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

std::map::operator[]

Returns a reference to the value that is mapped to a key equivalent to key, performing an insertion if such key does not already exist.

junk[id] causes the above mentioned insertion and after that has already happened GetStuff() throws. Note that in C++14 the order in which these things happen is implementation defined so with a different compiler your junk[id] = GetStuff(); may not do the insertion if GetStuff() throws.