Re: Template-based code doesn't compile
late-enthusiast wrote:
#ifndef __TOTAL_H_
#define __TOTAL_H_
Your program is already ill-formed here. All identifiers containing two
consecutive underscores are reserved.
template<typename T> class Total
{
public:
Total<T>(const list<T>& l);
Make that
Total(const list<T>& l);
The first "<T>" is not required. Also consider adding "explicit" unless
you want implicit conversion.
~Total();
virtual T compute();
The object is both copyable and assignable, but this usually doesn't play
nice with inheritance, because you can't change the actual type of an
object through assignment. Also, you typically want a virtual destructor
in case of inheritance.
template<typename T> class Sum : public Total<T>
{
public:
Sum<T>(const list<T>& l) : figures(l) {}
Note: This will not(!) initialize the "Total<T>" base subobject with "l",
i.e. not call the constructor you declared above. IOW, its baseclass'
"figures" member will remain empty. Also note that having a member named
"figures" in both the baseclass and the derived class doesn't help
clarity.
Sum<double> *sum = new Sum(figures);
Average<double> *avg = new Average(figures);
[...]
sum.cpp: In function `int main(int, char**)':
sum.cpp:24: error: `Sum' is not a type
sum.cpp:25: error: `Average' is not a type
Two things here:
1. There is no reason to use "new" here. If you have a Java background,
forget about its use of "new" and relearn it the C++ way.
2. "Sum" and "Average" are not types, they are templates. The types you
want here are Sum<double> and Average<double>, which is what you must use
with "new" (apart from not using new in the first place).
This is the error I get when I run "gcc sum.cpp"
Two more things:
1. The C++ frontend is called g++ typically. I think gcc works, too,
because it autodetects the used language.
2. Always compile with warnings.
Uli
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