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Condemned from their own mouths:
5.7 Conditionals with Omitted Operands
The middle operand in a conditional expression may be omitted.
Then if the first operand is nonzero, its value is the value of
the conditional expression.
Therefore, the expression
x ? : y
has the value of x if that is nonzero; otherwise, the value of y.
This example is perfectly equivalent to
x ? x : y
In this simple case, the ability to omit the middle operand is not
especially useful. When it becomes useful is when the first operand
does, or may (if it is a macro argument), contain a side effect.
Then repeating the operand in the middle would perform the side
effect twice. Omitting the middle operand uses the value already
computed without the undesirable effects of recomputing it.
Yes, it's useful. It is NOT, however, C. This kind of thing should require
compilation with "--butthead-extensions" and several embarassing "#pragma"
lines to make sure that it's NEVER used by anyone who isn't completely
aware they're being a wanker.
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