Why is #define bad and what is the proper substitute?

Question

#define dItemName        L\"CellPhone\"

Answer 1

Amusingly I could not find a single question pointing all the disadvantages, even the subject has certainly been discussed before.

First of all, not that in C (not C++) this is the way to declare a constant. This also explains why so many C++ developers still use it: when they come from C background or have been taught by / learned from people with C background, they tend to reproduce this C-ish behavior.

In C++, however, we have superior facilities.

#define does not define a constant, it defines a macro

1. A macro knows no scope
2. A macro is not type safe

A macro knows no scope:

They are preprocessing facilities: the preprocessor is not aware of the rules of the underlying language (whether asm, C or C++) and will always expand the symbols it has in stock with no regard for scope.

For this reason, it is usually recommended to use a specific set of symbols to set macros apart. People generally use ALL_CAPS symbols, though you need to remember that:

• they should not contain two consecutive underscores
• they should not begin by an underscore

in order to be compliant with the C++ standard.

A macro is not type safe.

As I said, the preprocessor ignores the underlying language rules, therefore the following does not strike it as strange:

#define FOO "foo"

int main(int argc, char* argv[])
{
  if (FOO) { ... }

  return 0;
}

On the other hand, using a proper type would prevent this unintentional mistake:

std::string const Foo = "foo";

Conclusion ?

You can use a #define if you wish, it's just you doing the extra work instead of the compiler, but that's your call. Personally: I am lazy :)