std::transform || inner_product || accumulate

该问题归结为std::transform函数的使用

函数原型

template < class InputIterator, class OutputIterator, class UnaryOperator > OutputIterator transform ( InputIterator first1, InputIterator last1, OutputIterator result, UnaryOperator op ); template < class InputIterator1, class InputIterator2, class OutputIterator, class BinaryOperator > OutputIterator transform ( InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, OutputIterator result, BinaryOperator binary_op );

说明：

对于第一个原型：函数将对从输入参数的first1-last1的全部变量做op函数操作。结果保存到result中，或是通过返回值返回。

对于原形二：这个是对一的一个扩展，对于1这个只能对单个元素队列进行op操作，而第二个原形则是对对first1-last1上的元素和first2开始序列的元素逐个binary_op计算再保存到结果

示例

int op_inc(int num) { return ++i; }

int op_sum(int numa,int numb) { return a+b; }

int main()

{

vector<int >first;

vector<int >second;

vector<int >result;

.........//初始化过程省略,不过要注意当调用第二个原型的时候，保持队列二的长度要大于等于1

transform(first.begin(), first.end(), result.begin(), op_inc);

transform(first.begin(), first.end(), second.begin(), result.begin(), op_sum);

........//输出结果

return 0;

}

以上是transform的基本使用，接下来说明如何用它来处理字符串的大小写转换

事实上很简单，主要用到了，单个字符的大小写转换函数：tolower(),toupper()

不过对于大写转小写，同时小写转大写的要自己单独处理，函数如下

char exchange(char c)

{

if(c <= 'Z' && c >= 'A')

c = tolower(c);

else if(c >= 'a' && c <= 'z')

c = toupper(c);

return c;

}

示例

std::string str = "Http";

transform(str.begin(), str.end(), str.begin(), ::tolower); //将大写的都转换成小写
transform(str.begin(), str.end(), str.begin(), ::toupper); //将小写的都转换成大写
transform(str.begin(), str.end(), str.begin(), exchange);  //大小写切换

注以上结果都保存在str中。

+++

Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->#include <vector>#include <deque>#include <list>#include <iterator>#include <algorithm>using std::vector;using std::deque;using std::list;// Calculate the square of value.inline unsigned CalculateSquare(unsigned p_uiNumber){    return p_uiNumber*p_uiNumber;}// Entranceint main(){    vector<unsigned> vecUint;    const unsigned uiElementNumber = 6U;    for (unsigned i = 0U; i < uiElementNumber; ++i)    {        vecUint.push_back(i);    }    deque<unsigned> deqUint;    transform(vecUint.begin(), vecUint.end(), back_inserter(deqUint), CalculateSquare);    list<unsigned> lstUint;    transform(vecUint.begin(), vecUint.end(), deqUint.begin(), back_inserter(lstUint), std::multiplies<unsigned>());    return EXIT_SUCCESS;}

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inner_product

Visual Studio 2008

其他版本

Computes the sum of the element-wise product of two ranges and adds it to a specified initial value or computes the result of a generalized procedure where the sum and product binary operations are replaced by other specified binary operations.

template<class InputIterator1, class InputIterator2, class Type>   Type inner_product(      InputIterator1 _First1,       InputIterator1 _Last1,      InputIterator2 _First2,       Type _Val   );template<class InputIterator1, class InputIterator2, class Type,   class BinaryOperation1, class BinaryOperation2>   Type inner_product(      InputIterator1 _First1,       InputIterator1 _Last1,      InputIterator2 _First2,       Type _Val,       BinaryOperation1 _Binary_op1,       BinaryOperation2 _Binary_op2   );

 Parameters

---

_First1

An input iterator addressing the first element in the first range whose inner product or generalized inner product with the second range is to be computed.

_Last1

An input iterator addressing the last element in the first range whose inner product or generalized inner product with the second range is to be computed.

_First2

An input iterator addressing the first element in the second range whose inner product or generalized inner product with the first range is to be computed.

_Val

An initial value to which the inner product or generalized inner product between the ranges is to be added.

_Binary_op1

The binary operation that replaces the inner product operation of sum applied to the element-wise products in the generalization of the inner product.

_Binary_op2

The binary operation that replaces the inner product element-wise operation of multiply in the generalization of the inner product.

 Return Value

---

The first member function returns the sum of the element-wise products and adds to it the specified initial value. So for ranges of values ai and bi, it returns:

_Val + ( a₁ * b₁ ) + ( a₂ * b₂ ) +

by iteratively replacing _Val with _Val + (*a_i * *b_i ).

The second member function returns:

     _Val _Binary_op1 ( a₁ _Binary_op2 b₁ ) _Binary_op1 ( a₂ _Binary_op2 b₂ ) _Binary_op1

by iteratively replacing _Val with _Val _Binary_op1 (*a_i _Binary_op2 *b_i ).

难道刚好重载了上面这个？？？ _Val _Binary_op1 ( a₁ _Binary_op2 b₁ ) _Binary_op1

关于重载():

在这个例子中，二元函数对象divides()用第二个序列的元素除第一个序列中相对应的元素。因此，divides()接受的参考顺序为：

divides(first, second)

这种可以进行推广：当使用二元函数对象时，它的参数顺序是first，second。

 

创建函数对象Creating a Function Object

除了使用内置对象之外，你也可以创建自己的函数对象。要这样做，你仅需重载一个类的operator()函数。然而，出于最大灵活性考虑，你要使用下面由STL定义的一个类作为你的函数对象的基类。

template <class Argument, class Result> struct unary_function {

typedef Argument argument_type;

typedef Result result_type;

};

template <class Argument1, class Argument2, class Result>

struct binary_function {

typedef Argument1 first_argument_type;

typedef Argument2 second_argument_type;

typedef Result result_type;

};

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accumulate

Visual Studio 2008

其他版本

Computes the sum of all the elements in a specified range including some initial value by computing successive partial sums or computes the result of successive partial results similarly obtained from using a specified binary operation other than the sum.

template<class InputIterator, class Type>   Type accumulate(      InputIterator _First,       InputIterator _Last,       Type _Val   );template<class InputIterator, class Type, class BinaryOperation>   Type accumulate(      InputIterator _First,       InputIterator _Last,       Type _Val,       BinaryOperation _Binary_op   );

 Parameters

---

_First

An input iterator addressing the first element in the range to be summed or combined according to a specified binary operation.

_Last

An input iterator addressing the last element in the range to be summed or combined according to a specified binary operation that is one position beyond the final element actually included in the iterated accumulation.

_Val

An initial value to which each element is in turn added or combined with according to a specified binary operation.

_Binary_op

The binary operation that is to be applied to the each element in the specified range and the result of its previous applications.