How to write data in >4GB file with C++?

Question

I\'m trying to write a large file, but ran into a problem.

I use long long for seeking a place to write, but can\'t write file more than 4,2Gb. What I forgot?

Mo

Answer 1

    fseeko64 (Filename, 0, SEEK_END);
    long size = ftello64 (Filename);
    fclose (Filename);

For accessing the large files , fseek cannot be used , instead have to go for fseeko64();

Answer 2

There is a nice summary for Linux here:

http://www.suse.de/~aj/linux_lfs.html

And more specific detail from RedHat targetting RHEL, these problems are generally for 32-bit applications accessing 64-bit sized files.

http://people.redhat.com/berrange/notes/largefile.html

Wikipedia actually has an artile on Large File Support but not really that informative.

Answer 3

There's a function called _lseeki64() on Win32, and lseek64() on *nix. The iostream library, however, does not wrap them directly, you'll have to retrieve the file descriptor somehow, and do something about buffering.

Answer 4

Many filesystems do not support files larger than 4GB. In addition, you should consider that your int type may have a range that ends at 2^32, i.e. 4.29497e+09.