.compare not matching a string pulled from an object

I am trying to go threw a vector of Student objects. If I find a matching ID to the one I am searching for it will display their info.

However, when I try to find a specific ID .compare isn't seeing a match even though it should.

My output: first line is the ID I am looking for, second is the current ID being looked at, then is the result of the compare.

a11111111
a22222222
-1
no match

a11111111
a11111111
-1
no match

The code being run at this point:

void displayID(vector<Student>& vStu, string ID) {
    int count = vStu.size();
    string test;
    ID = "a11111111";


    for (int i = 0; i<count;i++) {
        cout<< endl;

        test = vStu[i].getId();
        cout << ID << endl;
        cout << test << endl;
        cout << ID.compare(test) << endl;

        if (ID.compare(test) == 0) {
            cout << "match" << endl;
            cout << vStu[i].getId() << endl;
            cout << vStu[i].getName() << endl;
            vStu[i].getGrades();
            cout << endl;
        } else {
            cout << "no match" << endl;
        }
    }   
    cout << endl;
}

Incase it will help, my student class:

class Student {
    public:
        void display(ostream& os) const;
        void setId(string);
        void setName(string, string);
        void setGrades(string, int);
        string getId();
        string getName();
        void getGrades();
        bool operator<(const Student &rhs) const { return id_ < rhs.id_;}
    private:
        string id_; // e.g. "a22222222"
        Name name_; // e.g. {"ned", "flanders"}
        Grades grades_;
};

string Student::getId() {
    return id_;
}