c++11 - c++ auto with overriding signed/unsigned -

in following code:

#include <armadillo>  using namespace arma;  int main() {     mat a;     auto x=a.n_rows-5;     .... 

x long long unsigned int , want long long int. how can fix problem?

it should noticed on different versions of library, different types have been used, cannot mention long long int directly , need use auto.

you can use c++11 type traits library signed or unsigned version of numeric type.

to unsigned int:

std::make_unsigned<int>::type 

so signed version of a.n_rows, try:

std::make_signed<decltype(a.n_rows)>::type x = a.n_rows - 5; 

for other qualifiers, there corresponding templates convert between types:

• reference types - http://en.cppreference.com/w/cpp/utility/functional/ref
• pointer types - http://en.cppreference.com/w/cpp/types/add_pointer
• etc. (add or remove const, or volatile qualifiers)