C++ error: no match for 'operator<<'

Question

Hello I have a problem with this error I cannot understand what's the problem.. So here is full code:

#include <iostream>
#include <string>

using namespace std;

class GradeBook
{
public:
    GradeBook(string name)
    {
        setCourseName(name);
    } // end GradeBook constructor

    void setCourseName(string name)
    {
        courseName = name;
    } // end setCourseName

    string getCourseName()
    {
        return courseName; // return object's courseName
    } // end getCourseName

    void displayMessage()
    {
        cout << "Welcome to the grade book for\n" << getCourseName() << "!" << endl;
    } // end displayMessage
private:
    string courseName;
}; // end class GradeBook

int main()
{
    // create two GradeBook objects
    GradeBook gradeBook1("CS101 Introduction to C++ Programming");
    GradeBook gradeBook2("CS102 Data Structures in C++");

    cout << "gradeBook1 created for course: " << gradeBook1.displayMessage();
}

Error part is when I'm trying to print out this line:

cout << "gradeBook1 created for course: " << gradeBook1.displayMessage();

If I use it just like gradeBook1.displayMessage(); it prints the message but if I use it in like I showed it gives me nasty error..

Thanks!

`displayMessage` returns `void`. You can't stream that - it's nothing. — jrok, Feb 18 '14 at 12:25

herohuyongtao · Accepted Answer · 2014-02-18T12:32:54.870

2

displayMessage() is a function who returns void. You can't stream this as it's nothing. Just call it in separate lines.

Change

cout << "gradeBook1 created for course: " << gradeBook1.displayMessage();

to

cout << "gradeBook1 created for course: ";
gradeBook1.displayMessage();

edited Feb 18 '14 at 12:32

answered Feb 18 '14 at 12:25

herohuyongtao

49,413
29
133
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Well this works, thank you! But then I'm wondering why that kind of example which is not working is in book.. Thanks – Sangsom Feb 18 '14 at 12:28
2

I strongly recommend you to change the book! – Chethan N Feb 18 '14 at 12:30
@user2363241 Just change the book. :P – herohuyongtao Feb 18 '14 at 12:31
1

@user2363241 For books, look at this list: http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list – herohuyongtao Feb 18 '14 at 12:32
Okay thanks for answers and suggestions.. I'm going to look for new book.. Good luck ) – Sangsom Feb 18 '14 at 12:35

score 1 · Answer 2 · answered Feb 18 '14 at 12:28

1

It gets expanded to :

cout << { cout << "Welcome to the grade book for\n" << getCourseName() << "!" << endl } ; which is surely illogical .

So , use :

cout << "gradeBook1 created for course: "; gradeBook1.displayMessage();

answered Feb 18 '14 at 12:28

Aseem Goyal

2,683
3
31
48

score 1 · Answer 3 · answered Feb 18 '14 at 12:31

If you want to use << operator with class gradeBook1, overload the operator. Instead of using the displayMessage(); method in the class.

ostream &operator<<(ostream &out)
{
     out<<"Welcome to the grade book for\n" << getCourseName() << "!" << endl;
     return out;
}

The you can call your object using cout, as follows,

cout<<gradeBook1;

C++ error: no match for 'operator<<'

3 Answers3