A typecast to void? or what? and why?

Question

I was looking llvm clang's implementation of the C++ standard library...
In file mutex.cpp I found the following code:

void
mutex::unlock() _NOEXCEPT
{
    int ec = pthread_mutex_unlock(&__m_);
    (void)ec;                              // What??, Why??? O.o
    assert(ec == 0);
}

I don't understand what that expression is doing and why...
I need some explanation.

Probably to avoid compiler warning about unused variable. – Maroun Aug 14 '14 at 21:01 — Maroun, Aug 14 '14 at 21:01

Vlad from Moscow · Accepted Answer · 2014-08-14T21:07:40.747

4

I think that this expression is used that to avoid a compiler warning that the variable was declared but was not used.

As user2864740 pointed out the assert statement in this code can be a mcaro that in some conditions does not use the variable. That is it can be expanded to an empty statement.

edited Aug 14 '14 at 21:07

answered Aug 14 '14 at 21:00

Vlad from Moscow

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+1 I confirm it too, I use it all the time to silent the compiler. – 101010 Aug 14 '14 at 21:03

A typecast to void? or what? and why?

1 Answers1