# V766. An item with the same key has already been added.

The analyzer detected the following strange situation: items are being added to a dictionary (containers of type 'map', etc.) or set (containers of type 'set', etc.) while having the same keys that are already present in these containers, which will result in ignoring the newly added items. This issue may be a sign of a typo and result in incorrect filling of the container.

Consider the following example with incorrect dictionary initialization:

    map<char, int> dict = map<char, int>{
      make_pair('a', 10),
      make_pair('b', 20),
      make_pair('a', 30)  // <=
    };

The programmer made a typo in the last line of the code performing dictionary initialization, as the 'a' key is already in the dictionary. As a result, this dictionary will contain 2 values, and the 'a' key will have the value 10.

To fix the error, we need to use a correct key value:

    map<char, int> dict = map<char, int>{
      make_pair('a', 10),
      make_pair('b', 20),
      make_pair('c', 30)
    };

A similar error may occur when initializing a set:

    set<string> someSet = set<string>{
      "First",
      "Second",
      "Third",
      "First", // <=
      "Fifth"
    };

A typo results in an attempt to write string 'First' instead of the 'Fourth' key to the 'someSet' set, but since this key is already in the set, it will be ignored.

To fix this error, we need to fix the initialization list:

    set<string> someSet = set<string>{
      "First",
      "Second",
      "Third",
      "Fourth",
      "Fifth"
    };

This diagnostic is classified as:

CWE-462

You can look at examples of errors detected by the V766 diagnostic.