STL often uses traversal algorithms for_each and transform.

For_each () and transform () algorithms compare
1) STL Algorithm – Modified algorithm
For_each ()
Copy ()
Copy_backward ()
Transform ()
Merge ()
Swap_ranges ()
Fill ()
Fill_n ()
Generate ()
Generate_n ()
Replace
Replace_if ()
Replace_copy ()
Replace_copy_if ()
2)
For_each () speed is not flexible
Transform () Slow and flexible

Normal: The function object used by For_each, which is a reference, no return value
The function object used by the transform, which generally does not use references, but also return values

int showElem2 (int n) {cout << n << ""; return n;} void Main43_transform_pk_foreach () {vector<int> v1;v1.push_back (1); V1.push_back (3); V1.push_back (5); vector <int> v2 = V1;for_each (V1.begin (), V1.end (), Showelem),//transform Requirements for function objects/*c:\program Files\Microsoft Visual Studio 10.0\vc\include\algorithm (1119): See Instantiating a function template that is being compiled "_outit std::_transform1<int*,_outit,void (__cdecl *) (int &) > (_init,_init,_outit,_fn1,std::tr1::true_type) reference 1> with1> [1> _outit=st              D::_vector_iterator<std::_vector_val<int,std::allocator<int>>>,1> _InIt=int *,1> _fn1=void (__cdecl *) (int &) 1>]*//*template<class _init,class _outit,class _fn1> Inline_ou  Tit _transform (_init _first, _init _last,_outit _dest, _fn1 _func) {//Transform [_first, _last) with _funcfor (; _first! = _last;  ++_first, ++_dest) *_dest = _func (*_first); Explains why there is a return value of returns (_dest);} */transform (V2.begin (),V2.end (), V2.begin (), showElem2);} 

The demo demonstrates the use of for_each and transform algorithms in a complete way. And

#include <iostream> #include <cstdio> #include <vector> #include <list> #include <algorithm > #include <functional> #include <iterator>using namespace Std;class cmyshow{public:cmyshow () {num = 0;} void operator () (int &n) {num++;cout << n << "";} void Printnum () {cout << "num:" << num << Endl;} Protected:private:int num;};  void Printv (vector<int> &v) {for (Vector<int>::iterator it = V.begin (); It! = V.end (); it++) {cout << *it << "";} cout << Endl;} void Printlist (list<int> &v) {for (List<int>::iterator it = V.begin (); It! = V.end (); it++) {cout << * It << "";} cout << Endl;} void Showelem (int &n) {cout << n << "";} For_each function Use method void Play_for_each () {vector<int> v1;v1.push_back (1); V1.push_back (3); V1.push_back (5);p Rintv (v1); cout << endl;/*template<class _init,class _fn1> inline_fn1 for_each (_init _first, _init _Last, _Fn1 _Fun c) {//Perform function for each element_debug_range (_first, _last); _debug_pointer (_func); return (_for_each (_unchecked (_ First), _unchecked (_last), _func);} *///Function Object callback function entry address For_each (V1.begin (), V1.end (), Showelem), cout << Endl;for_each (V1.begin (), V1.end (), Cmyshow () ); cout << Endl; Cmyshow Mya; Cmyshow my1 = For_each (V1.begin (), V1.end (), MYA);  Initialize Mya.printnum () to my1;  MA1 and My1 are two different objects my1.printnum (); my1 = For_each (V1.begin (), V1.end (), MYA); Assign a value to My1 my1.printnum ();} int increase (int i) {return i + 100;} Transform function Use method void Play_transform () {vector<int> v1;v1.push_back (1); V1.push_back (3); V1.push_back (5); Printv (v1); cout << Endl;//transform Use callback Functions transform (V1.begin (), V1.end (), V1.begin (), increase);p Rintv (v1); cout << endl;//transform Use a predefined function object transform (V1.begin (), V1.end (), V1.begin (), negate<int> ());p Rintv (v1 ); cout << endl;//transform use function adapters and function Objects list<int> mylist;mylist.resize (V1.size ()), transform (V1.begin (), V1.end (), Mylist.begin (), bind2nd (Multiplies<int> ()));p rintlist (mylist), cout << Endl;//transform can also output the results of the operation directly to the screen transform ( V1.begin (), V1.end (), ostream_iterator<int> (cout, ""), negate<int> ()); cout << Endl;} Under normal circumstances: The function object used by the For_each, the reference is the parameter. There is no function object for the return value//transform, the reference is generally not used, but there is a return value of int showElem2 (int n) {cout << n << ""; return n;} void Play_transform_pk_foreach () {vector<int> v1;v1.push_back (1); V1.push_back (3); V1.push_back (5);vector< Int> v2 = V1;for_each (V1.begin (), V1.end (), Showelem),//transform Requirements for function objects/*c:\program Files\Microsoft Visual Studio 10.0\vc\include\algorithm (1119): See the instantiation of a function template being compiled "_outit std::_transform1<int*,_outit,void (__cdecl *) (int &) > (_init,_init,_outit,_fn1,std::tr1::true_type) "Reference 1> with1> [1> _outit=std::_ve              Ctor_iterator<std::_vector_val<int,std::allocator<int>>>,1> _InIt=int *,1> _fn1=void (__cdecl *) (int &) 1>]*//*template<class _InIt,class _OutIt,class _Fn1> inline_OutIt _Transform(_InIt _First, _InIt _Last,_OutIt _Dest, _Fn1 _Func  ) {//Transform [_first, _last) with _funcfor (; _first! = _last; ++_first, ++_dest) *_dest = _func (*_first); Explains why there is a return value of returns (_dest);} */transform (V2.begin (), V2.end (), V2.begin (), showElem2);} int main () {Play_for_each ();p lay_transform ();p Lay_transform_pk_foreach (); return 0;}

STL often uses traversal algorithms for_each and transform.