gcount, tellg, seekg functions

[ferdymercury]

tellg(), gcount() and seekg() functions might be helpful for estimating file size.

See https://stackoverflow.com/questions/2409504/using-c-filestreams-fstream-how-can-you-determine-the-size-of-a-file

[ferdymercury]

tellg

[sandsmark]

I think tellg works in general now, I needed it for debugging some file format issues so I tried to fix it:

81db815#diff-f957a3c12ea388ffadfa08b526d7ae5c52ce99fa70fce25fe583fbbadb27a624 (which is ironically the one that broke the test).

[ferdymercury]

instead of seekg to ios::end (or ios::ate) and tellg, an alternative way of getting the filesize would be:
https://en.cppreference.com/w/cpp/filesystem/file_size

For the 'uncompressed' file size, it could be:
std::distance(std::istreambuf_iterator<char>(file), std::istreambuf_iterator<char>());

[LuNoX]

@ferdymercury is there a reason the inherited gcount() wouldnt work?
As for seekg how would you want it to work? Should it decompress until it reaches the desired position?

[ferdymercury]

@ferdymercury is there a reason the inherited gcount() wouldnt work? As for seekg how would you want it to work? Should it decompress until it reaches the desired position?

I was thinking of a function GetFileSize:

    file.seekg(0, std::ios_base::beg);
    file.ignore(std::numeric_limits<std::streamsize>::max());
    std::streamsize length = file.gcount();
    file.clear(); //  Since ignore will have set eof.
    file.seekg(0, std::ios_base::beg);
    return length;

So maybe an extra gcount(bool decompress = false) function could be defined to tell you the uncompressed file size if you set decompress to true or sth like that, or default otherwise to the inherited function.