What is the meaning of do{...} while(0)

    Sometimes we see some codes in C using this pattern: do{...} while(0). It looks it doesn't do anything else but just simply running everything in the braces. When I saw these codes the first time, I also felt weird. Then I did some research and post it. I hope it can help you.

    This pattern is only used in C or C++’s conditional compilation and when you want to use #define to represent multiple statements. A simple sample is like this:

#define function(x)  do { a(x); b(x); }while (0)

so, we can use it like this:

if(some condition){

    function(x);

}

else 

      blah blah....

     Why we have to use this pattern? When you want to use #define to represent multiple statements, 

this statement wouldn't work:

#define function(x)  foo(x); bar(x)   //cause syntax error in the if statement




this statement still won't work:

#define FOO(x) { foo(x); bar(x); } // doesn't work

only in this pattern:

#define function(x)  do { a(x); b(x); }while (0)

It work well in the if statement.

That is my study about this thing. I hope I can help you.

Hua