Question

I am used to writing codes using stl pair without including any specific header file for using pair. But a friend today told me that I should use utility header whenever I use pair else I will have problem on some compilers. Please tell if this is true. And what is the use of utility header if I can write codes without using it.

Answer 1

You should almost always include header file for every class which you use in your program, otherwise you depend on the fact that some headers internally use a class of your interest, but this can change on another compiler or version. You need to read reference of a class (for example on cppreference.com – http://en.cppreference.com/w/cpp/utility/pair ) and check which header file you need to include – in case of std::pair you should add #include <utility> . You cannot depend on the fact, that, for example, iostream already includes iomanip and your code compiles when you use manipulators like setw etc. You cannot – you always should refer to language specs and include required headers.