Cannot write more than 1023 bytes at once on shared drive via C++ ofstream => Fixed in SVN

[Dirk Farin]

I have a strange behaviour when writing files to shared folders on the host system. The configuration is: host: Windows-XP guest: Linux, Debian, 2.6.22 (lenny / testing) gcc on guest: 4.2.3

When using this simple test program, compiled on the guest linux system:

---

#include <iostream> #include <iomanip> #include <fstream>

int main(int argc, char *argv[]) {

char buf[5000];

for (int i=0;i<5000;i++) buf[i]=1;

std::ofstream os("out", std::ios::binary | std::ios::out); os.write(buf, 1024);

os << "end" << std::endl;

}

---

The program writes only 'zeros' instead of 'ones' when the output is a shared host folder (ntfs, mount options: "rw,exec,suid,dev"). This happens when the number of bytes written is >=1024. For chunks smaller than 1023, it works ok. It also works ok, if the output is on the guest file-system.

If the last line is removed (the file output is not flushed), no output is written at all (zero-length file). The ios::bad flag is not set after writing, claiming that everything went ok.

Replacing the ofstream output with fwrite-based code works ok for all sizes.

Not sure, if this is a stdc++ problem or a VirtualBox problem, but since the problem occurs with several gcc versions and only appears when writing to the host filesystem, it seems to be related to VirtualBox.

[Frank Mehnert]

Finally fixed in SVN. The fix will be available in the next release.