STL for_each,find_if用法

C/C++ code

    
    
    
    

     
     
     
     template
     
     
     
     <
     
     
     
     class
     
     
     
      InputIterator, 
     
     
     
     class
     
     
     
      Function
     
     
     
     >
     
     
     
      Function for_each(InputIterator first, InputIterator last, Function f) { 
     
     
     
     for
     
     
     
      ( ; first
     
     
     
     !=
     
     
     
     last; 
     
     
     
     ++
     
     
     
     first ) f(
     
     
     
     *
     
     
     
     first); 
     
     
     
     return
     
     
     
      f; }
    
    
    
    

上面是for_each的源码。
当
for_each(l.begin(),l.end(),print());的时候，print()是一个对象，没有名称的对象，
然后传递到f(*first)的时候，实际上就是print()(*first);
print()既然为一个对像，假定为a,也就是a(*first);而这就将调用operator().

 

/---------------------------------------for_each----------------------------------- #include <iostream> #include <list> #include <algorithm> using namespace std; struct print { int count; print(){count = 0;} void operator()(int x) {    cout << 3 * x << endl;    count++; } }; int main(void) { list<int> l; l.push_back(29); l.push_back(32); l.push_back(16); l.push_back(22); l.push_back(27); print p = for_each(l.begin(), l.end(), print()); cout << p.count << endl; return 0; } //--------------------------------find_if-------------------------------------------------------- #include <iostream> #include <list> #include <algorithm> using namespace std; bool divby5(int x) { return x % 5 ? 0 : 1; }; int main(void) { list<int> l; l.push_back(29); l.push_back(32); l.push_back(16); l.push_back(22); l.push_back(25); l.push_back(27); list<int>::iterator iLocation; iLocation = find_if(l.begin(), l.end(), divby5); if (iLocation != l.end()) {    cout << *iLocation << endl; } return 0; }