c++ - Default constructing template parameters to zero if numeric? -

consider example:

template<typename t> auto f(t u, t v = t()) { return v; } int main() {     double a; float b; int c; long d;   // possible numerical types here     auto res1 = f(a);   // res1 == 0.0?     auto res2 = f(b);   // res2 == 0.0?     auto res3 = f(c);   // res3 == 0?     auto res4 = f(d);   // res4 == 0? } 

is there guarantee standard t() default construct 0 numerical value whenever t numerical type? if not, how can make sure if t numerical, default argument 'v' v = 0, , if t not numerical, v = t()?