CODEWITHSUNDEEP
cscopecurly-braces
user12211554
user12211554

Reputation:

Is this practice of manually applying scopes standard C?

Is creating local scopes with just a pair of brackets, would that be considered standard C?

#include <stdio.h>

int main(int argc, char *argv[]) {
    {
        register char x = 'a';
        putchar(x); // works
    }
    //putchar(x); wont work
}

Or is it best to not use this? Is it a GCC compiler extension?

I have once been told that the accepted practice is a do {...} while (0); loop. Is it true that all C compilers will recognise this practice just like it is safe to assume any given C compiler will recognise an if statement?

I tried googling this, and my results were about scope behavior, and had nothing to do with manually applying scopes.

Upvotes: 1

Views: 207

Answers (3)

dbush
dbush

Reputation: 223897

This is standard C.

Section 6.8p1 of the C standard gives the following syntax for a statement:

statement:
  labeled-statement
  compound-statement
  expression-statement
  selection-statement
  iteration-statement
  jump-statement

Where a compound-statement is defined in section 6.8.2p1:

compound-statement:
   { block-item-list(opt) }

block-item-list:
  block-item
  block-item-list block-item

block-item:
  declaration
  statement

What this says is that anyplace that a statement can occur, a compound statement (i.e. a set of statements surrounded by {}) can occur.

Upvotes: 2

Adam Kotwasinski
Adam Kotwasinski

Reputation: 4554

Yes, it is standard; this is creation of block scope, as supported by C language.

Regarding "best to use" part, it depends, certainly it might be a bit confusing to some people.

This might come in very useful with generated code though, so you don't need to bother (as much) with unique identifiers for local vars:

int main(int argc, char *argv[]) {
  {
    int x = 4;
    printf("%d\n", x);
  }
  {
    int x = 5;
    printf("%d\n", x);
  }
}

Upvotes: 5

wildplasser
wildplasser

Reputation: 44250

Yes, it is standard; you can always introduce a new scope with an extra pair of {}

I often use it in conditionally compiled code, to avoid unused variable warnings:

#if DEBUG
    {
    struct node *tmp;
    for (tmp=this; tmp; tmp= tmp->next) {
        printf(stderr, "Node %u: %s\n", tmp->num, tmp->name);
        }
     }
#endif

Upvotes: 2

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