“:-!!” what is it in c code?

The actual line is <i>#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); }))</i><p>The guy asking the question just misread the code, the colon is part of the struct definition and the key part is -!! which coerces an integer to 0 if the value is zero, or -1 if the value is anything other than 0.

These machinations were always necessary to get compile-time asserts. Luckily C++11 and C11 are both providing static_assert so there will be <i>real</i> compiler support instead of having to trick it into dumping an error.<p>edit: Another common one is using __LINE__ or __COUNTER__ in an array symbol name and having the test value result in an array size of -1.

Reminds me of the 'goes to' operator:<p><pre><code> for (int i = 42; i --&#62; 0;) { foo(); }</code></pre>

This has been posted before during the past 2 months.