STL source code analysis stl_numeric.h

This article is senlie original, reproduced Please retain this address: http://blog.csdn.net/zhengsenlie

Description, source code, and example
Version 1: normal operation version
Version 2: General Operation version


1. accumulate
Description: calculates the sum of all elements in init and [first, last ).
Source code:

//version 1template <class InputIterator, class T>T accumulate(InputIterator first, InputIterator last, T init) {  for ( ; first != last; ++first)    init = init + *first;  return init;}//version 2template <class InputIterator, class T, class BinaryOperation>T accumulate(InputIterator first, InputIterator last, T init,             BinaryOperation binary_op) {  for ( ; first != last; ++first)    init = binary_op(init, *first);  return init;}

Example:

int main(){  int A[] = {1, 2, 3, 4, 5};  const int N = sizeof(A) / sizeof(int);  cout << "The sum of all elements in A is "        << accumulate(A, A + N, 0) // 15       << endl;  cout << "The product of all elements in A is "       << accumulate(A, A + N, 1, multiplies<int>()) //120       << endl;}

2. inner_product
Description: calculates the Inner Product of [first1, last1) and [first2, first2 + (last1-first1 ).
Source code:

//version 1template <class InputIterator1, class InputIterator2, class T>T inner_product(InputIterator1 first1, InputIterator1 last1,                InputIterator2 first2, T init) {  for ( ; first1 != last1; ++first1, ++first2)    init = init + (*first1 * *first2);  return init;}//version 2template <class InputIterator1, class InputIterator2, class T,          class BinaryOperation1, class BinaryOperation2>T inner_product(InputIterator1 first1, InputIterator1 last1,                InputIterator2 first2, T init, BinaryOperation1 binary_op1,                BinaryOperation2 binary_op2) {  for ( ; first1 != last1; ++first1, ++first2)    init = binary_op1(init, binary_op2(*first1, *first2));  return init;}

Example:

int main(){  int A1[] = {1, 2, 3};  int A2[] = {4, 1, -2};  const int N1 = sizeof(A1) / sizeof(int);  cout << "The inner product of A1 and A2 is "        << inner_product(A1, A1 + N1, A2, 0) //0       << endl;}

3. partial_sum
Description: calculates the local sum.
Source code:

//version 1template <class InputIterator, class OutputIterator, class T>OutputIterator __partial_sum(InputIterator first, InputIterator last,                             OutputIterator result, T*) {  T value = *first;  while (++first != last) {    value = value + *first;    *++result = value;  }  return ++result;}template <class InputIterator, class OutputIterator>OutputIterator partial_sum(InputIterator first, InputIterator last,                           OutputIterator result) {  if (first == last) return result;  *result = *first;  return __partial_sum(first, last, result, value_type(first));}//version 2template <class InputIterator, class OutputIterator, class T,          class BinaryOperation>OutputIterator __partial_sum(InputIterator first, InputIterator last,                             OutputIterator result, T*,                             BinaryOperation binary_op) {  T value = *first;  while (++first != last) {    value = binary_op(value, *first);    *++result = value;  }  return ++result;}template <class InputIterator, class OutputIterator, class BinaryOperation>OutputIterator partial_sum(InputIterator first, InputIterator last,                           OutputIterator result, BinaryOperation binary_op) {  if (first == last) return result;  *result = *first;  return __partial_sum(first, last, result, value_type(first), binary_op);}

Example:

int main(){  const int N = 10;  int A[N];  fill(A, A+N, 1);  cout << "A:                 ";  copy(A, A+N, ostream_iterator<int>(cout, " ")); // 1 2 3 4 5 6 7 8 9 10  cout << endl;   cout << "Partial sums of A: ";  partial_sum(A, A+N, ostream_iterator<int>(cout, " ")); // 1 3 6 10 15 21 28 36 45 55  cout << endl;}  

4. adjacent_difference
Description: calculates the difference between the adjacent elements of [first, last ).
Source code:

//version 1template <class InputIterator, class OutputIterator, class T>OutputIterator __adjacent_difference(InputIterator first, InputIterator last,                                      OutputIterator result, T*) {  T value = *first;  while (++first != last) {    T tmp = *first;    *++result = tmp - value;    value = tmp;  }  return ++result;}template <class InputIterator, class OutputIterator>OutputIterator adjacent_difference(InputIterator first, InputIterator last,                                    OutputIterator result) {  if (first == last) return result;  *result = *first;  return __adjacent_difference(first, last, result, value_type(first));}//version 2template <class InputIterator, class OutputIterator, class T,           class BinaryOperation>OutputIterator __adjacent_difference(InputIterator first, InputIterator last,                                      OutputIterator result, T*,                                     BinaryOperation binary_op) {  T value = *first;  while (++first != last) {    T tmp = *first;    *++result = binary_op(tmp, value);    value = tmp;  }  return ++result;}template <class InputIterator, class OutputIterator, class BinaryOperation>OutputIterator adjacent_difference(InputIterator first, InputIterator last,                                   OutputIterator result,                                   BinaryOperation binary_op) {  if (first == last) return result;  *result = *first;  return __adjacent_difference(first, last, result, value_type(first),                               binary_op);}

Example:

int main(){  int A[] = {1, 4, 9, 16, 25, 36, 49, 64, 81, 100};  const int N = sizeof(A) / sizeof(int);  int B[N];  cout << "A[]:         ";  copy(A, A + N, ostream_iterator<int>(cout, " ")); //1 4 9 16 25 36 49 64 81 100  cout << endl;    adjacent_difference(A, A + N, B);  cout << "Differences: ";  copy(B, B + N, ostream_iterator<int>(cout, " ")); // 3 5 7 9 11 13 15 17 19  cout << endl;  cout << "Reconstruct: ";  partial_sum(B, B + N, ostream_iterator<int>(cout, " ")); //1 4 9 16 25 36 49 64 81 100  cout << endl;}

5. Power
Description: calculates the N power of a certain number. SGI exclusive, not in STL Standard
Source code:

// Returns x ** n, where n> = 0. note that "multiplication" // is required to be associative, but not necessarily commutative. template <class T, class integer, class monoidoperation> T power (t x, integer N, monoidoperation OP) {// here Russian peasant algorithm if (n = 0) return identity_element (OP); else {While (N & 1) = 0) {n >>= 1; X = OP (x, x );} t result = x; n >>= 1; while (n! = 0) {x = OP (x, x); If (N & 1 )! = 0) Result = OP (result, x); N >>= 1 ;}return result ;}template <class T, class integer> inline t power (t x, integer N) {return power (x, N, multiplies <t> ());}

Example:

Int main () {cout <"2 ** 30 =" <power (2, 30) <Endl; // --> I cannot compile. The identifier power cannot be found. I have included <numeric>}

6. iota
Description: sets the content of a certain interval so that each element in the interval starts from the specified value and is displayed in ascending state.
Source code:

template <class ForwardIterator, class T>void iota(ForwardIterator first, ForwardIterator last, T value) {  while (first != last) *first++ = value++;}

Example:

int main(){  vector<int> V(10);  iota(V.begin(), V.end(), 7);  copy(V.begin(), V.end(), ostream_iterator<int>(cout, " ")); // 7 8 9 10 11 12 13 14 15 16  cout << endl; }