fstat

Syntax

#include <sys/stat.h>

int fstat(int file, struct stat *sbuf);

Description

This function obtains the status of the open file file and stores it in sbuf. See section stat for the description of struct stat fields.

Return Value

Zero on success, nonzero on failure (and errno set).

Portability

not ANSI, POSIX

Example

struct stat s;
fstat(fileno(stdin), &s);
if (S_ISREG(s.st_mode))
  puts("STDIN is a redirected disk file");
else if (S_ISCHR(s.st_mode))
  puts("STDIN is a character device");

Bugs

If a file was open in write-only mode, its execute mode bits might be incorrectly reported as if the file were non-executable. This is because some executables are only recognized by reading their first two bytes, which cannot be done for files open in write-only mode.

For fstat() to return valid info, you should make sure that all the data written to the file has been delivered to the operating system, e.g. by calling fflush(). Otherwise, the buffering of the library I/O functions might cause stale info to be returned.

Implementation Notes

Supplying a 100% Unix-compatible f?stat() functions under DOS is an implementation nightmare. The following notes describe some of the obscure points specific to their behavior in DJGPP.

1. The `drive' for character devices (like con, /dev/null and others is returned as -1. For drives networked by Novell Netware, it is returned as -2.

2. The starting cluster number of a file serves as its inode number. For files whose starting cluster number is inaccessible (empty files, files on networked drives, etc.) the st_inode field will be invented in a way which guarantees that no two different files will get the same inode number (thus it is unique). This invented inode will also be different from any real cluster number of any local file. However, only for local, non-empty files/directories the inode is guaranteed to be consistent between stat() and fstat() function calls.

3. The WRITE access mode bit is set only for the user (unless the file is read-only, hidden or system). EXECUTE bit is set for directories, files which can be executed from the DOS prompt (batch files, .com, .dll and .exe executables) or run by go32 extender. For files which reside on networked drives under Novell Netware, this can sometimes fail, in which case only the read access bit is set.

4. Size of directories is reported as the number of its files (sans `.' and `..' entries) multiplied by 32 bytes (the size of directory entry).

5. Time stamp for root directories is taken from the volume label entry, if that's available; otherwise, it is reported as 1-Jan-1980.

6. The variable section _djstat_flags controls what hard-to-get fields of struct stat are needed by the application.

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