This is the code: ---Headers.h------ Code: #ifndef HEADERS_H #define HEADERS_H #include #include #include using namespace std; class data { private: // vector v; // string s1; public: data(); void Load_Price_Data(string); }; #include "Inlines.inl" #endif ------Inlines.inl---------- Code: data::data() { // couts1; } ---------Main.cpp Code: #include "Headers.h" int main() { system("pause"); return 0; } The kind of errors I get are: Code: error C2653: 'data' : is not a class or namespace name This error corresponds to reference to data::data() in file Inlines.inl When I move the data:data() call back into Headers.h, the program compiles file.