如何搜索列表元素，STL C ++

Question

I havd a problem with my code. I have class named CPerson.

class CPerson {
private:
    string name;
    string lastName;
    int age;
    char *pPesel;

public:

    CPerson( string i, string n, int w,   char *pPes);
...
};

I have a list.

list <CPerson> lst;

list <CPerson> ::iterator it;
it = lst.begin(); 

CPerson wzor1("John", "Steward", 22, "2323"  );

When i fill it up, i want find an CPerson instance whose lastName field begins, for example, with "Kow".

Is it possible to make that "Kow" as a parameter to the any function?

I was trying with find or find_if but it never worked, dont know how to write a predicate, any ideas?

Answer 1

A predicate is like a call back function on each element while iterating over the container.

bool VerifyLastName( CPerson& obj )
{
    return (obj.getLastName() == "Kow");
}

std::list<CPerson>::iterator it = std::find_if(lst.begin(), lst.end(), VerifyLastName);

If it is not equal to the lst.end() , then iterator is pointing to the object with the member whose last name is "Kow".

Answer 2

//Create a member function getLastName in your class
std::string CPerson::getLastName( void ){
return lastname;
}

//Create a function object for find_if use.
struct checkLastName{
    checkLastName(const std::string & test):checkName(test){}
    bool operator()( CPerson& ob ){
        return ob.getLastName().substr(0, checkName.size()).compare(checkName);
    }
    std::string checkName;
};

std::string lname;
cin>>lname; //"Kow"

//Use std::find_if
std::list<CPerson>::iterator it = 
             std::find_if(lst.begin(), 
                  lst.end(), checkLastName(lname)); 

if(it!=lst.end())
    std::cout<<" Found ";

With C++11, you can use lambda function as:

std::list<CPerson>::iterator it = 
          std::find_if(lst.begin(), 
                       lst.end(), 
                  [lname](CPerson const& ob){
                  return ob.getLastName().substr(0, lname.size()).compare(lname);
                                 }));

Answer 3

Simple use of find_if is shown in http://www.cplusplus.com/reference/algorithm/find_if/ with a simple predicate function (IsOdd). To add an argument you are probably better off using a function object (functor) or bind1st on a binary function http://www.cplusplus.com/reference/functional/bind1st/ .

If you are using C++11 you can use a lambda/anonymous function.