Question

当地图在向量中时，有谁知道如何访问地图键/值？

struct ControlPointSet
{
  std::map<uint32_t,uint32_t> control_points;
}

当矢量看起来像这样：

void someMethod(const std::vector<ControlPointSet>& controlpoint_sets)
{
  //run through the map vector
  for(auto it = controlpoint_sets.begin(); it != controlpoint_sets.end(); it++)
     {
         for(int i = 0; i < it->control_points.size(); i ++)
         {
             std::cout << it->control_points.at(i) << std::endl;
         }
}

不知怎的，这不起作用

Answer 1

您无法按索引访问std::map个元素。它的at()方法取而代之的是输入密钥。

您可以使用iterator：

void someMethod(const std::vector<ControlPointSet>& controlpoint_sets)
{
    //run through the elements of the vector
    for(auto it = controlpoint_sets.begin(); it != controlpoint_sets.end(); ++it)
    {
        //run through the elements of a map
        for(auto cp = it->control_points.begin(); cp != it->control_points.end(); ++cp)
        {
            std::cout << cp->first << " " << cp->second << std::endl;
        }
    }
}

或range-based for loop：

void someMethod(const std::vector<ControlPointSet>& controlpoint_sets)
{
    //run through the elements of the vector
    for(const auto &cps : controlpoint_sets)
    {
        //run through the elements of a map
        for(const auto &cp : cps.control_points)
        {
            std::cout << cp.first << " " << cp.second << std::endl;
        }
    }
}

访问地图向量c ++

1 个答案: