do { … } while (0) — what is it good for? [duplicate]

by

It’s the only construct in C that you can use to #define a multistatement operation, put a semicolon after, and still use within an if statement. An example might help:

#define FOO(x) foo(x); bar(x)

if (condition)
    FOO(x);
else // syntax error here
    ...;

Even using braces doesn’t help:

#define FOO(x) { foo(x); bar(x); }

Using this in an if statement would require that you omit the semicolon, which is counterintuitive:

if (condition)
    FOO(x)
else
    ...

If you define FOO like this:

#define FOO(x) do { foo(x); bar(x); } while (0)

then the following is syntactically correct:

if (condition)
    FOO(x);
else
    ....

More Related Contents:

  1. HOW to back for the beginning if the user press any key except 1 or 2 or 3? [closed]
  2. I need help understanding this code in C [closed]
  3. Simple counters not working in C
  4. break statement doesn’t work in a loop [closed]
  5. How to iterate over this series 5 6 7 6 5 6 7 6 5 6 7 6 5… in C? [closed]
  6. Finding target sum of two numbers in array
  7. How to break out of while loop in C
  8. C loop optimization help for final assignment (with compiler optimization disabled)
  9. Validate the type of input in a do-while loop C
  10. For vs. while in C programming?
  11. Effect of semicolon after ‘for’ loop
  12. Is it faster to count down than it is to count up?
  13. No loop condition in for and while loop
  14. How to optimize these loops (with compiler optimization disabled)?
  15. Validate the type of input in a do-while loop
  16. When implementing an infinite loop, is there a difference in using while(1) vs for(;;) vs goto (in C)?
  17. Is there any way to loop through a struct with elements of different types in C?
  18. How can I optimize these loops (with compiler optimization disabled)?
  19. How can I break out of two nested for loops in Objective-C?
  20. What REALLY happens when you don’t free after malloc before program termination?
  21. size of character array and size of character pointer
  22. Static allocation of opaque data types
  23. Why is strtok causing a segmentation fault?
  24. Is this possible to customize printf?
  25. How do I make an infinite empty loop that won’t be optimized away?
  26. How do I link object files in C? Fails with “Undefined symbols for architecture x86_64”
  27. Is it possible to call a non-exported function that resides in an exe?
  28. PTHREAD_MUTEX_INITIALIZER vs pthread_mutex_init ( &mutex, param)
  29. Why is execstack required to execute code on the heap?
  30. pthread execution on linux

Leave a Comment