Compiler error message with cout

Question

I mistyped the error message before. It is fixed now.

I'm currently getting the following compiler error message

error: no match for 'operator<<' in 'std::cout << Collection::operator[](int)(j)'

The code that the compiler is complaining about is

cout << testingSet[j];

Where testingSet is an object of type Collection that has operator[] overloaded to return an object of type Example. Example has a friend function that overloads operator<< for ostream and Example.

note: this actually compiles just fine within Visual Studio; however does not compile using g++.

Here is the implementation of operator<<:

ostream& operator<<(ostream &strm, Example &ex)
{
     strm << endl << endl;
     strm << "{ ";
     map<string, string>::iterator attrib;
     for(attrib = ex.attributes.begin(); attrib != ex.attributes.end(); ++attrib)
     {
          strm << "(" << attrib->first << " = " << attrib->second << "), ";
     }
     return strm << "} classification = " << (ex.classification ? "true" : "false") << endl;
}

And the operator[]

Example Collection::operator[](int i)
{
      return examples[i];
}

Instead of describing what you think the implementation is - post the actual implementation. It obviously is not what you think it is. — oh whatever
– oh whatever, Commented Oct 3, 2011 at 9:14
Can you point us in the direction of the documentation for std::Collection? I've not come across this part of the C++ Standard Library before. — johnsyweb
– johnsyweb, Commented Oct 3, 2011 at 9:15
(also, I would try to get out of the habit of writing using namespace std and into the habit of writing std::ostream and std::cout). — Tom
– Tom, Commented Oct 3, 2011 at 9:20
So why on Earth is it qualified with std::? See stackoverflow.com/q/320798/78845 — johnsyweb
– johnsyweb, Commented Oct 3, 2011 at 9:21

rodrigo · Accepted Answer · 2011-10-03 09:27:46Z

6

Probably your operator should be declared as:

ostream& operator<<(ostream &strm, const Example &ex)

Note the const-reference to Example. Visual Studio has an extension that allows to bind a reference to a non-const r-value. My guess is that your operator[] returns an r-value.

Anyway, an operator<< should be const as it is not expected to modify the written object.

answered Oct 3, 2011 at 9:27

rodrigo

99.3k13 gold badges162 silver badges205 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Daniel Over a year ago

Yes, but then I cannot use iterators in the way that I have in my implementation. How could I fix that?

rodrigo Over a year ago

Using map<string, string>::const_iterator attrib;? You are not modifying the object, are you?

Daniel Over a year ago

Aha! That was it. I didn't know about the const_iterator. Thanks!

Daniel Over a year ago

Oh sorry, a jumped the gun a little bit. I'm actually still getting the error :(

Daniel Over a year ago

Ah, but now it is fixed. Making the operator[] return a const string was the final touch.

|

Collectives™ on Stack Overflow

Compiler error message with cout

1 Answer 1

6 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related