C++ FAQ / Section 29 / FAQ 29.6

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Revised Jul 4, 2012

[29.6] What the heck is a const variable? Isn't that a contradiction in terms?

If it bothers you, call it a "const identifier" instead.

The main issue is to figure out what it is; we can figure out what to call it later. For example, consider the symbol max in the following function:

void f()
{
  const int max = 107;
  ...
  float array[max];
  ...
}

It doesn't matter whether you call max a const variable or a const identifier. What matters is that you realize it is like a normal variable in some ways (e.g., you can take its address or pass it by const-reference), but it is unlike a normal variable in that you can't change its value.

Here is another even more common example:

class Fred {
public:
  ...
private:
  static const int max_ = 107;
  ...
};

In this example, you would need to add the line int Fred::max_; in exactly one .cpp file, typically in Fred.cpp.

It is generally considered good programming practice to give each "magic number" (like 107) a symbolic name and use that name rather than the raw magic number.