C++ cout with prefix

Question

I want a ostream with a prefix at the beginning of every line redirected on cout; I try this:

#include 
#include 
class paralle         


        

Answer 1

As Dietmar said, what you want is your own streambuf, something on this general order:

#include 
#include 

class prefixer: public std::streambuf {
public:
    prefixer(std::streambuf* s): sbuf(s) {}
    ~prefixer() { overflow('\n'); }
private:
    typedef std::basic_string string;

    int_type overflow(int_type c) {

        if (traits_type::eq_int_type(traits_type::eof(), c))
            return traits_type::not_eof(c);
        switch (c) {
        case '\n':
        case '\r':  {
            prefix = "[FIX]";
            buffer += c;
            if (buffer.size() > 1)
                sbuf->sputn(prefix.c_str(), prefix.size());
            int_type rc = sbuf->sputn(buffer.c_str(), buffer.size());
            buffer.clear();
            return rc;
        }
        default:
            buffer += c;
            return c;
        }
    }

    std::string prefix;
    std::streambuf* sbuf;
    string buffer;
};

To use this, you create an instance of it from some other streambuf (that defines where it's going to write to) and then (usually) create an ostream using this streambuf. Then you can write to that ostream, and your prefix gets written to each line of output. For example:

int main() { 
    prefixer buf(std::cout.rdbuf());

    std::ostream out(&buf);

    out << "Test\n";
}