STL map使用自定义对象做key

[cpp]
#include

#include

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 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