How Do I Compare Pointers for Equality in C ?

Determining Object Equality Between Pointers

In C , the comparison of two pointers using the equality operator (==) depends on their respective objects.

Pointers to Objects

For pointers (a and b) pointing to objects of the same type, the equality operation (a == b) returns true in the following cases:

• Both pointers are null
• Both pointers point to the same object in memory
• Both pointers represent the same address

Pointers to Functions

If the pointers point to functions of the same type, the comparison also returns true if they point to the same function.

Pointers to Array Elements

When pointers point to elements within an array, the comparison returns true if they refer to the same element or are one past the last element of the same array.

Unspecified Comparisons

In certain scenarios, the behavior of the equality operator for pointers is unspecified. This includes:

• Comparison of pointers to object members of different access levels
• Comparison of pointers to non-static data members of union objects
• Comparison of pointers to non-local variables in different functions

Standard Library's Extension

The C Standard Library provides the std::less<> template, which offers a global ordering for any pointer type, regardless of the comparison behavior defined by the built-in operators. This allows for consistent comparisons of void pointers.

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