CODEWITHSUNDEEP
c++compilationcompiler-errorsstdio
Daniel
Daniel

Reputation: 6745

Compiler error message with cout

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];
}

Upvotes: 0

Views: 1228

Answers (1)

rodrigo
rodrigo

Reputation: 98338

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.

Upvotes: 6

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