一、accumulate
作用：初始化init，对区间[first，last）的迭代器i执行init += *i或init = binaryop（init，*i）。
template <class _InputIterator, class _Tp>//版本1，用来计算init和[first，last)区间元素的总和 _Tp accumulate(_InputIterator __first, _InputIterator __last, _Tp __init) { for ( ; __first != __last; ++__first) __init = __init + *__first; return __init; } template <class _InputIterator, class _Tp, class _BinaryOperation>//版本2，对迭代器中每一个元素时执行二元操作 _Tp accumulate(_InputIterator __first, _InputIterator __last, _Tp __init, _BinaryOperation __binary_op) { for ( ; __first != __last; ++__first) __init = __binary_op(__init, *__first); return __init; } 二、inner_product作用：初始化init，对区间[first1，last1）和[first2，first2+（last1-first1））的两个迭代器i和j执行init += *i**j或init = binaryop1（init，binaryop1（*i，*j））。
template <class _InputIterator1, class _InputIterator2, class _Tp>//版本1，两个迭代器元素的内积 _Tp inner_product(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _Tp __init) { for ( ; __first1 != __last1; ++__first1, ++__first2) __init = __init + (*__first1 * *__first2); return __init; } template <class _InputIterator1, class _InputIterator2, class _Tp, class _BinaryOperation1, class _BinaryOperation2> //版本2，两个迭代器的二元操作，提供operator+和operator* _Tp inner_product(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _Tp __init, _BinaryOperation1 __binary_op1, _BinaryOperation2 __binary_op2) { for ( ; __first1 != __last1; ++__first1, ++__first2) __init = __binary_op1(__init, __binary_op2(*__first1, *__first2)); return __init; } 三、partial_num作用：局部计算总和，*first赋值给*result，*first+*（first+1）赋值给*（result+1），依次类推，直至first==last。原始序列为[1,2,3,4,5],执行后得到[1,3,6,10,15]。
template <class _InputIterator, class _OutputIterator, class _Tp> _OutputIterator __partial_sum(_InputIterator __first, _InputIterator __last, _OutputIterator __result, _Tp*) { _Tp __value = *__first; while (++__first != __last) { __value = __value + *__first; *++__result = __value;//记录每次两个元素相加的值 } return ++__result; } template <class _InputIterator, class _OutputIterator>//版本1 _OutputIterator partial_sum(_InputIterator __first, _InputIterator __last, _OutputIterator __result) { if (__first == __last) return __result;//没有元素返回空 *__result = *__first;//*first赋值给result第一个元素 return __partial_sum(__first, __last, __result, __VALUE_TYPE(__first));//result从第二个元素开始记录两两相加的结果 } template <class _InputIterator, class _OutputIterator, class _Tp, class _BinaryOperation> _OutputIterator __partial_sum(_InputIterator __first, _InputIterator __last, _OutputIterator __result, _Tp*, _BinaryOperation __binary_op) { _Tp __value = *__first; while (++__first != __last) { __value = __binary_op(__value, *__first);//两两元素执行二元操作 *++__result = __value; } return ++__result; } template <class _InputIterator, class _OutputIterator, class _BinaryOperation>//版本2 _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); } 四、adjacent_difference作用：计算相邻元素的差。原始序列为[1,2,3,4,5],执行partial_num后得到[1,3,6,10,15],再执行adjacent_difference后得到[1,2,3,4,5]。
template <class _InputIterator, class _OutputIterator, class _Tp> _OutputIterator __adjacent_difference(_InputIterator __first, _InputIterator __last, _OutputIterator __result, _Tp*) { _Tp __value = *__first; while (++__first != __last) { _Tp __tmp = *__first; *++__result = __tmp - __value;//计算相邻元素的差额 __value = __tmp; } return ++__result; } template <class _InputIterator, class _OutputIterator>//版本1 _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)); } template <class _InputIterator, class _OutputIterator, class _Tp, class _BinaryOperation> _OutputIterator __adjacent_difference(_InputIterator __first, _InputIterator __last, _OutputIterator __result, _Tp*, _BinaryOperation __binary_op) { _Tp __value = *__first; while (++__first != __last) { _Tp __tmp = *__first; *++__result = __binary_op(__tmp, __value);//相邻元素的二元操作 __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); } 五、power（SGI专属，不在STL之列）作用：指定元素的n次方
template <class _Tp, class _Integer> inline _Tp __power(_Tp __x, _Integer __n) { return __power(__x, __n, multiplies<_Tp>());//指定操作为乘法，则为乘幂 } template <class _Tp, class _Integer, class _MonoidOperation>//幂次方 inline _Tp power(_Tp __x, _Integer __n, _MonoidOperation __opr) { return __power(__x, __n, __opr); } template <class _Tp, class _Integer> inline _Tp power(_Tp __x, _Integer __n) { return __power(__x, __n); } 六、itoa（SGI专属，不在STL之列）作用：设定某个区间内容
template <class _ForwardIter, class _Tp> void iota(_ForwardIter __first, _ForwardIter __last, _Tp __value) { while (__first != __last) *__first++ = __value++; }