syntax of initializer_list for a vector of integers

Question

In order to understand how to use initializer_list, I'm writing a constructor of my own to fill a vector of integers (explanations here) :

#include <vector>

class X
{
  std::vector< int > *vec;
public:
  X(std::initializer_list<int>);
};

X(std::initializer_list<int> values)
{
  this->vec = new std::vector<int>(values);
}

The line

X(std::initializer_list<int> values)

is rejected by my g++ -std=c++11 : invalid declarator before values. Why ?

@πάντα ῥεῖ : you're right; of course, it was only an example. — suizokukan, May 25 '14 at 13:45
@hellfire769 Adding an existing tag to the title is an inappropriate edit! — πάντα ῥεῖ, May 25 '14 at 14:17
@πάντα ῥεῖ I didn't add the tag in the title, it was suizokukan — Daniel Heilper, May 25 '14 at 14:24
@hellfire769 Ah, sorry! I see you actually added the tag. Good edit action yes! — πάντα ῥεῖ, May 25 '14 at 14:27
@πάντα ῥεῖ I would have removed the C++ tag (too broad audience), but that is a subjective opinion... — Daniel Heilper, May 25 '14 at 14:29

score 5 · Answer 1 · answered May 25 '14 at 13:46

5

As Bo Persson noticed :

X(std::initializer_list<int> values)

must be written

X::X(std::initializer_list<int> values)

answered May 25 '14 at 13:46

suizokukan

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score 1 · Accepted Answer · answered May 25 '14 at 18:53

As you've discovered, when you define member functions, including special member functions, outside the class definition, you must use the fully qualified name. This is necessary to indicate the function you're declaring is a member of that class, and not a free function. There are a couple of other things you should fix about your class definition.

class X
{
  std::vector< int > vec;
  //                ^^^     - it's unlikely this needs to be a pointer
public:
  X(std::initializer_list<int>);
};

X::X(std::initializer_list<int> values)
//^^^             - fully qualified name required
: vec(values)  // use the constructor initializer list 
               // instead of assignment within the body
{
}

Thank you for all these details, specially for the ": vec(values)" syntax I didn't know. — suizokukan, May 25 '14 at 20:30
@suizokukan For reference, here's the [C++ FAQ](http://www.parashift.com/c++-faq-lite/init-lists.html) on why one should prefer using the constructor initializer list. — Praetorian, May 25 '14 at 21:07

syntax of initializer_list for a vector of integers

2 Answers2