Search code examples
c++syntaxopenmp

what does structured-block refer to?

I now have seen several times that in an explanation of syntax the phrase structured-block was used. For example: 

#pragma omp single
  structured-block

(This is from OpenMP, but that doesn't matter.)

Would the following two lines also count as a structured-block?

do_something1;
do_something2;

or only the first statement alone?

So, to put it shortly: What do they mean when saying structured-block?

Solution

  • Based on the documentation here:

    A “structured block” is a single statement or a compound statement with a single entry at the top and a single exit at the bottom

    Looking up the definition of a compound statement here:

    A compound statement, or block, is a brace-enclosed sequence of statements and declarations.

    Given this definition, do_something1; would be the only one part of the structured block as a new "single" statement begins after that. On the other hand if you did

    #pragma omp <directive>
{
do_something1;
do_something2;
}

    it would have both in the structured block as its a "compound" statement.

    Finally, note the definition stating single entry at the top and a single exit at the bottom. This simply means that we should not have an intermediate exit/control-flow breaking point like a goto statement, return or throw error in between.