hello,
to get started with iostreams, i'm trying to write a multichar output
filter that adds a string to the beginning and the end of whatever comes
through. my code builds with a warning about unused parameter n and
works - but only the first time, the second time, i get no output.
i thought at first sending '\0' would trigger the stream's fail-bit or
so, but out.good() returns true.
any chance someone takes a look at my code and hazards a guess where the
problem might be ?
disclaimer: i was actually born and bred in C++ country long time ago,
but i've been coding in python for a couple of years and got back only
recently, so there's a good chance what i'm doing wrong is something
really simple. guess you can tell from the code, it's been a while. good
to be back though... :-)
#include <iostream>
#include <sstream>
#include
#include
#include
using std::cin;
using std::cout;
using std::endl;
using std::streamsize;
using std::string;
using std::stringstream;
class add_string_output_filter
: public boost::iostreams::multichar_output_filter
{
public:
template<typename Sink>
streamsize write(Sink& sink, const char* s, streamsize n)
{
// remove trailing '\0' to prevent line break
// TODO: there's probably a better way
string tmp_string = string(s);
string out_string = tmp_string.substr(0, tmp_string.size()-1);
string pre_string("prepended string - ");
string app_string(" - appended string");
stringstream sstrm;
sstrm << pre_string << out_string << app_string << endl;
// TODO: char* to string, back to char* ?!?
return boost::iostreams::write(sink,
sstrm.str().c_str(),
sstrm.str().length());
}
};
int main()
{
boost::iostreams::filtering_ostream out;
out.push(add_string_output_filter());
out.push(cout);
cout << "prompt: ";
string str;
while (getline(cin, str))
{
out << str << endl;
cout << "prompt: ";
}
}
# sample session:
prompt: some string
prepended string - some string - appended string
prompt: another string
prompt: why no output ?
prompt:
# ssc
