tail head cat sleep
QR code linking to this page

Manual Pages  — FTW


ftw – traverse (walk) a file tree



#include <ftw.h>

ftw(const char *path, int (*fn)(const char *, const struct stat *, int), int maxfds);

nftw(const char *path, int (*fn)(const char *, const struct stat *, int, struct FTW *), int maxfds, int flags);


The ftw() and nftw() functions traverse (walk) the directory hierarchy rooted in path. For each object in the hierarchy, these functions call the function pointed to by fn. The ftw() function passes this function a pointer to a NUL -terminated string containing the name of the object, a pointer to a stat structure corresponding to the object, and an integer flag. The nftw() function passes the aforementioned arguments plus a pointer to a FTW structure as defined by <ftw.h> (shown below):
struct FTW {
    int base;   /* offset of basename into pathname */
    int level;  /* directory depth relative to starting point */

Possible values for the flag passed to fn are:
FTW_F A regular file.
FTW_D A directory being visited in pre-order.
  A directory which cannot be read. The directory will not be descended into.
FTW_DP A directory being visited in post-order (nftw() only ).
FTW_NS A file for which no stat(2) information was available. The contents of the stat structure are undefined.
FTW_SL A symbolic link.
  A symbolic link with a non-existent target (nftw() only ).

The ftw() function traverses the tree in pre-order. That is, it processes the directory before the directory's contents.

The maxfds argument specifies the maximum number of file descriptors to keep open while traversing the tree. It has no effect in this implementation.

The nftw() function has an additional flags argument with the following possible values:
FTW_PHYS Physical walk, do not follow symbolic links.
  The walk will not cross a mount point.
  Process directories in post-order. Contents of a directory are visited before the directory itself. By default, nftw() traverses the tree in pre-order.
  Change to a directory before reading it. By default, nftw() will change its starting directory. The current working directory will be restored to its original value before nftw() returns.


If the tree was traversed successfully, the ftw() and nftw() functions return 0. If the function pointed to by fn returns a non-zero value, ftw() and nftw() will stop processing the tree and return the value from fn. Both functions return -1 if an error is detected.


Following there is an example that shows how nftw can be used. It traverses the file tree starting at the directory pointed by the only program argument and shows the complete path and a brief indicator about the file type.
#include <ftw.h>
#include <stdio.h>
#include <sysexits.h>

int nftw_callback(const char *path, const struct stat *sb, int typeflag, struct FTW *ftw) {         char type;

        switch(typeflag) {         case FTW_F:                 type = 'F';                 break;         case FTW_D:                 type = 'D';                 break;         case FTW_DNR:                 type = '-';                 break;         case FTW_DP:                 type = 'd';                 break;         case FTW_NS:                 type = 'X';                 break;         case FTW_SL:                 type = 'S';                 break;         case FTW_SLN:                 type = 's';                 break;         default:                 type = '?';                 break;         }

        printf("[%c] %s , type, path);

        return (0); }

int main(int argc, char **argv) {

        if (argc != 2) {                 printf("Usage %s <directory> , argv[0]);                 return (EX_USAGE);         } else                 return (nftw(argv[1], nftw_callback, /* UNUSED */ 1, 0)); }


The ftw() and nftw() functions may fail and set errno for any of the errors specified for the library functions close(2), open(2), stat(2), malloc(3), opendir(3) and readdir(3). If the FTW_CHDIR flag is set, the nftw() function may fail and set errno for any of the errors specified for chdir(2). In addition, either function may fail and set errno as follows:
  The maxfds argument is less than 1.


chdir(2), close(2), open(2), stat(2), fts(3), malloc(3), opendir(3), readdir(3)


The ftw() and nftw() functions conform to IEEE Std 1003.1-2001 ("POSIX.1").


These functions first appeared in AT&T V.3 . Their first FreeBSD appearance was in FreeBSD 5.3 .


The maxfds argument is currently ignored.

FTW (3) March 12, 2020

tail head cat sleep
QR code linking to this page

Please direct any comments about this manual page service to Ben Bullock. Privacy policy.

On two occasions I have been asked [by members of Parliament], 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question.
— Charles Babbage