How Can Two Variables at the Same Memory Address Hold Different Values Due to `const` and Compiler Optimizations?

Distinct Data at Shared Address: A Puzzle

In the provided code snippet, two variables seemingly occupy the same memory address but hold different values. To unravel this paradox, it's crucial to understand the semantics of const and the potential compiler optimizations that can redefine its behavior.

Const and Compiler Optimizations

The code initializes a const int variable N with a value of 22. Then, it obtains a pointer pN to the address of N by creatively casting a pointer to a const to a pointer to non-const. Subsequently, the value pointed to by pN is modified to 33, resulting in the siguientes output:

N: 22      Address: 0x22ff74
*pN: 33     Address: 0x22ff74

Apparently, both N and *pN have different values despite referencing the same memory location. This seeming contradiction stems from compiler optimizations that interpret const values as compile-time constants.

In this scenario, the compiler realizes that the value of N will never change. It optimizes the code to replace all references to N by its actual value, effectively bypassing the const designation. This optimization essentially converts:

*pN = 33;

into:

22 = 33;

Since this assignment is clearly invalid, the compiler reports an error. However, the code in question assigns the modified value to the location originally pointed to by pN. This behavior occurs because the compiler allows you to modify the memory pointed to by a const pointer, even though the pointed-to address is a const.

Thus, while N retains its original value of 22 due to its const designation, pN points to a location that has been modified to contain 33. Ultimately, despite occupying the same memory address, N and *pN hold distinct values, demonstrating the powerful role of compiler optimizations in shaping the execution of code.

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