syntax for declaring a function template

Question

I'm trying to create a template function that takes a vector argument of any type T (primitive for now) and prints out its contents:

template<class T>
void displayContents(const vector<T>& data)
{
    vector<T>::const_iterator i;
    i=data.begin();

    for( ; i!=data.end(); i++){
        cout<<*i<endl;
    }
}

The error message is:

In function 'void displayContents(const std::vector >&)': error: expected ';' before 'i' | error:'i' was not declared in this scope === Build finished: 2 errors, 0 warnings ===

Am I overlooking a syntax error?

Krizz · Accepted Answer · 2011-12-12T11:25:09.060

5

Try the following:

  typename vector<T>::const_iterator i;

As pointed out by Björn in the comment already, it is needed because is a dependent name of the template.

edited Dec 12 '11 at 11:25

answered Dec 12 '11 at 08:20

Krizz

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7

The problem is that `const_iterator` is a *dependent name* - you can read more about it here: http://stackoverflow.com/questions/610245. – Björn Pollex Dec 12 '11 at 08:27
"**the** dependent name of the template" is very misleading, `const_iterator` is **a** dependent name. – Sebastian Mach Dec 12 '11 at 10:40

score 3 · Answer 2 · answered Dec 12 '11 at 09:12

If your goal is to output every element, you shouldn't constrain yourself to vectors. The idiomatic, generic solution is to pass two iterators instead:

template<typename ForwardIterator>
void display_contents(ForwardIterator begin, ForwardIterator end)
{
    for (ForwardIterator it = begin; it != end; ++it)
    {
        std::cout << *it << '\n';
    }
}

Then you can use the template with vectors, sets and practically all other containers:

int main()
{
    std::vector<int> a {2, 3, 5, 7};
    display_contents(a.begin(), a.end());

    std::set<int> b {11, 13, 17, 19};
    display_contents(b.begin(), b.end());
}

Not exactly what I was looking for, but noted for future endeavours :) — Zubizaretta, Dec 14 '11 at 16:33

syntax for declaring a function template

2 Answers2