Do you use curly braces for additional scoping? [c

Question

I mean other than using it when required for functions, classes, if, while, switch, try-catch.

I didn't know that it could be done like this until I saw this SO question.

In the above link, Eli mentioned that "They use it to fold up their code in logical sections that don't fall into a function, class, loop, etc. that would usually be folded up."

What other uses are there besides those mentioned?

Is it a good idea to use curly braces to limit the scope of your variables and expand the scope only if required (working on a "need-to-access" basis)? Or is it actually silly?

How about using scopes just so that you can use the same variable names in different scopes but in the same bigger scope? Or is it a better practise to reuse the same variable (if you want to use the same variable name) and save on deallocating and allocating (I think some compilers can optimise on this?)? Or is it better to use different variable names altogether?

Answer 1

As others have said, this is fairly common in C++ due to the all-powerful RAII (resource acquisition is initialization) idiom/pattern.

For Java programmers (and maybe C#, I don't know) this will be a foreign concept because heap-based objects and GC kills RAII. IMHO, being able to put objects on the stack is the greatest single advantage of C++ over Java and makes well-written C++ code MUCH cleaner than well-written Java code.

Answer 2

Yes, I use this technique because of RAII. I also use this technique in plain C since it brings the variables closer together. Of course, I should be thinking about breaking up the functions even more.

One thing I do that is probably stylistically controversial is put the opening curly brace on the line of the declaration or put a comment right on it. I want to decrease the amount of wasted vertical space. This is based on the Google C++ Style Guide recommendation..

/// c++ code
/// references to boost::test
BOOST_TEST_CASE( curly_brace )
{
  // init
  MyClass instance_to_test( "initial", TestCase::STUFF ); {
    instance_to_test.permutate(42u);
    instance_to_test.rotate_left_face();
    instance_to_test.top_gun();
  }
  { // test check
    const uint8_t kEXP_FAP_BOOST = 240u;
    BOOST_CHECK_EQUAL( instance_to_test.get_fap_boost(), kEXP_FAP_BOOST);
  }
}

Answer 3

The most common "non-standard" use of scoping that I use regularly is to utilize a scoped mutex.

void MyClass::Somefun()
{
    //do some stuff
    {
        // example imlementation that has a mutex passed into a lock object:
        scopedMutex lockObject(m_mutex); 

        // protected code here

    } // mutex is unlocked here
    // more code here
}

This has many benefits, but the most important is that the lock will always be cleaned up, even if an exception is thrown in the protected code.

Answer 4

It has its place, but I don't think that doing it so that $foo can be one variable here and a different variable there, within the same function or other (logical, rather than lexical) scope is a good idea. Even though the compiler may understand that perfectly, it seems too likely to make life difficult for humans trying to read the code.

Answer 5

I agree with agartzke. If you feel that you need to segment larger logical code blocks for readability, you should consider refactoring to clean up busy and cluttered members.

Answer 6

I only use it when I need to release something by the means of RAII and even then only when it should be released as early as I possibly can (releasing a lock for example).