Using C filestreams fstream how can you determine the size of a file

Question

I m sure I ve just missed this in the manual  but how do you determine the size of a file  in bytes  using C   s istream class from the fstream header

User · Answer

Like this   long begin  end  ifstream myfile   example txt    begin   myfile tellg    myfile seekg  0  ios  end   end   myfile tellg    myfile close    cout  lt  lt   size     lt  lt   end-begin   lt  lt    bytes    lt  lt  endl

User · Answer

Don t use tellg to determine the exact size of the file  The length determined by tellg will be larger than the number of characters can be read from the file   From stackoverflow question tellg   function give wrong size of file  tellg does not report the size of the file  nor the offset from the beginning in bytes  It reports a token value which can later be used to seek to the same place  and nothing more   It s not even guaranteed that you can convert the type to an integral type    For Windows  and most non-Unix systems   in text mode  there is no direct and immediate mapping between what tellg returns and the number of bytes you must read to get to that position   If it is important to know exactly how many bytes you can read  the only way of reliably doing so is by reading  You should be able to do this with something like    include  lt fstream gt   include  lt limits gt   ifstream file  file open name std  ios  in std  ios  binary   file ignore  std  numeric limits lt std  streamsize gt   max      std  streamsize length   file gcount    file clear          Since ignore will have set eof  file seekg  0  std  ios base  beg

User · Answer

I m a novice  but this is my self taught way of doing it   ifstream input file  example txt   ios  in   ios  binary   streambuf  buf ptr    input file rdbuf      pointer to the stream buffer  input get      extract one char from the stream  to activate the buffer input unget      put the character back to undo the get    size t file size   buf ptr- gt in avail      a value of 0 will be returned if the stream was not activated  per line 3

User · Answer

You can open the file using the ios  ate flag  and ios  binary flag   so the tellg   function will give you directly the file size   ifstream file   example txt   ios  binary   ios  ate   return file tellg

User · Answer

You can seek until the end  then compute the difference   std  streampos fileSize  const char  filePath         std  streampos fsize   0      std  ifstream file  filePath  std  ios  binary         fsize   file tellg        file seekg  0  std  ios  end        fsize   file tellg   - fsize      file close         return fsize

[c++] Using C++ filestreams (fstream), how can you determine the size of a file?

Examples related to c++

Examples related to filesize

Examples related to fstream

Examples related to istream