Determining the size of a file larger than 4GB

Question

The code currently does this and the fgetpos does handle files larger than 4GB but the seek returns an error, so any idea how to seek to the end of a file > 4GB?

fpos_t currentpos;

sok=fseek(fp,0,SEEK_END);
assert(sok==0,"Seek error!");

fgetpos(fp,&currentpos);
m_filesize=currentpos;

Toothpick

Just out of curiosity, are you sure that fgetpos is working correctly if you haven't gotten to the end of the file? – Chappell

fpos_t is not an integer type so the last line is invalid. – Pringle

Answer 1

If you're in Windows, you want GetFileSizeEx (MSDN). The return value is a 64bit int.

On linux stat64 (manpage) is correct. fstat if you're working with a FILE*.

Lebna

Answer 2

Ignore all the answers with "64" appearing in them. On Linux, you should add -D_FILE_OFFSET_BITS=64 to your CFLAGS and use the fseeko and ftello functions which take/return off_t values instead of long. These are not part of C but POSIX. Other (non-Linux) POSIX systems may need different options to ensure that off_t is 64-bit; check your documentation.

Pringle

Could you provide references? – Bernadette

@qed: "Not part of POSIX": See pubs.opengroup.org/onlinepubs/9699919799/functions/… ; Usage of -D_FILE_OFFSET_BITS=64: see man7.org/linux/man-pages/man7/feature_test_macros.7.html – Pringle

Answer 3

This code works for me in Linux:

int64_t bigFileSize(const char *path)
{
    struct stat64 S;

    if(-1 == stat64(path, &S))
    {
        printf("Error!\r\n");
        return -1;
    }

    return S.st_size;
}

Animate

Answer 4

(stolen from the glibc manual)

int fgetpos64 (FILE *stream, fpos64_t *position)

This function is similar to fgetpos but the file position is returned in a variable of type fpos64_t to which position points.

If the sources are compiled with _FILE_OFFSET_BITS == 64 on a 32 bits machine this function is available under the name fgetpos and so transparently replaces the old interface.

Penniepenniless

Answer 5

Stat is always better than fseek to determine file size, it will fail safely on things that aren't a file. 64 bit filesizes is an operating specific thing, on gcc you can put "64" on the end of the commands, or you can force it to make all the standard calls 64 by default. See your compiler manual for details.

Diploblastic

Answer 6

On linux, at least, you could use lseek64 instead of fseek.

Norvin