The compiler will give the compile-time error: "invalid lvalue in unary '&'" The following code not only shows the bug, but also the non-template based implementation that runs and compiles perfectly. The two dimensional array is essential to observe the problem. The template code will run and compile perfectly when the 2d array is replaced by a 1d array. #include <iostream> #include <vector> /* const int data[2][4] = { {0, 1, 2, 3}, {4, 5, 6, 7} }; */ // For a one dimensional array the code compiles and runs in the policy based // case const int data[4] = { 4, 5, 6, 7 }; //This template implementation doesn't even compile due to some strange //compile-time error. //---------------- BEGIN TEMPLATE CODE --------------------------- template <typename T> class ExtremalInt { private: T extremal; public: ExtremalInt() : extremal(3) { } void operator()(int k) { int candidate = data[k]; if (extremal < candidate) { extremal = candidate; } } const int result() const { return extremal; } }; typedef ExtremalInt<int> MaxExtremalInt; //---------------- END TEMPLATE CODE --------------------------- /* //---------------- BEGIN EQUIVALENT CODE --------------------------- class MaxExtremalInt { private: int extremal; public: MaxExtremalInt() : extremal(3) { } void operator()(int k) { int candidate = data[1][k]; if (extremal < candidate) { extremal = candidate; } } const int result() const { return extremal; } }; //---------------- END EQUIVALENT CODE --------------------------- */ int main() { int result; std::vector<int> array; array.push_back(1); //5 array.push_back(3); //7 array.push_back(2); //6 MaxExtremalInt sMax; result = std::for_each(array.begin(), array.end(), sMax).result(); std::cout << "Result: " << result << "\n"; }
-- Summary: Misterious compiler error when accessing a 2d-array in a template class Product: gcc Version: 4.0.1 Status: UNCONFIRMED Severity: normal Priority: P2 Component: c++ AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: bdonner at physik dot tu-muenchen dot de CC: gcc-bugs at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23993