我想在for_each的时候把满足equal函数的条件的变量加到list里：

Advertisement* equal(Listing &list, string keyword)(Advertisement* ad)
{
    if (ad->getTitle().find(keyword.c_str()) != -1)
        list.add(ad);
    return ad;
}

Listing Listing::filter(string keyword)
{
    if (keyword == "")
        return *this;

    Listing list;
    for_each(this->begin(), this->end(), equal(list,keyword));

谢谢你，我的问题已经解决了。我用了一个类
// A class that used for accept the function parameters
class Equal
{
private:
    string keyword;        // The value of keyword
    Listing &list;        // The list to add Advertisement*
public:
    // Constructor initializes the value of Listing list and string keyword
    Equal (Listing &init_list  ,const string init_keyword)
        : list(init_list) ,keyword ( init_keyword )
    {}

    // The function call for the element
    void operator ( ) ( Advertisement* elem ) const
    {
        if (elem->getTitle().find(keyword) != -1 ||
            elem->getBody().find(keyword) != -1)
        {
            list.add(elem);
        }
    }
};

// Return a Listing object that contains those advertisements
// whose name or description contains keyword
Listing Listing::filter(string keyword)
{
    if (keyword == "")
        return *this;

    Listing list;
    for_each(this->begin(), this->end(), Equal(list, keyword));

    return list;
}