Gets the length of a file.
Both _filelength and _filelengthi64 return the file length, in bytes, of the target file associated with fd. If fd is an invalid file descriptor, this function invokes the invalid parameter handler, as described in Parameter Validation. If execution is allowed to continue, both functions return –1L to indicate an error and set errno to EBADF.
For more compatibility information, see Compatibility in the Introduction.