diff options
Diffstat (limited to 'gcc/doc')
| -rw-r--r-- | gcc/doc/cpp.texi | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/gcc/doc/cpp.texi b/gcc/doc/cpp.texi index 73785c13794..e8107f2acc4 100644 --- a/gcc/doc/cpp.texi +++ b/gcc/doc/cpp.texi @@ -1620,7 +1620,7 @@ The @code{eprintf} macro above could be written @end example @noindent -using this extension. You cannot use @code{__VA_ARGS__} and this +using this extension. You cannot use @code{@w{__VA_ARGS__}} and this extension in the same macro. You can have named arguments as well as variable arguments in a variadic @@ -1670,6 +1670,15 @@ eprintf ("success!\n") @expansion{} fprintf(stderr, "success!\n"); @end example +@noindent +The above explanation is ambiguous about the case where the only macro +parameter is a variable arguments parameter, as it is meaningless to +try to distinguish whether no argument at all is an empty argument or +a missing argument. In this case the C99 standard is clear that the +comma must remain, however the existing GCC extension used to swallow +the comma. So CPP retains the comma when conforming to a specific C +standard, and drops it otherwise. + C99 mandates that the only place the identifier @code{@w{__VA_ARGS__}} can appear is in the replacement list of a variadic macro. It may not be used as a macro name, macro argument name, or within a different type |
