Question

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Where and why do I have to put the “template” and “typename” keywords?

recently a piece of code confused me:

class A {
 public:
  typedef int SomeType;

  void func(SomeType i);
  SomeType func2();
};

void A::func(SomeType i) {
  cout << "in A, value: " << i << endl;
}
SomeType A::func2() {
  return 123;
}

int main() {
  A a;
}

G++ 4.4 gives a compile error that it does not know the SomeType while compiling A::func2:

error: 'SomeType' does not name a type

But the same SomeType compiles well in A::func(SomeType i):

class A {
 public:
  typedef int SomeType;

  void func(SomeType i);
};

void A::func(SomeType i) {
  cout << "in A, value: " << i << endl;
}

Anyone can help me to understand this? It seems C++ treats unfair to argument types and return types?

Answer 1

gcc is right –

/* can't use unqualified name */  A:: /* can use unqualified name */  () {
}

Before the A::, you need to qualify the nested type with A::. So you need:

A::SomeType A::func2() {  
   //whatever
}