Why does the default argument not work in a template function?

Question

struct A {};

template<typename T>
void f(int n, T m = 3.14159)
{}

int main()
{    
    f(8, A{}); // ok
    f(8); // error: no matching function for call to 'f'
}

See online demo

Why does the default argument not work in a template function?

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EDIT: I also tried following, and wonder why it didn't work as well.

void g(int, auto = 3.14159)
{}

Answer 1

Default function arguments don't affect template argument deduction.

You need a default argument for the template parameter too: typename T = double.

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As for void g(int, auto = 3.14159), there seems to be no way to fix it.