK(mode) == 1 套接口(S_IFSOCK)针对每个命令参数打印其文件类型#include <sys/types.h>#include <sys/stat.h>#include "ourhdr.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 **";/*不是以上这几类，那是未知模式*/printf("%s\n", ptr);/*打印类型字符串*/}exit(0);}。
