Question

我有一个在std :: string中形成的查询字符串，查询有4个点，每个点都有一个x，y，每个点都是double数据类型。

如何连接字符串以将4个点（8个变量）放在c ++中的查询中

'MULTIPOINT(16.17951 47.85549, 16.17951 47.85549, 16.17951 47.85549, 16.17951 47.85549)';

这是查询的形式：

string query = "SELECT * from areas WHERE st_contains(ST_ConvexHull(areas.GEOMETRY),st_mpointfromtext('MULTIPOINT(16.17951 47.85549, 16.17951 47.85549, 16.17951 47.85549, 16.17951 47.85549)',4326));";




double x1 = 6.17951, x2 = 6.17951, x3 = 6.17951, x4 = 6.17951;
double y1 = 7.85549, y2 = 7.85549, y3 = 7.85549, y4 = 7.85549;

    /* std::string query = "SELECT * from areas WHERE st_contains(ST_ConvexHull(areas.GEOMETRY),st_mpointfromtext('MULTIPOINT(" 
                    + to_string(x1) + " " + to_string(y1) + ", " 
                    + to_string(x2) + " " + to_string(y2) + ", " 
                    + to_string(x3) + " " + to_string(y3) + ", " 
                    + to_string(x4) + " " + to_string(y4) + "',4326));";
 */

    string query = "SELECT * from areas WHERE st_contains(ST_ConvexHull(areas.GEOMETRY),st_mpointfromtext('MULTIPOINT(6.17951 7.85549, 6.17951 7.85549, 6.17951 7.85549, 6.17951 7.85549)',4326));";

Answer 1

根据您的输入类型，有几个选项。

如果您有std::string mp = "'MULTIPOINT(16.17951 47.85549, 16.17951 47.85549, 16.17951 47.85549, 16.17951 47.85549)'"; std::string query = "SELECT * from areas WHERE st_contains(ST_ConvexHull(areas.GEOMETRY),st_mpointfromtext(" + mp + ",4326));";，请执行以下操作：

doubles

如果您的输入为C++11，并且您使用std::string query = "SELECT * from areas WHERE st_contains(ST_ConvexHull(areas.GEOMETRY),st_mpointfromtext('MULTIPOINT(" + std::to_string(x1) + " " + std::to_string(y1) + ", " + std::to_string(x2) + " " + std::to_string(y2) + ", " + std::to_string(x3) + " " + std::to_string(y3) + ", " + std::to_string(x4) + " " + std::to_string(y4) + ")',4326));";，那么您可以这样做：

export class XComponent{
     someProp: string;
     someList: string[];
     someFn(){
          this.someService.subscribe(
               data=>{
                    this.someProp = data.prop; 
                    this.someList = data.list;
               }
          );
     }
}

串联字符串最好的方法是什么？

1 个答案: