error: 'invalid operands' to binary operator <<

Question

I'm getting the following error:
invalid operands of types 'char' and unresolved overloaded function type>' to binary 'operator<<'

What does it mean?

#include <string>
#include <fstream>
using namespace std;

int main()
{
    ifstream inFile;
    inFile.open("records.txt");

    ofstream outFile;
    outFile.open("corrected.txt");

    while (inFile.good())
    {
        string num, temp;
        inFile >> num;
        outFile << temp.at(0)=num.at(9) << temp.at(1)=num.at(8) 
                << temp.at(2)=num.at(7) << temp.at(3)=num.at(6) 
                << temp.at(4)=num.at(5) << temp.at(5)=num.at(4) 
                << temp.at(6)=num.at(3) << temp.at(7)=num.at(2) 
                << temp.at(8)=num.at(1) << temp.at(9)=num.at(0) << endl; 
    // invalid operands of types 'char' and unresolved overloaded function type>'
    // to binary 'operator<<'
    }
    return 0;
}

This program is supposed to reverse back a list of phone numbers that have been reversed.

FYI, you can get a similar error (the types will be different) if you write the operator wrong, for example `<` instead of `<<`. Not the case here, but it may help others. — Dennis, Jun 09 '13 at 06:05

score 5 · Answer 1 · answered Mar 05 '12 at 02:33

You need to parenthesize your expressions or the wrong precedence breaks the code.

Replace temp.at(0)=num.at(9) with (temp.at(0)=num.at(9)), and so on. Then it will compile.

    outFile << (temp.at(0)=num.at(9)) << (temp.at(1)=num.at(8))
            << (temp.at(2)=num.at(7)) << (temp.at(3)=num.at(6))
            << (temp.at(4)=num.at(5)) << (temp.at(5)=num.at(4))
            << (temp.at(6)=num.at(3)) << (temp.at(7)=num.at(2))
            << (temp.at(8)=num.at(1)) << (temp.at(9)=num.at(0)) << endl;

error: 'invalid operands' to binary operator <<

1 Answers1