CODEWITHSUNDEEP
c++syntaxopenmp
MMM
MMM

Reputation: 383

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?

Upvotes: 0

Views: 502

Answers (2)

tangy
tangy

Reputation: 3256

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.

Upvotes: 1

Michael Klemm
Michael Klemm

Reputation: 2853

structured-block is either a single statement, like

printf("Hello\n");

or a sequence of statements enclosed in curly braces:

{
    printf("Hello ");
    printf("World\n");
}

In addition, OpenMP requires "single entry, single exit", so that means that you cannot have a goto or similar branching into the block and that you cannot have a branch leaving the block, e.g. goto or in C++ an exception. Instead, the code needs to reach the closing curly brace.

Upvotes: 1

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