C++ error: default template arguments may not be used in function template

Question

I am trying to understand what the value = T() means and how to fix it. Also the function is a constructor for a class.

template<typename T>
Accumulator<T>::Accumulator(const T& value = T())
{
     total = value;
}

This does not compile the following errors are:

error: default argument given for parameter 1 of `Accumulator<T>::Accumulator(const T&)'
error: after previous specification in `Accumulator<T>::Accumulator(const T&)'

Basically the function is a constructor for a class with a default argument that sets "total" a private variable of my class to "value" if given a value for an argument.

Looks like the original function declaration (in the class) didn't have the default argument. — Niall, Oct 18 '14 at 19:43
`= T()` should be *only* a part of declaration if it is not an in-class definition — Piotr Skotnicki, Oct 18 '14 at 19:45
It is in a cpp file and I am not suppose to change the header file. — John, Oct 18 '14 at 19:51
templates must be entirely in header file unless you are using explicit instantiation — Piotr Skotnicki, Oct 18 '14 at 19:52
I am suppose to define this function in a separate file, the function I posted above was copied and pasted from the header file. — John, Oct 18 '14 at 19:58
@John why are you *supposed to define this function in separate file* ? — Piotr Skotnicki, Oct 18 '14 at 20:03

score 3 · Accepted Answer · answered Oct 18 '14 at 19:50

3

You should only specify the default parameter in the function declaration, in the header.

answered Oct 18 '14 at 19:50

Laura Maftei

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Okay I think i understand what you mean. The default arguments should be assigned in the earliest occurrence of a function definition. So removing the '= T()' should fix it but I get link errors now. – John Oct 18 '14 at 20:45
Yes, that's what i meant. – Laura Maftei Oct 19 '14 at 06:32

C++ error: default template arguments may not be used in function template

1 Answers1