In Section 4.21, our version of ftw never changes its directory. Modify this routine so that each time it encounters a directory, it does a chdir to that directory, allowing it to use the filename and not the pathname for each call to lstat. When all the entries in a directory have been processed, execute chdir(".."). Compare the time used by this version and the version in the text.
主要是修改dopath()函数，每当找到一个新的目录后，就使用chdir()把current working directory设置成那个目录，这样路径搜索就会首先从current working directory开始。
还把fullpath这个全局变量改成了filename，因为不再需要完整路径。
修改的地方（与fig4.22比较）：
· myftw函数：把fullpath改为filename
· dopath函数改动很多，标记“//改”的地方
main 函数
#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; /* 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); }
myftw函数：
/* * Descent 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 than can't be read */ #define FTW_NS 4 /* file that we can't stat */ static char *filename; /* contains full pathname for every file */ static int myftw(char *pathname, Myfunc *func) { int len; filename = path_alloc(&len); strncpy(filename, pathname, len); filename[len-1] = 0; return dopath(func); }
dopath函数：
static int dopath(Myfunc *func) { struct stat statbuf; struct dirent *dirp; DIR *dp; int ret; //char *ptr; if (lstat(filename, &statbuf) < 0) return func(filename, &statbuf, FTW_NS); if (S_ISDIR(statbuf.st_mode) == 0) return func(filename, &statbuf, FTW_F); if ( (ret = func(filename, &statbuf, FTW_D)) != 0) return ret; /* ptr = filename + strlen(filename); *ptr++ = '/'; *ptr = 0; */ if (chdir(filename) < 0) //改 err_quit("chdir error"); if ( (dp = opendir(".")) == NULL) //改 return func(".", &statbuf, FTW_DNR); //改 while ( (dirp = readdir(dp)) != NULL) { /* read dir entry one by one */ if (strcmp(dirp->d_name, ".") == 0 || strcmp(dirp->d_name, "..") == 0) continue; strcpy(filename, dirp->d_name); //改 if ( (ret = dopath(func)) != 0) break; } //ptr[-1] = 0; if (closedir(dp) < 0) err_ret("can't close directory %s", filename); if (chdir("..") < 0) //改 err_quit("chdir to .. error"); return ret; }
myfunc函数：
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; }
注意：全局变量和函数之前使用static修饰，只表示这个变量或者函数不能在其他文件中引用。没有其他别的意思。
chdir(“.."); 这个函数中的参数不必是"./temp/”这样的类型，即最后的斜杠不需要。它会改变current working directory，这个应该由什么东西维护，表示现在正在工作的目录，搜索的时候就会首先从这里搜索。
opendir(“."); 这个函数的参数也和上面函数一样，最后的斜杠不需要的。写成opendir(“./")没有必要。
readdir()返回的dirp中的dirp->d_name在kdbg中显示得比较奇怪，首先会显示它的正确信息，比如"."，之后会跟一大溜乱七八糟的数字。没关系的。