difference between two ways to insert into map

Question

I was asked the two ways to insert a record to a map,

mymap["foo"] = 123;

mymap.insert("foo", 123);

so is there any difference between these two except the syntax?

Answer 1

In addition to Timo's excellent answer--

If no element at "foo" exists, the first will first default construct a value at the "foo" location, THEN using a reference to the default constructed "foo" value, assign 123 to that location.

Just doing

mymap["foo"]

will cause a value to be default constructed and placed at the "foo" location. So be careful when doing

int value = mymap["foo"]

because it will work, even if you never explicitly assigned or inserted at foo

Answer 2

There is, the first option via [] will overwrite the value stored with the key "foo" if a key "foo" exists, whereas insert will fail to insert data if the key already exists and will indicate success or failure in its return value.