Unable good solution for set filter buffer size

Hello.

I want to make a filter for more beautiful text output. To do this, I need to collect a large amount of data, make beauty and output to std :: cout. Ideally, I should only process data when flush () is used;

I could not do it !!!

Here is an example.

`
#include

// I don't like this
//#define BOOST_IOSTREAMS_DEFAULT_FILTER_BUFFER_SIZE 1024

#include

struct toupper_filter
{
typedef char char_type;
typedef boost::iostreams::multichar_output_filter_tag category;

template
std::streamsize write(Sink& snk, const char* s, std::streamsize n)
{
// point to interest n=128. But i need more large (many kbs). Idealy i need to enter this only after flush()
std::streamsize rest = n;

for (; rest; --rest, s++)
{
int c = toupper(*s);

bool bOk = boost::iostreams::put(snk, c);

if (!bOk)
break;
}

return n - rest;
}
};

int main()
{
namespace io = boost::iostreams;

io::filtering_ostream out;

out.push(toupper_filter());
out.push(std::cout);

// This does not work!!!
out.set_filter_buffer_size(1024);

// dont use std::endl
for (size_t x = 0; x < 100; ++x)
{
out << "something\n";
out << "anything\n";
}

out.flush();

return 0;
}
`
out.set_filter_buffer_size(1024); - this not work!

Change BOOST_IOSTREAMS_DEFAULT_FILTER_BUFFER_SIZE is work, but it affected to all boost::iostream library. I think it is a bad idea.