STL map使用自定义对象做key

#include <map>using namespace std;struct grid{unsigned short x;unsigned short y;bool operator<(const grid& g)const{if ( y < g.y){return true;}                else if(y==g.y && x < g.x){return true;}return false;}};int _tmain(int argc, _TCHAR* argv[]){map<grid, int> lev;grid g;g.x = 0;g.y = 0;lev[g] = 1;g.x = 0;g.y = 1;lev[g] = 2;g.x = 1;g.y = 0;lev[g] = 3;g.x = 1;g.y = 1;lev[g] = 4;grid gg;gg.x = 1;gg.y = 0;int nn = lev[gg];return 0;}

STL中map，当使用自定义对象做key时，需要重载<操作符，示例