c++ - 给Qt中距离最小的点一个标志的语义错误

Question

我正在做一个 qt 项目。我正在计算用户点击鼠标输入的每个点与我声明的一些虚拟点之间的距离。该点将采用具有最小距离的虚拟点的标志。我的项目中存在语义错误。我试图追踪代码，但我不明白为什么会这样。问题是我总是得到标志 1。当我输入 2 点时，我得到标志 11。它总是 1。

当我调试 2 点时:

138 ,  134 
distance 1  0 
distance 2 7 
distance 3  14 
distance 4 5 
distance 5  8.60233 
distance 6  14.8661 
flag  " 1" 
183 ,  168 
distance 1  56.4004 
distance 2 52.4786 
distance 3  49.2443 
distance 4 52.4976 
distance 5  48.2597 
distance 6  44.7214 
flag  " 11" 

我觉得问题出在这里:

      if (min_distance== distance_pt_1 ){
      char_flag=char_flag.append("1");
      }
      else  if (min_distance== distance_pt_2 ){
  char_flag=char_flag.append("2");
 }
      else  if (min_distance== distance_pt_3 ){
  char_flag=char_flag.append("3");
 }
      else  if (min_distance== distance_pt_4 ){
  char_flag=char_flag.append("4");
 }
      else  if (min_distance== distance_pt_5 ){
  char_flag=char_flag.append("5");
 }
      else  if (min_distance== distance_pt_6 ){
  char_flag=char_flag.append("6");
 }

      qDebug()<<"flag " <<char_flag;

开头的代码:

 foreach( QGraphicsItem * item, list )
     {
             min_distance=scene->width();
             distance_pt_1=scene->width();
             distance_pt_2=scene->width();
             distance_pt_3=scene->width();
             distance_pt_4=scene->width();
             distance_pt_5=scene->width();
             distance_pt_6=scene->width();

              int xx=item->x();
              int yy=item->y();
              qDebug()<<xx<<", "<< yy;

        distance_pt_1=qSqrt(qPow(xx- pt_1.x(),2)+qPow(yy- pt_1.y(),2));
        distance_pt_2=qSqrt(qPow(xx- pt_2.x(),2)+qPow(yy- pt_2.y(),2));
        distance_pt_3=qSqrt(qPow(xx- pt_3.x(),2)+qPow(yy- pt_3.y(),2));
        distance_pt_4=qSqrt(qPow(xx- pt_4.x(),2)+qPow(yy- pt_4.y(),2));
        distance_pt_5=qSqrt(qPow(xx- pt_5.x(),2)+qPow(yy- pt_5.y(),2));
        distance_pt_6=qSqrt(qPow(xx- pt_6.x(),2)+qPow(yy- pt_6.y(),2));

              if (distance_pt_1 < min_distance)
         {
             min_distance= distance_pt_1;

         }
              else  if (distance_pt_2 < min_distance)
         {
             min_distance= distance_pt_2;

         }
              else  if (distance_pt_3 < min_distance)
         {
             min_distance= distance_pt_3;

         }
              else  if (distance_pt_4 < min_distance)
         {
             min_distance= distance_pt_4;

         }
              else  if (distance_pt_5 < min_distance)
         {
             min_distance= distance_pt_5;

         }
              else  if (distance_pt_6 < min_distance)
         {
             min_distance= distance_pt_6;

         }



      if (min_distance== distance_pt_1 ){
  char_flag=char_flag.append("1");
 }
      else  if (min_distance== distance_pt_2 ){
  char_flag=char_flag.append("2");
 }
      else  if (min_distance== distance_pt_3 ){
  char_flag=char_flag.append("3");
 }
      else  if (min_distance== distance_pt_4 ){
  char_flag=char_flag.append("4");
 }
      else  if (min_distance== distance_pt_5 ){
  char_flag=char_flag.append("5");
 }
      else  if (min_distance== distance_pt_6 ){
  char_flag=char_flag.append("6");
 }

      qDebug()<<"flag " <<char_flag;

  } // foreach loop

Answer 1

由于您使用的是 if - else if，因此并未检查您的所有条件。这意味着第一个条件始终为真(distance_pt_1 小于初始的 min_distance)，但永远不会评估下一个条件。只需删除 else 子句即可。

if (distance_pt_1 < min_distance) {
    min_distance = distance_pt_1;
}
if (distance_pt_2 < min_distance) {
    min_distance = distance_pt_2;
}
if (distance_pt_3 < min_distance) {
    min_distance = distance_pt_3;
}
if (distance_pt_4 < min_distance) {
    min_distance = distance_pt_4;
}
if (distance_pt_5 < min_distance) {
    min_distance = distance_pt_5;
}
if (distance_pt_6 < min_distance) {
    min_distance = distance_pt_6;
}