How is “const” implemented?

Question

How does a compiler, C or C++, (for example, gcc) honors the const declaration?

For example, in the following code, how does the compiler keeps trac

Answer 1

The compiler knows that ci is const because you told it so with the line

const int ci = get_foo();

As you pass ci around to other functions or assign it to other variables, the compiler preserves that const-ness by preventing you from doing anything that could potentially change its value.

For example, the following produces a compiler error.

int *ci2 = &ci;
(*ci2)++;

Because the compiler won't let you modify the value of ci.