Question

本书中的示例副本：

#include "stdafx.h"
#include<functional>
#include<iostream>
#include <vector>
#include <algorithm>
#include<iterator>

using namespace std;

template<typename input_iterator_tag, typename output_iterator_tag,
typename elem_type, typename comp>
output_iterator_tag
filter(input_iterator_tag first, output_iterator_tag last,
output_iterator_tag at, const elem_type &val, comp pred)
{
    while ((first = find_if(first, last, bind2nd(pred, val))) != last)
    {
        cout << "found value: " << *first << endl;
        *at++ = *first++;
    }
    return at;
 }

 int _tmain(int argc, _TCHAR* argv[])
{
const int elem_size = 8;
int ia[elem_size] = { 12, 8, 43, 0, 6, 21, 3, 7 };
vector<int>ivec(ia, ia + elem_size);

int ia2[elem_size];
vector<int>ivec2(elem_size);

cout << "filtering integer array for values less than 8\n";
filter(ia, ia + elem_size, ia2, elem_size, less<int>());
cout << "filtering integer vector for value greater than 8\n";
filter(ivec.begin(), ivec.end(), ivec2.begin(), elem_size, greater<int>  ());//it's work ok
filter(ivec.begin(), ivec.end(), back_inserter(ivec2), elem_size, greater<int>());//compile error,no instance of function template "filter" matches 

system("pause");
return 0;
}

为什么我使用“back_inserter（ivec2）”替换“ivec2.begin（）”如本书所说，但它无法在visual studio中编译;

   IntelliSense: no instance of function template "filter" matches the argument list argument types are: (std::_Vector_iterator<std::_Vector_val<std::_Simple_types<int>>>, std::_Vector_iterator<std::_Vector_val<std::_Simple_types<int>>>, std::back_insert_iterator<std::vector<int, std::allocator<int>>>, const int, std::greater<int>)

任何人都可以帮我纠正它，为什么？

Answer 1

看起来像是函数声明中的拼写错误。第二个参数（last）应该是input_iterator_tag而不是output_iterator_tag，因为它应与first迭代器匹配，因为它直接与first进行比较。< / p>

template<typename input_iterator_tag, typename output_iterator_tag,
typename elem_type, typename comp>
output_iterator_tag
filter(input_iterator_tag first, input_iterator_tag last,
output_iterator_tag at, const elem_type &val, comp pred)

注意：它适用于您的第一个案例的原因是输入和输出类型都相同。

“Essential C ++”ch3.9使用“back_inserter（ivec2）”替换“ivec2.begin（）”无法编译

1 个答案: