Compile this test program with "cc":

---cut here---
#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>

main()
{
  int real_position = lseek(fileno(stdin), 0, SEEK_CUR);
  int stdio_position = ftell(stdin);

  printf("really = %d, stdio = %d\n", real_position, stdio_position);
}
---cut here---

Then run "(cat >/dev/null; ./a.out) < foo", where "foo" is any non-empty
file.  It will print two identical numbers for "really" and "identical".

Now compile the same test program, this time using "c++" instead of "cc". 
This time, when you run the same test command, the "stdio" number will be 0
instead of matching the "really" number.

In short, ftell() in libstdc++ is not doing the right thing if the file
descriptor is at a non-zero position before stdio gets its hands on it.

This has real ramifications.  For one thing, it broke ghostscript (see bug
52505, which I just filed about this).