将字符串按照长短从小到大排序

bool isShorter(   const string &s1, const string &s2    )
{
    return s1.size( ) < s2.size( )  ;
}
int  main(   )
{
    vector<string>  sVec{ "the","quick","red","fox","jumps","over","the","slow","red","turtle" };
    sort(sVec.begin(), sVec.end(), isShorter );
    for (vector<string>::iterator i = sVec.begin(); i != sVec.end(); ++i) {
        cout << *i << "  ";
    }cout << endl;

    return 0;
}

C++标准库算法从小到大排序，sort( s.begin(),s.end(),isShorter )为什么没有向isShorter函数传递参数。