如何判断输出迭代器是否被修改

发布于 2024-08-03 00:26:21 字数 875 浏览 2 评论 0原文

我有一个采用以下形式的模板函数：

template < class ITER1, class ITER2 >
bool example(ITER1 Input1, ITER1 Input2, ITER2 Output)
{
    ITER2 OrigOutput(Output);

    // ...

    std::copy(Input1, Input2, Output);

    return (OrigOutput != Output);
}

我像这样调用 example() ：

std::vector < int > Input;
std::set < int > Output;

if (example(Input.begin(), Input.end(), inserter(Output, Output.begin())))
{
    ...
}

我希望 example() 返回 true< /code> 如果元素已插入到 Output 中，但是我收到编译错误 (msvc 2008)：

Error 1 error C2678: binary '!=' : no operator found which takes a left-hand 
operand of type 'std::insert_iterator<_Container>' (or there is no acceptable 
conversion)

有没有办法确定是否有任何元素已插入到输出迭代器中为了返回正确的布尔值？

原文

I have a template function that takes the following form:

template < class ITER1, class ITER2 >
bool example(ITER1 Input1, ITER1 Input2, ITER2 Output)
{
    ITER2 OrigOutput(Output);

    // ...

    std::copy(Input1, Input2, Output);

    return (OrigOutput != Output);
}

And I'm calling example() like this:

std::vector < int > Input;
std::set < int > Output;

if (example(Input.begin(), Input.end(), inserter(Output, Output.begin())))
{
    ...
}

I'd like example() to return true if elements have been inserted into Output, however I'm getting a compile error (msvc 2008):

Error 1 error C2678: binary '!=' : no operator found which takes a left-hand 
operand of type 'std::insert_iterator<_Container>' (or there is no acceptable 
conversion)

Is there a way I can determine whether any elements were inserted into the output iterator in order to return the correct bool value?

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青柠芒果 2024-08-10 00:26:21

编写一个包装迭代器，它委派给另一个迭代器，您可以从插入迭代器构造该迭代器。然后，您的委托可以在 operator= 方法中将 modified 成员设置为 true。

类似这样的事情：

template<typename ITER>
class ModifiedIterator : public std::iterator<std::output_iterator_tag, void, void, void, void>
{
protected:
    typedef ITER Iter;
    Iter iter;
    bool& isModified;

public:
    explicit ModifiedIterator (Iter i, bool& isMod)
    : iter(i), isModified (isMod)
    {}

    template<typename T>
    ModifiedIterator& operator= (const T& value)
    {
        iter = value;
        ++iter;
        isModified = true;
        return *this;
    }

    ModifiedIterator& operator* () { return *this; }
    ModifiedIterator& operator++ () { return *this; }
    ModifiedIterator operator++ (int) { return *this; }
};

Write a wrapper iterator which delgates to another iterator, which you would construct from your insert iterator. Your delegate then can set a modified member to be true in the operator= method.

Something along the lines of this:

template<typename ITER>
class ModifiedIterator : public std::iterator<std::output_iterator_tag, void, void, void, void>
{
protected:
    typedef ITER Iter;
    Iter iter;
    bool& isModified;

public:
    explicit ModifiedIterator (Iter i, bool& isMod)
    : iter(i), isModified (isMod)
    {}

    template<typename T>
    ModifiedIterator& operator= (const T& value)
    {
        iter = value;
        ++iter;
        isModified = true;
        return *this;
    }

    ModifiedIterator& operator* () { return *this; }
    ModifiedIterator& operator++ () { return *this; }
    ModifiedIterator operator++ (int) { return *this; }
};

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