fstat64

fstat64 is a variant of the POSIX fstat function used to obtain status information about an open file referred to by a file descriptor, with emphasis on large-file support. It is typically provided on systems that historically required 64-bit file sizes on 32-bit architectures. On modern 64-bit systems, the regular fstat and the related stat structures already accommodate large files, and fstat64 may be a compatibility symbol rather than a separate necessity.

The function signature is generally int fstat64(int fd, struct stat64 *buf); on success it fills the provided stat64 structure with information about the file, and on error returns -1 while setting errno. The struct stat64 mirrors the fields found in struct stat but uses 64-bit types for size-related data to support files larger than 2 GiB. Expected fields include device and inode information, mode and ownership data, a 64-bit file size, block size and block counts, and timestamps for access, modification, and status changes.

Usage of fstat64 is mainly for maintaining compatibility with older codebases and systems that expose a distinct 64-bit variant of the stat interface. Developers writing portable code should prefer the standard fstat and the regular struct stat when possible, relying on the system’s large-file support to expose 64-bit sizes transparently. In environments that do provide fstat64, include the appropriate headers (such as <sys/stat.h>) and ensure the target platform supports the 64-bit stat64 variant.

See also stat64, fstat, lstat, and stat for related file-status operations.