Overloading the Comma Operator: When and How

Overloading the comma operator in C allows developers to customize its behavior, enabling non-standard operations. While it's primarily used for sequence point manipulations, it also presents practical applications.

One notable use case is indexing maps using multiple indices. For instance, the following code snippet demonstrates how a custom comma operator overload can simplify indexing a map with pairs of enum values:

enum Place {new_york, washington, ...};

pair operator , (Place p1, Place p2)
{
    return make_pair(p1, p2);
}

map, double> distance;

distance[new_york, washington] = 100;

By overloading the comma operator, developers can create meaningful and intuitive indexes, enhancing code readability and maintainability.

However, it's important to note that overloading the comma operator has limitations. In C 23, the use of the comma operator without enclosing parentheses in an array subscript has been deprecated and removed. This change aims to ensure consistent behavior and prevent potential ambiguities.