boost::format gives error on overloaded << operator

wangkhem (4)
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#include <iostream>
#include <vector>
#include <boost/format.hpp>

namespace {
	struct X {
		int a;
		int b;
	};

	std::ostream &
	operator << (std::ostream &out, const std::vector<X> &x)
	{
		for (int i = 0; i < x.size(); ++i) {
			out << x[i].a;
			out << x[i].b;
		}
		return out;
	}

	std::ostream &
	operator << (std::ostream &out, const std::vector<int> &x)
	{
		for (int i = 0; i < x.size(); ++i) {
			out << x[i];
		}
		return out;
	}
}

int main()
{
	std::vector<X> x;
	X abc;
	abc.a = 5;
	abc.b = 6;
	x.push_back(abc);

	std::cout << x << std::endl;
	std::cout << (boost::format("%s") % x).str() << std::endl;


	std::vector<int> y;
	y.push_back(8);
	y.push_back(9);

	std::cout << y << std::endl;
	std::cout << (boost::format("%s") % y).str() << std::endl;
}


Can anyone please explain me why I am getting error only at the last std::cout. Looks like it happens on for build-in data type (int here), but not able to figure out why?
helios (17607)
What's the error?
wangkhem (4)
Commenting the last line will take out the below error



/usr/include/boost/format/feed_args.hpp: In function ‘void boost::io::detail::put_last(std::basic_ostream<_CharT, _Traits>&, T&) [with Ch = char, Tr = std::char_traits<char>, T = std::vector<int, std::allocator<int> >]’:
/usr/include/boost/format/feed_args.hpp:150:   instantiated from ‘void boost::io::detail::put(T, const boost::io::detail::format_item<Ch, Tr, Alloc>&, typename boost::basic_format<Ch, Tr, Alloc>::string_type&, typename boost::basic_format<Ch, Tr, Alloc>::internal_streambuf_t&, boost::io::detail::locale_t*) [with Ch = char, Tr = std::char_traits<char>, Alloc = std::allocator<char>, T = std::vector<int, std::allocator<int> >&]’
/usr/include/boost/format/feed_args.hpp:241:   instantiated from ‘void boost::io::detail::distribute(boost::basic_format<Ch, Tr, Alloc>&, T) [with Ch = char, Tr = std::char_traits<char>, Alloc = std::allocator<char>, T = std::vector<int, std::allocator<int> >&]’
/usr/include/boost/format/feed_args.hpp:251:   instantiated from ‘boost::basic_format<Ch, Tr, Alloc>& boost::io::detail::feed(boost::basic_format<Ch, Tr, Alloc>&, T) [with Ch = char, Tr = std::char_traits<char>, Alloc = std::allocator<char>, T = std::vector<int, std::allocator<int> >&]’
/usr/include/boost/format/format_class.hpp:68:   instantiated from ‘boost::basic_format<Ch, Tr, Alloc>& boost::basic_format<Ch, Tr, Alloc>::operator%(T&) [with T = std::vector<int, std::allocator<int> >, Ch = char, Tr = std::char_traits<char>, Alloc = std::allocator<char>]’
3.cpp:48:   instantiated from here
/usr/include/boost/format/feed_args.hpp:113: error: no match for ‘operator<<’ in ‘os << x’
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:67: note: candidates are: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>& (*)(std::basic_ostream<_CharT, _Traits>&)) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:78: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ios<_CharT, _Traits>& (*)(std::basic_ios<_CharT, _Traits>&)) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:90: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:241: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:264: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:102: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:125: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:157: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:183: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:215: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:288: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:311: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:361: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:335: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:384: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:407: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/ostream.tcc:430: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_streambuf<_CharT, _Traits>*) [with _CharT = char, _Trait
coder777 (8450)
Yes you have to #include <string> which brings the appropriate operator<<.

But format already has the appropriate operator<<:

This
std::cout << boost::format("%s") % y << std::endl;
is supposed to work (the operator% is due to this.
helios (17607)
You're including the headers before declaring the operator<<() overloads, which means the classes in those headers won't be able to see them.

By the way, the format string for boost::format should be "%1%", not "%s".
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