请教一个二元谓词问题...........

C/C++ code

#include <set>#include <string>#include <iostream>using namespace std;enum MenuOptionSelection{    InsertContactsetEntry = 0,    DisplayEntries = 1,    FindNumber = 2,    EraseEntry = 3,    FindName = 4,    QuitApplication = 5};struct ContactItem{    string strContactsName;    string strPhoneNumber;    ContactItem(const string &strName,const string &strNumber)    {        strContactsName = strName;        strPhoneNumber = strNumber;    }    bool operator== (const ContactItem &itemToCompare) const    {        return (itemToCompare.strContactsName == this->strContactsName);    }    bool operator< (const ContactItem &itemToCompare) const    {        return (this->strContactsName < itemToCompare.strContactsName);    }};struct FindContactGivenNumber{    bool operator() (const ContactItem &item1,const ContactItem &item2) const    {        return (item1.strPhoneNumber < item2.strPhoneNumber);    }};int ShowMenu(){    cout<<"***What would you like to do next?***"<<endl<<endl;    cout<<"======================================="<<endl;    cout<<"Enter 0 to feed a name and phone number"<<endl;    cout<<"Enter 1 to Display all entries"<<endl;    cout<<"Enter 2 to find an entry"<<endl;    cout<<"Enter 3 to erase an entry"<<endl;    cout<<"Enter 4 to find name with phone number"<<endl;    cout<<"Enter 5 to quit this application"<<endl;    cout<<"======================================="<<endl<<endl;    cout<<"> ";        int nOptionSelected;    cin>>nOptionSelected;    cout<<endl;    return nOptionSelected;}ContactItem GetContactInfo(){    cout<<"***Feed contact information***"<<endl;    string strName;    cout<<"Please enter the person's name"<<endl;    cout<<"> ";    cin>>strName;    string strPhoneNumber;    cout<<"Please enter "<<strName<<"'s phone number"<<endl;    cout<<"> ";    cin>>strPhoneNumber;    return ContactItem(strName,strPhoneNumber);}void DisplayContactset(const set<ContactItem> &setContacts){    cout<<"***Displaying contact information***"<<endl;    cout<<"There are "<<setContacts.size()<<" entries:"<<endl;    set<ContactItem>::const_iterator iContact;    for (iContact = setContacts.begin()        ;iContact != setContacts.end()        ;++iContact)    {        cout<<"Name: '"<<iContact->strContactsName;        cout<<"' Number: '"<<iContact->strPhoneNumber<<"'";        cout<<endl;    }    cout<<endl;}void FindContactNumber(const set<ContactItem> &setContacts){    cout<<"***Find a contact***"<<endl;    cout<<"Whose number do you wish to find?"<<endl;    cout<<"> ";    string strName;    cin>>strName;    set<ContactItem>::const_iterator iContactFound = setContacts.find(ContactItem(strName,""));    if (iContactFound != setContacts.end())    {        cout<<strName<<" is reachable at number: ";        cout<<iContactFound->strPhoneNumber<<endl;    }     else     {        cout<<strName<<" was not found in the contacts list"<<endl;    }    cout<<endl;}void FindContactName(const set<ContactItem> &setContacts){    cout<<"***Find a contact***"<<endl;    cout<<"Whose name do you wish to find?"<<endl;    cout<<"> ";    string strNumber;    cin>>strNumber;    set<ContactItem>::const_iterator iContactFound = setContacts.find(ContactItem("",strNumber));    if (iContactFound != setContacts.end())    {        cout<<strNumber<<" is reachable at number: ";        cout<<iContactFound->strContactsName<<endl;    }     else     {        cout<<strNumber<<" was not found in the contacts list"<<endl;    }    cout<<endl;}void EraseContact(set<ContactItem> &setContacts){    cout<<"***Erase a contact***"<<endl;    cout<<"Whose number do you wish to erase?"<<endl;    cout<<"> ";    string strName;    cin>>strName;    size_t nErased = setContacts.erase(ContactItem(strName,""));    if (nErased > 0)                                                        cout<<strName<<"'s contact information erased."<<endl;    else        cout<<strName<<" was not found!"<<endl;    cout<<endl;}int main(){    set<ContactItem> setContacts;    int nUserSelection;    string strInput;    while ((nUserSelection = ShowMenu()) != (int)QuitApplication)    {        switch (nUserSelection)        {        case InsertContactsetEntry:            setContacts.insert(GetContactInfo());            cout<<"Contacts set updated!"<<endl<<endl;            break;        case DisplayEntries:            DisplayContactset(setContacts);            break;        case FindNumber:            FindContactNumber(setContacts);            break;        case EraseEntry:            EraseContact(setContacts);            DisplayContactset(setContacts);            break;        case FindName:            FindContactName(setContacts);            break;        case QuitApplication:            break;        default:            cout<<"Invalid input '"<<nUserSelection;            cout<<"'. Please choose an option between 0 and 4"<<endl<<endl;            break;        }    }    cout<<"Quiting! Bye!"<<endl<<endl;        char response;    cin>>response;    return 0;} 
 

这是一个作业:
在不修改ContactItem的情况下,扩展本章中的电话薄应用程序使其能够根据电话号码查找人名
书上给了一个提示:定义set时指定一个二元谓词.而这个二元谓词就是struct FindContactGivenNumber部分

其中,FindContactName()函数是我自己添加的,目的是通过这个函数输入号码找到人名

最开始我只添加了FindContactName()函数,我存入了正确的电话号码和人名 输入正确的号码却始终提示不在列表中
这个问题我不知道怎么解释,为什么存进去了缺找不到

第二个问题就是这个二元谓词到底怎样使用,我试过很多方法 ,编译器全部都报错 我想我肯定没加对

[解决办法]
在这个函数中void FindContactName(const set<ContactItem> &setContacts)，
下面这一个语句有错：
set<ContactItem>::const_iterator iContactFound = setContacts.find(Contac tItem("",strNumber));
set容器中查找的是ContactItem 对象的整体，而不是只查strNumber这一个变量