Avoid potential undesirable effects caused by macros

The macros provided by this library would expand to an unguarded
conditional that could have potential unwanted consequences. Consider
the following example:

    dynstr_append_or_ret_null(&d, "example");
    else
    {
        /* This is unexpectedly working. */
    }

The example above would expand to:

    if (dynstr_append(__VA_ARGS__) != DYNSTR_OK) return false;
    else
    {
        /* This is unexpectedly working. */
    }

Which is valid C yet allows possibly unexpected behaviour. The solution
is then to enclose these conditions into a `do while (0)` statement.

1 files changed, 8 insertions, 4 deletions

diff --git a/include/dynstr.h b/include/dynstr.h
index a07cf3b..4fc0afa 100644
--- a/include/dynstr.h
+++ b/include/dynstr.h
@@ -30,12 +30,14 @@
 /**
  * Convenience macro that calls dynstr_append and returns NULL if failed.
  */
-#define dynstr_append_or_ret_null(...) if (dynstr_append(__VA_ARGS__) != DYNSTR_OK) return NULL
+#define dynstr_append_or_ret_null(...) \
+   do {if (dynstr_append(__VA_ARGS__) != DYNSTR_OK) return NULL;} while (0)
 
 /**
  * Convenience macro that calls dynstr_append and returns false if failed.
  */
-#define dynstr_append_or_ret_false(...) if (dynstr_append(__VA_ARGS__) != DYNSTR_OK) return false
+#define dynstr_append_or_ret_false(...) \
+   do {if (dynstr_append(__VA_ARGS__) != DYNSTR_OK) return false;} while (0)
 
 /**
  * Convenience macro that calls dynstr_append and returns its error code if failed.
@@ -45,12 +47,14 @@
 /**
  * Convenience macro that calls dynstr_append and returns zero if failed.
  */
-#define dynstr_append_or_ret_zero(...) if (dynstr_append(__VA_ARGS__) != DYNSTR_OK) return 0
+#define dynstr_append_or_ret_zero(...) \
+   do {if (dynstr_append(__VA_ARGS__) != DYNSTR_OK) return 0;} while (0)
 
 /**
  * Convenience macro that calls dynstr_append and returns one if failed.
  */
-#define dynstr_append_or_ret_nonzero(...) if (dynstr_append(__VA_ARGS__) != DYNSTR_OK) return 1
+#define dynstr_append_or_ret_nonzero(...) \
+   do {if (dynstr_append(__VA_ARGS__) != DYNSTR_OK) return 1;} while (0)
 
 /**
  * Dynamic string type used for this library.