The analyzer detected a potential error of working with classes that contain operator[].
Classes with an overloaded operator[] are usually a kind of an array where the index of the item being called is operator[] argument. If operator[] has a 32-bit type formal argument but memsize-type is used as an actual argument, it might indicate an error. Let us consider an example leading to the warning V120:
class MyArray { int m_arr[10]; public: int &operator;[](unsigned i) { return m_arr[i]; } } Object; size_t k = 1; Object[k] = 44; //V120
This example does not contain an error but might indicate an architecture shortcoming. You should either work with MyArray using 32-bit indexes or modify operator[] so that it takes an argument of size_t type. The latter is preferable because memsize-types not only serve to make a program safer but sometimes allow the compiler to build a more efficient code.