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C++ outputing to two streams together

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struct DoubleStream {
DoubleStream(ostream& a, ostream& b) : a_(a), b_(b) {
}
template<typename T>
DoubleStream& output(const T& object) {
a_ << object;
b_ << object;
return *this;
}
private:
ostream& a_;
ostream& b_;
};

template<typename T>
DoubleStream& operator<<(DoubleStream& ds, const T& object) {
return ds.output(object);
}


Usage

#include "DoubleStream.h"
#include <iostream>
#include <complex>

int main() {
DoubleStream ds = DoubleStream(std::cout, std::err);
ds << "Hello, World!" << ds << std::endl;
ds << 5.5 << std::endl;
ds << std::complex<double>(1.412, 16.5) << std::endl;
return 0;
}

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or even


class funcStreamer
{
funcStreamer(ostream &a, ostream &b)
: m_a(a), m_b(b) {}

template <typename DATA_TYPE>
void operator() (const DATA_TYPE& data)
{
m_a << data;
m_b << data;
}

private:
ostream &m_a;
ostream &m_b
}

// in use
ostream a, b;
funcStreamer outFunc(a, b);

outFunc("string value");


longer to write but shorter to use

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I thought I would be a little different and do something most likely not useful:


#include <utility> // std::pair
#include <iterator> // std::ostream_iterator, std::output_iterator_tag
#include <iosfwd> // std::char_traits

template < typename Tp, typename CharT = char, typename Traits = std::char_traits<CharT> >
struct pair_ostream_iterator
: std::pair< std::ostream_iterator<Tp, CharT, Traits>,
std::ostream_iterator<Tp, CharT, Traits> > {

typedef CharT char_type;
typedef Traits traits_type;
typedef std::basic_ostream<CharT, Traits> ostream_type;
typedef std::pair< first_type, second_type > pair_type;

typedef std::output_iterator_tag iterator_category;
typedef void value_type;
typedef void difference_type;
typedef void pointer;
typedef void reference;

typedef pair_ostream_iterator<Tp, CharT, Traits> Self;

pair_ostream_iterator(ostream_type& out1, ostream_type& out2, const CharT* Delim = 0)
: pair_type(first_type(out1, Delim), second_type(out2, Delim)) {}

Self& operator=(const Tp& val) {
first = val, second = val;
return *this;
}

Self& operator*() { // pretend to return designated value
return *this;
}

Self& operator++() { // pretend to preincrement
return *this;
}

Self operator++(int) { // pretend to postincrement
return *this;
}
};


example usage:


#include <cstddef> // std::size_t
#include <cmath> // std::rand
#include <algorithm> // std::generate_n, std::copy
#include <iterator> // std::back_inserter
#include <vector> // std::vector
#include <iostream> // std::cout, std::cerr

int main() {

const std::size_t N = 10;

std::vector<int> v;

v.reserve(N);
std::generate_n(std::back_inserter(v), N, std::rand);

std::copy(v.begin(), v.end(), pair_ostream_iterator<int>(std::cout, std::cerr, "\n"));
}


[Edited by - snk_kid on May 25, 2005 6:46:10 PM]

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thanks for that but
sorry i should of been more specific i want to be able to (*)chain them together
thus only petewood's suggestion is applicable
but i get the following error
ds << std::flush;
error C2678: binary '<<' : no operator defined which takes a left-hand operand of type 'struct DoubleStream'

(*)able to input multiple data in one line eg string << float << string << flush;

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