[cfe-dev] can foo() be called with arguments?

[Török Edwin]

Hi,

clang is rejecting the code below, but any other compiler I tried
accepts it (some give a warning though).

>From my reading of the C99 standard (N1256.pdf) calling foo with
parameters when it is declared as foo() is allowed only if the
declaration doesn't involve a definition too.
If it involves a definition, then you can't call it with parameters,
and foo() is equivalent to foo(void). Is this correct?

I couldn't find the ANSI C standard online, I don't know what it
says about this.

6.7.5.3.14 Function declarators (including prototypes)
"An identifier list declares only the identifiers of the parameters of
the function. An empty list in a function declarator that is part of
a definition of that function specifies that the function has no
parameters. The empty list in a function declarator that is not part
of a definition of that function specifies that no information about
the number or types of the parameters is supplied.126)"

This is the code in question:
#ifdef DEBUG
#define dbgmsg printf
#else
static void dbgmsg() {}
#endif
int main(void)
{
        dbgmsg("some message:%d",5);
        return 0;
}

Of course the code can be easily changed to
static void dbgmsg(const char *fmt,...){}

Clang rejects it with an error:
$ clang x.c
x.c:8:9: error: too many arguments to function
        dbgmsg("some message:%d",5);
        ~~~~~~ ^~~~~~~~~~~~~~~~~~~
1 diagnostic generated.

GCC accepts it without even giving a warning!
$ gcc -Wall -W x.c
$ gcc --version
gcc (GCC) 4.2.3 (Debian 4.2.3-1)

Other compilers:

$ icc -w2 x.c
x.c(8): warning #140: too many arguments in function call
        dbgmsg("some message:%d",5);
$ icc -V
Intel(R) C Compiler for applications running on Intel(R) 64, Version
10.1    Build 20080112 Package ID: l_cc_p_10.1.012            ^

$ cc x.c
c"x.c", line 8: warning #2140-D: too many arguments in function call
          dbgmsg("some message:%d",5);
$ cc -V
cc: HP C/aC++ B3910B A.06.14 [Feb 22 2007]
                 ^

$ tcc -Wall x.c
$ tcc -v
tcc version 0.9.24

Best regards,
--Edwin