The C/C++ ternary operator is great:

int x = (someFlag) ? -1 : 1;

Delphi has a nice feature where preprocessor directives can be written on one line. Two examples:

x := {$IFDEF DBG_MY_SYMBOL} -1 {$ELSE} 1 {$ENDIF};
x := {$IF Defined(DBG_MY_SYMBOL)} -1 {$ELSEIF Defined(ANOTHER_SYMBOL)} 1 {$IFEND};

Beautiful!

Does C/C++ have a one-line equivalent like Delphi?

The C/C++ ternary operator is great:

int x = (someFlag) ? -1 : 1;

Delphi has a nice feature where preprocessor directives can be written on one line. Two examples:

x := {$IFDEF DBG_MY_SYMBOL} -1 {$ELSE} 1 {$ENDIF};
x := {$IF Defined(DBG_MY_SYMBOL)} -1 {$ELSEIF Defined(ANOTHER_SYMBOL)} 1 {$IFEND};

Beautiful!

Does C/C++ have a one-line equivalent like Delphi?

• c++
• delphi
• c-preprocessor
• preprocessor-directive

5 Answers 5

Does C/C++ have a one-line equivalent like Delphi?

Unfortunately, no. A C/C++ preprocessor directive takes up a whole line by itself, so there is no direct equivalent in C/C++ to your Delphi example.

However, in C/C++, expressions can span multiple lines, so you can do something like this instead:

x =
  #ifdef DBG_MY_SYMBOL
  -1
  #else
  1
  #endif
;

Or:

x = 
  #if defined(DBG_MY_SYMBOL)
  -1
  #elif defined(ANOTHER_SYMBOL)
  1
  #endif
;

That being said, you should consider using a separate constant for better readability, eg:

#ifdef DBG_MY_SYMBOL
const int MyConstant = -1;
#else
const int MyConstant = 1;
#endif

x = MyConstant;

Or:

#if defined(DBG_MY_SYMBOL)
const int MyConstant = -1;
#elif defined(ANOTHER_SYMBOL)
const int MyConstant = 1;
#endif

x = MyConstant;

Using always-defined macros

You can rely on dead code elimination in this case. Any modern compiler will optimize-out unused part of a branch, which as a constant expression as its condition. If you define the macros to have always a (numeric) value, instead of checking for their definedness, you can use the macro name in the C or C++ expression:

#define CONFIG_FOO 1
/* ⋮ or ⋮ */
#define CONFIG_FOO 0

int calculate_that(void)
{
    int the_foo     = 42;
    int the_not_foo = 24;
    return CONFIG_FOO ? the_foo : the_not_foo;
}

The hacky way

If you depend on use of #ifdef for checking values of your macros, consider using non-macro constants of value zero as the placeholder for disabled options. If you are generating your configuration header, this can be a particularly neat solution. When setting the #defines by hand, it will be cumbersome.

When both variable and the macro are defined, the macro will be used instead of the variable. Therefore, when you disable the option, it will fall back to zero.

Order of these two definitions could seem to be arbitrary, unless you define your macro after the first usage. But you must define the macro after defining the fallback value to not expand the macro name when setting the zero.

bindiff's personal note: Don't do that, pwease!