Assignment in C++ occurs despite exception on the right side

Question

I have some (C++14) code that looks like this:

map> junk;
for (int id : GenerateIds()) {
    try {
        set stuff =         


        

Answer 1

You're misunderstanding how operator[] works on std::map.

It returns a reference to the mapped item. Therefore, your code is first inserting a default item in that position and then invoking operator= to set a new value.

To make this work the way you expect, you'll need to use std::map::insert (*):

junk.insert(std::make_pair(id, GetStuff()));

Caveat: insert will only add the value if id is not already mapped.