Better way to determine length of a std::istream?

Question

Is there a better way to determine the length of an std::istream than the following:

std::istream* pcStream = GetSomeStream();
pcStream->seekg(0, ios::end);
unsigned int uiLength = pcStream->tellg();

It just seems really wasteful to have to seek to the end of the stream and then seek back to the original position, especially if the stream might be to a file on some slow media like a CD or DVD.

Answer 1

The "best" way is to avoid needing the length :)

• Not all streams are seekable (For example, imagine an istream on a network socket)
• The return type from tellg() is not necessarily numeric (the only requirement is that it can be passed back to seekg() to return to the same position)
• Even if it is numeric, it is not necessarily a number of bytes. For example, it could be a "magic" value meaning "at the end"
• For fstreams, issues like case and linefeed conversion can screw things up

Answer 2

Have you considered keeping track of the size by using istream::gcount() ?