More on const
const is tricky enough that it deserves some study.

Unlike C, in C++ constreally is constant. The following declarations work in C++ but not in C:

const int maxn = 1000; int a[maxn + 1];

//#define maxn 1000

const pointer vspointer to const vsconst pointer to const

When pointers and const are involved in the same declaration, what does it mean? Does it mean the pointer doesn't change (const pointer)? Does it mean the thing the pointer points at doesn't change (pointer to const)? Or does it mean neither the pointer nor the thing it points at can change? Not so clear, but luckily, it is possible to express all three concepts in C++:

int i = 1, j = 3;
int* const p = &i; const int* q = &i; const int* const r = &i;

// const pointer
// pointer to const // const pointer to const

*p = 5; p = &j; *q = 5; q = &j; *r = 5; r = &j;

// okay
// error, p is read-only pointer
// error, thing pointed to by q? // okay
// error, like *q = 5
// error,

const reference variables
You can have a reference to an object, yet tell the compiler you don't want use of this reference to change the variable.

22-Mar-98

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