boost::variant linker error with gcc - c++

Question

I am going a bit nuts trying to figure out why the following won't compile:
#include <iostream>
#include <array>
#include <boost/variant.hpp>
#include <forward_list>
typedef unsigned long long very_long;
typedef boost::variant< int, std::string > variants_type;
typedef std::array< variants_type, 5 > row_type;
typedef std::forward_list<row_type> rows_holder_type;
int main() {
rows_holder_type rows;
row_type row_data;
row_data[0] = 0;
row_data[1] = 0;
row_data[2] = 0;
row_data[3] = 0;
row_data[4] = 0;
rows.push_front(row_data);
}
This is the compiler error I am getting:
/usr/include/testing/test_code.o||In function 'std::array<boost::variant<int, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>, 5ul>::array(std::array<boost::variant<int, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>, 5ul> const&)':|
store.cpp:(.text._ZNSt5arrayIN5boost7variantIiSsNS0_6detail7variant5void_ES4_S4_S4_S4_S4_S4_S4_S4_S4_S4_S4_S4_S4_S4_S4_S4_S4_EELm5EEC2ERKS6_[_ZNSt5arrayIN5boost7variantIiSsNS0_6detail7variant5void_ES4_S4_S4_S4_S4_S4_S4_S4_S4_S4_S4_S4_S4_S4_S4_S4_S4_EELm5EEC5ERKS6_]+0x31)||undefined reference to 'boost::variant<int, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_>::variant(boost::variant<int, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_, boost::detail::variant::void_> const&)'|
||=== Build finished: 1 errors, 0 warnings ===|
If I replace:
typedef boost::variant< int, std::string > variants_type;
with:
typedef boost::any variants_type;
The code compiles, but I do not want to use boost::any for performance reasons.

Answer 1

I tested your code with MSVC and gcc 4.7.0. MSVC compiles and links the code fine (of course with #include <string>), but gcc gives a linker error on the last line rows.push_front(row_data);. If you comment that line out, gcc accepts the code. I see no reason why gcc gives a linker error and am concluding that it is a bug with gcc. One workaround on gcc would be to change std::array to std::vector.
(From the error message I assume you are using Code::Blocks with gcc)
I've eliminated extra code and the following example still gives the linker error:
#include <boost/variant.hpp>
#include <array>
int main()
{
std::array<boost::variant<int, double>, 5> row_type1;
std::array<boost::variant<int, double>, 5> row_type2 = row_type1;
}

Answer 2

You're missing #include <string>; other than that your code is fine.