c++ what is "instantiated from here" error?

转载自Stack Overflow。

struct Data{
    Data(int a,int b){
        x = a;
        y = b;
    }
    int x;
    int y;
}
std::map m;
m[1] = Data(1,2);

compile error:
1: no matching function for call to "Data::Data()"
2: "instantiated from here" error;
Answers:There is no default constructor for struct Data. 
The map::operator[] returns a default constructed instance of its value type, in this case struct Data.

Either supply a default constructor:
Data() : x(0), y(0) {}
or use std::map::insert():
m.insert(std::pair(1, Data(1, 2)));

个人感想：当时也是同样的编译错误，编译器已经很明显了，提示构造函数形式不对，当时应该仔细分析一下
也应该可以想到的。以后得多多分析问题。