Simple program with a structure. Getting this: invalid operands of types 'void' and '<unresolved overloaded function type>' to binary 'operator

Question

I'm trying to call a void function that displays contents of a structure variable but I get this error when I call the function.

invalid operands of types 'void' and '<unresolved overloaded function type>' to binary 'operator

Honestly I am new to c++ and I don't understand what the error means. How do I fix this?

#include <iostream>

using namespace std;

struct MovieData
{
    string title;
    string director;
    int yearReleased;
    int runningTimeInMinutes;
};

void showMovieData(MovieData movie);

int main()
{
    MovieData apocalypseNow = {"Apocalypse Now", "Francis Ford Coppola", 1979, 153};
    MovieData theWizardOfOz = {"The Wizard of Oz", "Victor Fleming", 1939, 101};

    //error occurs here
    showMovieData(apocalypseNow) << endl;
    showMovieData(theWizardOfOz) << endl;

}


void showMovieData(MovieData movie)
{
    cout << "Title: " << movie.title << endl;
    cout << "Director: " << movie.director << endl;
    cout << "Year Released: " << movie.yearReleased << endl;
    cout << "Running Time (in minutes): " << movie.runningTimeInMinutes << endl;
}

Answer 1

Take a look at this code:

showMovieData(apocalypseNow) << endl;
showMovieData(theWizardOfOz) << endl;

Here, showMovieData is a function that returns void , meaning that it doesn't evaluate to a value. The code you've written is then trying to apply operator << to a nonexistent value and endl , which is impossible because you can't apply any operators to a void value.

To fix this, consider rewriting the code as

 showMovieData(apocalypseNow);
 cout << endl;
 showMovieData(theWizardOfOz);
 cout << endl;

Alternatively, replace showMovieData with a global operator<< operator that can be used to display objects of type MovieData , like this:

ostream& operator<<(ostream& out, const MovieData& movie)
{
    out << "Title: " << movie.title << endl;
    out << "Director: " << movie.director << endl;
    out << "Year Released: " << movie.yearReleased << endl;
    out << "Running Time (in minutes): " << movie.runningTimeInMinutes << endl;
    return out;
}

Then, you can write

cout << apocalypseNow << endl;
cout << theWizardOfOz << endl;

That said, the operator<< definition above isn't ideal because it inserts endl into the stream, flushing the contents, but it should also work. You may want to consider to replace endl inside operator<<(ostream&, const MovieData&) with '\\n' which avoids the flushing.

Hope this helps!

Answer 2

You can't call the function "showMovieData" in the same expression that you call the endl statement.

You should rewrite those two lines giving errors as:

showMovieData(apocalypseNow);
cout << endl;
showMovieData(theWizardOfOz);
cout << endl;

Edit - beaten to it, see answer below which is more thorough.