#include <fcntl.h> #include <sys/stat.h> int fstatat(int fd, const char *restrict path, struct stat *restrict buf, int flag); int lstat(const char *restrict path, struct stat *restrict buf); int stat(const char *restrict path, struct stat *restrict buf);
If the named file is a symbolic link, the stat() function shall continue pathname resolution using the contents of the symbolic link, and shall return information pertaining to the resulting file if the file exists.
The buf argument is a pointer to a stat structure, as defined in the <sys/stat.h> header, into which information is placed concerning the file.
The stat() function shall update any time-related fields (as described in the Base Definitions volume of POSIX.1-2017, Section 4.9, File Times Update), before writing into the stat structure.
If the named file is a shared memory object, the implementation shall update in the stat structure pointed to by the buf argument the st_uid, st_gid, st_size, and st_mode fields, and only the S_IRUSR, S_IWUSR, S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH file permission bits need be valid. The implementation may update other fields and flags.
If the named file is a typed memory object, the implementation shall update in the stat structure pointed to by the buf argument the st_uid, st_gid, st_size, and st_mode fields, and only the S_IRUSR, S_IWUSR, S_IRGRP, S_IWGRP, S_IROTH, and S_IWOTH file permission bits need be valid. The implementation may update other fields and flags.
For all other file types defined in this volume of POSIX.1-2017, the structure members st_mode, st_ino, st_dev, st_uid, st_gid, st_atim, st_ctim, and st_mtim shall have meaningful values and the value of the member st_nlink shall be set to the number of links to the file.
The lstat() function shall be equivalent to stat(), except when path refers to a symbolic link. In that case lstat() shall return information about the link, while stat() shall return information about the file the link references.
For symbolic links, the st_mode member shall contain meaningful information when used with the file type macros. The file mode bits in st_mode are unspecified. The structure members st_ino, st_dev, st_uid, st_gid, st_atim, st_ctim, and st_mtim shall have meaningful values and the value of the st_nlink member shall be set to the number of (hard) links to the symbolic link. The value of the st_size member shall be set to the length of the pathname contained in the symbolic link not including any terminating null byte.
The fstatat() function shall be equivalent to the stat() or lstat() function, depending on the value of flag (see below), except in the case where path specifies a relative path. In this case the status shall be retrieved from a file relative to the directory associated with the file descriptor fd instead of the current working directory. If the access mode of the open file description associated with the file descriptor is not O_SEARCH, the function shall check whether directory searches are permitted using the current permissions of the directory underlying the file descriptor. If the access mode is O_SEARCH, the function shall not perform the check.
Values for flag are constructed by a bitwise-inclusive OR of flags from the following list, defined in <fcntl.h>:
If fstatat() is passed the special value AT_FDCWD in the fd parameter, the current working directory shall be used and the behavior shall be identical to a call to stat() or lstat() respectively, depending on whether or not the AT_SYMLINK_NOFOLLOW bit is set in flag.
The fstatat() function shall fail if:
These functions may fail if:
The fstatat() function may fail if:
The following sections are informative.
The following example shows how to obtain file status information for a file named /home/cnd/mod1. The structure variable buffer is defined for the stat structure.
#include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> struct stat buffer; int status; ... status = stat("/home/cnd/mod1", &buffer);
The following example fragment gets status information for each entry in a directory. The call to the stat() function stores file information in the stat structure pointed to by statbuf. The lines that follow the stat() call format the fields in the stat structure for presentation to the user of the program.
#include <sys/types.h> #include <sys/stat.h> #include <dirent.h> #include <pwd.h> #include <grp.h> #include <time.h> #include <locale.h> #include <langinfo.h> #include <stdio.h> #include <stdint.h> struct dirent *dp; struct stat statbuf; struct passwd *pwd; struct group *grp; struct tm *tm; char datestring[256]; ... /* Loop through directory entries. */ while ((dp = readdir(dir)) != NULL) { /* Get entry's information. */ if (stat(dp->d_name, &statbuf) == -1) continue; /* Print out type, permissions, and number of links. */ printf("%10.10s", sperm (statbuf.st_mode)); printf("%4d", statbuf.st_nlink); /* Print out owner's name if it is found using getpwuid(). */ if ((pwd = getpwuid(statbuf.st_uid)) != NULL) printf(" %-8.8s", pwd->pw_name); else printf(" %-8d", statbuf.st_uid); /* Print out group name if it is found using getgrgid(). */ if ((grp = getgrgid(statbuf.st_gid)) != NULL) printf(" %-8.8s", grp->gr_name); else printf(" %-8d", statbuf.st_gid); /* Print size of file. */ printf(" %9jd", (intmax_t)statbuf.st_size); tm = localtime(&statbuf.st_mtime); /* Get localized date string. */ strftime(datestring, sizeof(datestring), nl_langinfo(D_T_FMT), tm); printf(" %s %s\n", datestring, dp->d_name); }
The following example shows how to obtain status information for a symbolic link named /modules/pass1. The structure variable buffer is defined for the stat structure. If the path argument specified the pathname for the file pointed to by the symbolic link (/home/cnd/mod1), the results of calling the function would be the same as those returned by a call to the stat() function.
#include <sys/stat.h> struct stat buffer; int status; ... status = lstat("/modules/pass1", &buffer);
The purpose of the fstatat() function is to obtain the status of files in directories other than the current working directory without exposure to race conditions. Any part of the path of a file could be changed in parallel to a call to stat(), resulting in unspecified behavior. By opening a file descriptor for the target directory and using the fstatat() function it can be guaranteed that the file for which status is returned is located relative to the desired directory.
The Base Definitions volume of POSIX.1-2017, Section 4.9, File Times Update, <fcntl.h>, <sys_stat.h>, <sys_types.h>
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