Question

Possible Duplicate:
Do-While and if-else statements in C/C++ macros

gcc (GCC) 4.7.2
c89

Hello,

I have the following function-like macro and just wondering what is the preferred usage when using across multiple lines. It it better to use curly braces or do..while(0) loop.

Normally I use a do..while(0) for everything. But I have seen some projects where they just use the curly braces, and I am not sure which one would be better.

do..while

#define DSO_ERROR(msg, res_handle_module, mem_pool, size)   do {        \
        char *dso_error = apr_palloc((apr_pool_t*)mem_pool, size);      \
        apr_dso_error((apr_dso_handle_t*)res_handle_module, (char*)dso_error, (apr_size_t)size); \
        LOG_ERR("%s dso error %s", (char*)msg, dso_error);              \
        goto dso_failure;                                               \
    } while(0); 

curly braces

#define DSO_ERROR(msg, res_handle_module, mem_pool, size) {             \
        char *dso_error = apr_palloc((apr_pool_t*)mem_pool, size);      \
        apr_dso_error((apr_dso_handle_t*)res_handle_module, (char*)dso_error, (apr_size_t)size); \
        LOG_ERR("%s dso error %s", (char*)msg, dso_error);              \
        goto dso_failure;                                               \
    }

The only difference is that a semi-colon will be preset on the do..while loop and not on the curly braces.

Many thanks for any suggestions,

Answer 1

The curly brace version will break usage like this:

if( foo )
  DSO_ERROR("Foo occured!", my_module, the_pool, 4711);
else
  printf("All is well, there is no foo\n");

which is the very reason for the do ... while(0) construct. So that seems worth avoiding.