Question

typedef map<int, string> iMap;
typedef map<double, innerMap> OutMap;

OutMap mx;

map<double, iMap >::iterator it_out;
map<int, string>::iterator it_i;

for ( it_out=mx.begin() ; it_out != mx.end(); it_out++ ) {
   cout << "\n\nNew element\n" << (*it_out).first << endl;
   for( it_i=(*it_out).second.begin(); it_i != (*it_out).second.end(); it_out++)
     cout << (*it_i).first << " => " << (*it_i).second << endl;
}

I’m pretty sure the above code is fine…
Is there any performance issue…?

Answer 1

It cannot be improved further, except that

• You can use pre-increment instead of post-increment, i.e ++it_out instead of it_out++.
• You can use '\n' instead of endl in the cout. Using '\n' would improve the performance of output operation by reasonable margin, because endl first puts '\n' in the output buffer, and then flushes it to the destination (stdout in this case) which makes it slow operation.

Note that you should increment it_i (as opposed to it_out) in the inner for loop. I suppose that is a typo.