CODEWITHSUNDEEP
c++iooverloadingistream
bandera
bandera

Reputation: 49

overloading operator i/o probblem

I am trying to overload operator >> but I have a big error when I try to compile

std::istream& operator>>(std::istream & is)
{
string str;
is>>str;
vector<Cord> v;
cout<<str<<endl;
bool test=testeur(str, v);
if (test)
{
  for (unsigned int i=0;i<v.size();i++)
    table.push_back(v[i]);
}
return is;
}

my main:

istringstream tmp2 ( "(0,0) > (0,1)" );
tmp2 >> x1;

I get this error: test.cpp:473:9: error: no match for ‘operator>>’ in ‘tmp2 >> x1’ test.cpp:473:9: note: candidates are:

now I tried this:

    friend std::istream& operator>>(std::istream & is, const CGPS & rhs)
{
string str;
is>>str;
vector<CCoord> v;
cout<<str<<endl;
bool test=testeur(str, v);
if (test)
{
  for (unsigned int i=0;i<v.size();i++)
    rhs. Add (v[i]);
}
return is;
}

and I get this error:

test.cpp: In function ‘std::istream& operator>>(std::istream&, const CGPS&)’: test.cpp:448:29: error: cannot call member function ‘bool CGPS::testeur(std::string, std::vector&)’ without object test.cpp:452:23: error: no matching function for call to ‘CGPS::Add(CCoord&) const’ test.cpp:452:23: note: candidate is: test.cpp:106:12: note: CGPS& CGPS::Add(CCoord) test.cpp:106:12: note: no known conversion for implicit ‘this’ parameter from ‘const CGPS*’ to ‘CGPS*’

Upvotes: 0

Views: 303

Answers (2)

Dale Wilson
Dale Wilson

Reputation: 9434

The operator >> function cannot be a member function of the class because the first argument must be the istream rather than this.

Try this:

friend std::istream& operator>>(std::istream & is, MyClass & rhs)
{
    input the data here (you have access to private data)
    return is;
}

or if you only need public members of MyClass to access the data you need, you can make it a stand-alone free function in the same namespace. The declaration would look the same without the "friend". It should appear outside the declaration of the class, and you probably need to make it inline.

Clarification: You have (at least) three choices:

  • Declare (and define) the function as a friend function. It is not a class member even though the definition appears inside the class declaration.
    • With this choice you have access to private data in the class.
  • Declare (and define) the function as an inline function in the same header file as the class(and in the same namespace), but outside the class declaration, and use only public methods on the class to set the values read.
  • Declare the function in the same header file as the class. Define the body of the function in the cpp file. The difference is that the function is not inline.

For all of these choices, the operator >> function is stand-alone, not a member of the class.

Upvotes: 0

molbdnilo
molbdnilo

Reputation: 66371

The >> operator has to be a free function, since it's left hand side is the stream.

So you need to implement

std::istream& operator>>(std::istream& is, YourClass& x);

The syntax for calling your implementation would be

x1 >> tmp2;

which looks really strange.

Addendum:

You made two errors in your updated code:

  1. The CGPS parameter can't be const (it's the object you're reading into, so you'll be modifying it).
  2. testeur is apparently a member function of CGPS, so you should call it like rhs.testeur(str,v).

Upvotes: 1

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