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我在阅读apue的时候,遇到了一个问题,
这个例子是遍历目录的例子,源代码在
http://book.chinaunix.net/specia ... /ch04lev1sec21.html
为了方便阅读,我也贴上面了,如果格式不习惯,或者更多的信息参见前面的网址。
问题是,
1,myfunc是用typedef定义的函数类型的变量,那么,这个变量是否代表一个函数?
2,如果1成立,怎样引用myfunc所代表的函数?
3,在例子里面,把 myfunc作为其他函数的参数了,那么,myfunc本身的参数是从哪里传进来的?
总结如上问题,关键就是,如何获取myyfunc的参数信息?- #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);
- }
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