--- name: "nftw" section: "3p" platform: "linux" package: "man-pages" version: "6.19-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/nftw/3p" --- # nftw(3p) walk a file tree ## PROLOG This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. ## NAME nftw — walk a file tree ## SYNOPSIS ``` #include ``` int nftw(const char \**path*, int (\**fn*)(const char \*,\ const struct stat \*, int, struct FTW \*), int *fd\_limit*, int *flags*); ## DESCRIPTION The *nftw*() function shall recursively descend the directory hierarchy rooted in *path*. The *nftw*() function has a similar effect to *ftw*() except that it takes an additional argument *flags*, which is a bitwise-inclusive OR of zero or more of the following flags: - FTW\_CHDIR If set, *nftw*() shall change the current working directory to each directory as it reports files in that directory. If clear, *nftw*() shall not change the current working directory. - FTW\_DEPTH If set, *nftw*() shall report all files in a directory before reporting the directory itself. If clear, *nftw*() shall report any directory before reporting the files in that directory. - FTW\_MOUNT If set, *nftw*() shall only report files in the same file system as *path*. If clear, *nftw*() shall report all files encountered during the walk. - FTW\_PHYS If set, *nftw*() shall perform a physical walk and shall not follow symbolic links. If FTW\_PHYS is clear and FTW\_DEPTH is set, *nftw*() shall follow links instead of reporting them, but shall not report any directory that would be a descendant of itself. If FTW\_PHYS is clear and FTW\_DEPTH is clear, *nftw*() shall follow links instead of reporting them, but shall not report the contents of any directory that would be a descendant of itself. At each file it encounters, *nftw*() shall call the user-supplied function *fn* with four arguments: - \* The first argument is the pathname of the object. - \* The second argument is a pointer to the **stat** buffer containing information on the object, filled in as if *fstatat*(), *stat*(), or *lstat*() had been called to retrieve the information. - \* The third argument is an integer giving additional information. Its value is one of the following: - FTW\_D The object is a directory. - FTW\_DNR The object is a directory that cannot be read. The *fn* function shall not be called for any of its descendants. - FTW\_DP The object is a directory and subdirectories have been visited. (This condition shall only occur if the FTW\_DEPTH flag is included in *flags*.) - FTW\_F The object is a non-directory file. - FTW\_NS The *stat*() function failed on the object because of lack of appropriate permission. The **stat** buffer passed to *fn* is undefined. Failure of *stat*() for any other reason is considered an error and *nftw*() shall return -1. - FTW\_SL The object is a symbolic link. (This condition shall only occur if the FTW\_PHYS flag is included in *flags*.) - FTW\_SLN The object is a symbolic link that does not name an existing file. (This condition shall only occur if the FTW\_PHYS flag is not included in *flags*.) - \* The fourth argument is a pointer to an **FTW** structure. The value of **base** is the offset of the object's filename in the pathname passed as the first argument to *fn*. The value of **level** indicates depth relative to the root of the walk, where the root level is 0. The results are unspecified if the application-supplied *fn* function does not preserve the current working directory. The argument *fd\_limit* sets the maximum number of file descriptors that shall be used by *nftw*() while traversing the file tree. At most one file descriptor shall be used for each directory level. The *nftw*() function need not be thread-safe. ## RETURN VALUE The *nftw*() function shall continue until the first of the following conditions occurs: - \* An invocation of *fn* shall return a non-zero value, in which case *nftw*() shall return that value. - \* The *nftw*() function detects an error other than **\[EACCES\]** (see FTW\_DNR and FTW\_NS above), in which case *nftw*() shall return -1 and set *errno* to indicate the error. - \* The tree is exhausted, in which case *nftw*() shall return 0. ## ERRORS The *nftw*() function shall fail if: - **EACCES** Search permission is denied for any component of *path* or read permission is denied for *path*, or *fn* returns -1 and does not reset *errno*. - **ELOOP** A loop exists in symbolic links encountered during resolution of the *path* argument. - **ENAMETOOLONG** The length of a component of a pathname is longer than {NAME\_MAX}. - **ENOENT** A component of *path* does not name an existing file or *path* is an empty string. - **ENOTDIR** A component of *path* names an existing file that is neither a directory nor a symbolic link to a directory. - **EOVERFLOW** A field in the **stat** structure cannot be represented correctly in the current programming environment for one or more files found in the file hierarchy. The *nftw*() function may fail if: - **ELOOP** More than {SYMLOOP\_MAX} symbolic links were encountered during resolution of the *path* argument. - **EMFILE** All file descriptors available to the process are currently open. - **ENAMETOOLONG** The length of a pathname exceeds {PATH\_MAX}, or pathname resolution of a symbolic link produced an intermediate result with a length that exceeds {PATH\_MAX}. - **ENFILE** Too many files are currently open in the system. In addition, *errno* may be set if the function pointed to by *fn* causes *errno* to be set. *The following sections are informative.* ## EXAMPLES The following program traverses the directory tree under the path named in its first command-line argument, or under the current directory if no argument is supplied. It displays various information about each file. The second command-line argument can be used to specify characters that control the value assigned to the *flags* argument when calling *nftw*(). ``` #include #include #include #include #include ``` static int display\_info(const char \*fpath, const struct stat \*sb,\ int tflag, struct FTW \*ftwbuf) {\ printf("%-3s %2d %7jd %-40s %d %s\\n",\ (tflag == FTW\_D) ? "d" : (tflag == FTW\_DNR) ? "dnr" :\ (tflag == FTW\_DP) ? "dp" : (tflag == FTW\_F) ?\ (S\_ISBLK(sb-\>st\_mode) ? "f b" :\ S\_ISCHR(sb-\>st\_mode) ? "f c" :\ S\_ISFIFO(sb-\>st\_mode) ? "f p" :\ S\_ISREG(sb-\>st\_mode) ? "f r" :\ S\_ISSOCK(sb-\>st\_mode) ? "f s" : "f ?") :\ (tflag == FTW\_NS) ? "ns" : (tflag == FTW\_SL) ? "sl" :\ (tflag == FTW\_SLN) ? "sln" : "?",\ ftwbuf-\>level, (intmax\_t) sb-\>st\_size,\ fpath, ftwbuf-\>base, fpath + ftwbuf-\>base);\ return 0; /\* To tell nftw() to continue \*/ } int main(int argc, char \*argv\[\]) {\ int flags = 0; if (argc \> 2 && strchr(argv\[2\], 'd') != NULL)\ flags \|= FTW\_DEPTH;\ if (argc \> 2 && strchr(argv\[2\], 'p') != NULL)\ flags \|= FTW\_PHYS; if (nftw((argc \< 2) ? "." : argv\[1\], display\_info, 20, flags) == -1)\ {\ perror("nftw");\ exit(EXIT\_FAILURE);\ } exit(EXIT\_SUCCESS); } ## APPLICATION USAGE The *nftw*() function may allocate dynamic storage during its operation. If *nftw*() is forcibly terminated, such as by *longjmp*() or *siglongjmp*() being executed by the function pointed to by *fn* or an interrupt routine, *nftw*() does not have a chance to free that storage, so it remains permanently allocated. A safe way to handle interrupts is to store the fact that an interrupt has occurred, and arrange to have the function pointed to by *fn* return a non-zero value at its next invocation. ## RATIONALE None. ## FUTURE DIRECTIONS None. ## SEE ALSO *fdopendir()*, *fstatat()*, *readdir()* The Base Definitions volume of POSIX.1‐2017, ***\*** ## COPYRIGHT Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html . 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