c++ - How can I find out how many bytes are available from a std::istream? -

c++ - How can I find out how many bytes are available from a std::istream? -

if wanted read() content of std::istream in buffer, have find out how much info available first know how big create buffer. , number of available bytes istream, doing this:

std::streamsize available( std::istream &is ) { std::streampos pos = is.tellg(); is.seekg( 0, std::ios::end ); std::streamsize len = is.tellg() - pos; is.seekg( pos ); homecoming len; }

and similarly, since std::istream::eof() isn't useful fundtion afaict, find out if istream's pointer @ end of stream, i'm doing this:

bool at_eof( std::istream &is ) { homecoming available( ) == 0; }

my question:

is there improve way of getting number of available bytes istream? if not in standard library, in boost, perhaps?

for std::cin don't need worry buffering because buffered --- , can't predict how many keys user strokes.

for opened binary std::ifstream, buffered, can phone call seekg(0, std::ios:end) , tellg() methods determine, how many bytes there.

you can phone call gcount() method after reading:

char buffer[size]; while (in.read(buffer,size)) { std::streamsize num = in.gcount(); // phone call api num bytes in buffer }

for text input reading via std::getline(inputstream, a_string) , analyzing string afterwards can useful.

c++ boost stl istream