Question

#include <initializer_list>
#include <iostream>
#include <vector>

//this api is anti intuition
void original(int const **data)
{
    for(size_t i = 0; i != 3; ++i){
        int const *ptr = *data;
        //std::cout<<*ptr++<<", "<<*ptr<<std::endl; //this line may cause undefined behavior
        std::cout<<ptr[0]<<", "<<ptr[1]<<std::endl;
        ++data;
    }
}

//my eyes prefer this api than original like api
void replace_original(std::initializer_list<std::initializer_list<int>> list)
{
    std::vector<int const*> results(list.size());        

    for(auto data : list){        
        results.push_back(std::begin(data)); //#1
    }

    original(&results[0]);
}

int main()
{         
    int first[] = {0, 1};
    int second[] = {2, 3};
    int third[] = {4, 5};

    int const *array[] = {first, second, third};
    original(array);
    replace_original({ {0, 1}, {2, 3}, {4, 5} });

    return 0;
}

结果

0, 1
2, 3
4, 5

预期结果

0, 1
2, 3
4, 5
0, 1
2, 3
4, 5

我想用api替换原始（旧的，c风格的api）的api，如replace_original 但无法弄清楚为什么＃1无法正常工作。

Answer 1

啊，愚蠢的错误，我应该把循环改为

    size_t const size = list.size();
    std::vector<int const*> results(size);
    for(size_t i = 0; i != size; ++i){
        results[i] = std::begin( *(std::begin(list) + i) );
    }

你有更好的解决方案来封装这种api吗？谷歌之后，我发现在c ++ 14中，initializer_list的size（）会成为constexpr所以我们应该能够使用std :: array来替换std :: vector

通过initializer_list将指针替换为指针

1 个答案: