CODEWITHSUNDEEP
c++
Ivanp
Ivanp

Reputation: 455

No operator "==" maches these operands

so I try to compare iterator value that I get from it->second with int to get the key from map on the base of the value. I have this code :

std::map<string, std::vector<int> >::const_iterator it;
void getStudentByGrade(int gradeComp)
{
    for (it = studMap.begin(); it != studMap.end(); it++)
    {
        if (it->second == gradeComp)
        {
            cout << it->first;
        }
    }
}

and in the if statement I get the error , but I compare two ints don't I ?? The int that is passed as gradeComp and the it->second.

The error is:

Severity Code Description Project File Line Suppression State Error C2678 binary '==': no operator found which takes a left-hand operand of type 'const std::vector>' (or there is no acceptable conversion)

How to solve the error ? I found examples of getting to key with value only with iterator.

Upvotes: 2

Views: 159

Answers (1)

YSC
YSC

Reputation: 40060

I compare two ints don't I??

No you do not. Look:

it->second == gradeComp

Since it is an (const) iterator to std::map<string, std::vector<int>>, it->second has type std::vector<int> const&. On the other hand, gradeComp is an int. This is why your compiler tells you

No operator “==” maches these operands

those operands being a vector of integers and an integer.

How to solve the error?

Well, it depends on what you mean. Do you mean to search gradeComp in the vector? Or maybe you mean to compare it with a specific value from the vector?

// is gradeComp contained in the found vector?
if (end(it->second) != std::find(begin(it->second), end(it->second), gradeComp))
{ /* ... */ }

// does gradeComp match n-th value of vector?
if (gradeComp  == it->second[n])
{ /* ... */ }

Upvotes: 6

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